// SPDX-License-Identifier: GPL-2.0
/* kernel/rwsem.c: R/W semaphores, public implementation
*
* Written by David Howells ([email protected]).
* Derived from asm-i386/semaphore.h
*
* Writer lock-stealing by Alex Shi <[email protected]>
* and Michel Lespinasse <[email protected]>
*
* Optimistic spinning by Tim Chen <[email protected]>
* and Davidlohr Bueso <[email protected]>. Based on mutexes.
*
* Rwsem count bit fields re-definition and rwsem rearchitecture by
* Waiman Long <[email protected]> and
* Peter Zijlstra <[email protected]>.
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/sched/task.h>
#include <linux/sched/debug.h>
#include <linux/sched/wake_q.h>
#include <linux/sched/signal.h>
#include <linux/sched/clock.h>
#include <linux/export.h>
#include <linux/rwsem.h>
#include <linux/atomic.h>
#include <trace/events/lock.h>
#ifndef CONFIG_PREEMPT_RT
#include "lock_events.h"
/*
* The least significant 2 bits of the owner value has the following
* meanings when set.
* - Bit 0: RWSEM_READER_OWNED - rwsem may be owned by readers (just a hint)
* - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
*
* When the rwsem is reader-owned and a spinning writer has timed out,
* the nonspinnable bit will be set to disable optimistic spinning.
* When a writer acquires a rwsem, it puts its task_struct pointer
* into the owner field. It is cleared after an unlock.
*
* When a reader acquires a rwsem, it will also puts its task_struct
* pointer into the owner field with the RWSEM_READER_OWNED bit set.
* On unlock, the owner field will largely be left untouched. So
* for a free or reader-owned rwsem, the owner value may contain
* information about the last reader that acquires the rwsem.
*
* That information may be helpful in debugging cases where the system
* seems to hang on a reader owned rwsem especially if only one reader
* is involved. Ideally we would like to track all the readers that own
* a rwsem, but the overhead is simply too big.
*
* A fast path reader optimistic lock stealing is supported when the rwsem
* is previously owned by a writer and the following conditions are met:
* - rwsem is not currently writer owned
* - the handoff isn't set.
*/
#define RWSEM_READER_OWNED (1UL << 0)
#define RWSEM_NONSPINNABLE (1UL << 1)
#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
#ifdef CONFIG_DEBUG_RWSEMS
# define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
if (!debug_locks_silent && \
WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
#c, atomic_long_read(&(sem)->count), \
(unsigned long) sem->magic, \
atomic_long_read(&(sem)->owner), (long)current, \
list_empty(&(sem)->wait_list) ? "" : "not ")) \
debug_locks_off(); \
} while (0)
#else
# define DEBUG_RWSEMS_WARN_ON(c, sem)
#endif
/*
* On 64-bit architectures, the bit definitions of the count are:
*
* Bit 0 - writer locked bit
* Bit 1 - waiters present bit
* Bit 2 - lock handoff bit
* Bits 3-7 - reserved
* Bits 8-62 - 55-bit reader count
* Bit 63 - read fail bit
*
* On 32-bit architectures, the bit definitions of the count are:
*
* Bit 0 - writer locked bit
* Bit 1 - waiters present bit
* Bit 2 - lock handoff bit
* Bits 3-7 - reserved
* Bits 8-30 - 23-bit reader count
* Bit 31 - read fail bit
*
* It is not likely that the most significant bit (read fail bit) will ever
* be set. This guard bit is still checked anyway in the down_read() fastpath
* just in case we need to use up more of the reader bits for other purpose
* in the future.
*
* atomic_long_fetch_add() is used to obtain reader lock, whereas
* atomic_long_cmpxchg() will be used to obtain writer lock.
*
* There are three places where the lock handoff bit may be set or cleared.
* 1) rwsem_mark_wake() for readers -- set, clear
* 2) rwsem_try_write_lock() for writers -- set, clear
* 3) rwsem_del_waiter() -- clear
*
* For all the above cases, wait_lock will be held. A writer must also
* be the first one in the wait_list to be eligible for setting the handoff
* bit. So concurrent setting/clearing of handoff bit is not possible.
*/
#define RWSEM_WRITER_LOCKED (1UL << 0)
#define RWSEM_FLAG_WAITERS (1UL << 1)
#define RWSEM_FLAG_HANDOFF (1UL << 2)
#define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
#define RWSEM_READER_SHIFT 8
#define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)
#define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))
#define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED
#define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
#define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
/*
* All writes to owner are protected by WRITE_ONCE() to make sure that
* store tearing can't happen as optimistic spinners may read and use
* the owner value concurrently without lock. Read from owner, however,
* may not need READ_ONCE() as long as the pointer value is only used
* for comparison and isn't being dereferenced.
*
* Both rwsem_{set,clear}_owner() functions should be in the same
* preempt disable section as the atomic op that changes sem->count.
*/
static inline void rwsem_set_owner(struct rw_semaphore *sem)
{
lockdep_assert_preemption_disabled();
atomic_long_set(&sem->owner, (long)current);
}
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
{
lockdep_assert_preemption_disabled();
atomic_long_set(&sem->owner, 0);
}
/*
* Test the flags in the owner field.
*/
static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
{
return atomic_long_read(&sem->owner) & flags;
}
/*
* The task_struct pointer of the last owning reader will be left in
* the owner field.
*
* Note that the owner value just indicates the task has owned the rwsem
* previously, it may not be the real owner or one of the real owners
* anymore when that field is examined, so take it with a grain of salt.
*
* The reader non-spinnable bit is preserved.
*/
static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
struct task_struct *owner)
{
unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
(atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
atomic_long_set(&sem->owner, val);
}
static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
{
__rwsem_set_reader_owned(sem, current);
}
#ifdef CONFIG_DEBUG_RWSEMS
/*
* Return just the real task structure pointer of the owner
*/
static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
{
return (struct task_struct *)
(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
}
/*
* Return true if the rwsem is owned by a reader.
*/
static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
{
/*
* Check the count to see if it is write-locked.
*/
long count = atomic_long_read(&sem->count);
if (count & RWSEM_WRITER_MASK)
return false;
return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
}
/*
* With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
* is a task pointer in owner of a reader-owned rwsem, it will be the
* real owner or one of the real owners. The only exception is when the
* unlock is done by up_read_non_owner().
*/
static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
{
unsigned long val = atomic_long_read(&sem->owner);
while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
if (atomic_long_try_cmpxchg(&sem->owner, &val,
val & RWSEM_OWNER_FLAGS_MASK))
return;
}
}
#else
static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
{
}
#endif
/*
* Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
* remains set. Otherwise, the operation will be aborted.
*/
static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
{
unsigned long owner = atomic_long_read(&sem->owner);
do {
if (!(owner & RWSEM_READER_OWNED))
break;
if (owner & RWSEM_NONSPINNABLE)
break;
} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
owner | RWSEM_NONSPINNABLE));
}
static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
{
*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
if (WARN_ON_ONCE(*cntp < 0))
rwsem_set_nonspinnable(sem);
if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
rwsem_set_reader_owned(sem);
return true;
}
return false;
}
static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
{
long tmp = RWSEM_UNLOCKED_VALUE;
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
return true;
}
return false;
}
/*
* Return the real task structure pointer of the owner and the embedded
* flags in the owner. pflags must be non-NULL.
*/
static inline struct task_struct *
rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
{
unsigned long owner = atomic_long_read(&sem->owner);
*pflags = owner & RWSEM_OWNER_FLAGS_MASK;
return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
}
/*
* Guide to the rw_semaphore's count field.
*
* When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
* by a writer.
*
* The lock is owned by readers when
* (1) the RWSEM_WRITER_LOCKED isn't set in count,
* (2) some of the reader bits are set in count, and
* (3) the owner field has RWSEM_READ_OWNED bit set.
*
* Having some reader bits set is not enough to guarantee a readers owned
* lock as the readers may be in the process of backing out from the count
* and a writer has just released the lock. So another writer may steal
* the lock immediately after that.
*/
/*
* Initialize an rwsem:
*/
void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/*
* Make sure we are not reinitializing a held semaphore:
*/
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
#endif
#ifdef CONFIG_DEBUG_RWSEMS
sem->magic = sem;
#endif
atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
raw_spin_lock_init(&sem->wait_lock);
INIT_LIST_HEAD(&sem->wait_list);
atomic_long_set(&sem->owner, 0L);
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
osq_lock_init(&sem->osq);
#endif
}
EXPORT_SYMBOL(__init_rwsem);
enum rwsem_waiter_type {
RWSEM_WAITING_FOR_WRITE,
RWSEM_WAITING_FOR_READ
};
struct rwsem_waiter {
struct list_head list;
struct task_struct *task;
enum rwsem_waiter_type type;
unsigned long timeout;
bool handoff_set;
};
#define rwsem_first_waiter(sem) \
list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
enum rwsem_wake_type {
RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */
RWSEM_WAKE_READERS, /* Wake readers only */
RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */
};
/*
* The typical HZ value is either 250 or 1000. So set the minimum waiting
* time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
* queue before initiating the handoff protocol.
*/
#define RWSEM_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
/*
* Magic number to batch-wakeup waiting readers, even when writers are
* also present in the queue. This both limits the amount of work the
* waking thread must do and also prevents any potential counter overflow,
* however unlikely.
*/
#define MAX_READERS_WAKEUP 0x100
static inline void
rwsem_add_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
{
lockdep_assert_held(&sem->wait_lock);
list_add_tail(&waiter->list, &sem->wait_list);
/* caller will set RWSEM_FLAG_WAITERS */
}
/*
* Remove a waiter from the wait_list and clear flags.
*
* Both rwsem_mark_wake() and rwsem_try_write_lock() contain a full 'copy' of
* this function. Modify with care.
*
* Return: true if wait_list isn't empty and false otherwise
*/
static inline bool
rwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
{
lockdep_assert_held(&sem->wait_lock);
list_del(&waiter->list);
if (likely(!list_empty(&sem->wait_list)))
return true;
atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count);
return false;
}
/*
* handle the lock release when processes blocked on it that can now run
* - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
* have been set.
* - there must be someone on the queue
* - the wait_lock must be held by the caller
* - tasks are marked for wakeup, the caller must later invoke wake_up_q()
* to actually wakeup the blocked task(s) and drop the reference count,
* preferably when the wait_lock is released
* - woken process blocks are discarded from the list after having task zeroed
* - writers are only marked woken if downgrading is false
*
* Implies rwsem_del_waiter() for all woken readers.
*/
static void rwsem_mark_wake(struct rw_semaphore *sem,
enum rwsem_wake_type wake_type,
struct wake_q_head *wake_q)
{
struct rwsem_waiter *waiter, *tmp;
long oldcount, woken = 0, adjustment = 0;
struct list_head wlist;
lockdep_assert_held(&sem->wait_lock);
/*
* Take a peek at the queue head waiter such that we can determine
* the wakeup(s) to perform.
*/
waiter = rwsem_first_waiter(sem);
if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
if (wake_type == RWSEM_WAKE_ANY) {
/*
* Mark writer at the front of the queue for wakeup.
* Until the task is actually later awoken later by
* the caller, other writers are able to steal it.
* Readers, on the other hand, will block as they
* will notice the queued writer.
*/
wake_q_add(wake_q, waiter->task);
lockevent_inc(rwsem_wake_writer);
}
return;
}
/*
* No reader wakeup if there are too many of them already.
*/
if (unlikely(atomic_long_read(&sem->count) < 0))
return;
/*
* Writers might steal the lock before we grant it to the next reader.
* We prefer to do the first reader grant before counting readers
* so we can bail out early if a writer stole the lock.
*/
if (wake_type != RWSEM_WAKE_READ_OWNED) {
struct task_struct *owner;
adjustment = RWSEM_READER_BIAS;
oldcount = atomic_long_fetch_add(adjustment, &sem->count);
if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
/*
* When we've been waiting "too" long (for writers
* to give up the lock), request a HANDOFF to
* force the issue.
*/
if (time_after(jiffies, waiter->timeout)) {
if (!(oldcount & RWSEM_FLAG_HANDOFF)) {
adjustment -= RWSEM_FLAG_HANDOFF;
lockevent_inc(rwsem_rlock_handoff);
}
waiter->handoff_set = true;
}
atomic_long_add(-adjustment, &sem->count);
return;
}
/*
* Set it to reader-owned to give spinners an early
* indication that readers now have the lock.
* The reader nonspinnable bit seen at slowpath entry of
* the reader is copied over.
*/
owner = waiter->task;
__rwsem_set_reader_owned(sem, owner);
}
/*
* Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
* queue. We know that the woken will be at least 1 as we accounted
* for above. Note we increment the 'active part' of the count by the
* number of readers before waking any processes up.
*
* This is an adaptation of the phase-fair R/W locks where at the
* reader phase (first waiter is a reader), all readers are eligible
* to acquire the lock at the same time irrespective of their order
* in the queue. The writers acquire the lock according to their
* order in the queue.
*
* We have to do wakeup in 2 passes to prevent the possibility that
* the reader count may be decremented before it is incremented. It
* is because the to-be-woken waiter may not have slept yet. So it
* may see waiter->task got cleared, finish its critical section and
* do an unlock before the reader count increment.
*
* 1) Collect the read-waiters in a separate list, count them and
* fully increment the reader count in rwsem.
* 2) For each waiters in the new list, clear waiter->task and
* put them into wake_q to be woken up later.
*/
INIT_LIST_HEAD(&wlist);
list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
if (waiter->type == RWSEM_WAITING_FOR_WRITE)
continue;
woken++;
list_move_tail(&waiter->list, &wlist);
/*
* Limit # of readers that can be woken up per wakeup call.
*/
if (unlikely(woken >= MAX_READERS_WAKEUP))
break;
}
adjustment = woken * RWSEM_READER_BIAS - adjustment;
lockevent_cond_inc(rwsem_wake_reader, woken);
oldcount = atomic_long_read(&sem->count);
if (list_empty(&sem->wait_list)) {
/*
* Combined with list_move_tail() above, this implies
* rwsem_del_waiter().
*/
adjustment -= RWSEM_FLAG_WAITERS;
if (oldcount & RWSEM_FLAG_HANDOFF)
adjustment -= RWSEM_FLAG_HANDOFF;
} else if (woken) {
/*
* When we've woken a reader, we no longer need to force
* writers to give up the lock and we can clear HANDOFF.
*/
if (oldcount & RWSEM_FLAG_HANDOFF)
adjustment -= RWSEM_FLAG_HANDOFF;
}
if (adjustment)
atomic_long_add(adjustment, &sem->count);
/* 2nd pass */
list_for_each_entry_safe(waiter, tmp, &wlist, list) {
struct task_struct *tsk;
tsk = waiter->task;
get_task_struct(tsk);
/*
* Ensure calling get_task_struct() before setting the reader
* waiter to nil such that rwsem_down_read_slowpath() cannot
* race with do_exit() by always holding a reference count
* to the task to wakeup.
*/
smp_store_release(&waiter->task, NULL);
/*
* Ensure issuing the wakeup (either by us or someone else)
* after setting the reader waiter to nil.
*/
wake_q_add_safe(wake_q, tsk);
}
}
/*
* Remove a waiter and try to wake up other waiters in the wait queue
* This function is called from the out_nolock path of both the reader and
* writer slowpaths with wait_lock held. It releases the wait_lock and
* optionally wake up waiters before it returns.
*/
static inline void
rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter,
struct wake_q_head *wake_q)
__releases(&sem->wait_lock)
{
bool first = rwsem_first_waiter(sem) == waiter;
wake_q_init(wake_q);
/*
* If the wait_list isn't empty and the waiter to be deleted is
* the first waiter, we wake up the remaining waiters as they may
* be eligible to acquire or spin on the lock.
*/
if (rwsem_del_waiter(sem, waiter) && first)
rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
if (!wake_q_empty(wake_q))
wake_up_q(wake_q);
}
/*
* This function must be called with the sem->wait_lock held to prevent
* race conditions between checking the rwsem wait list and setting the
* sem->count accordingly.
*
* Implies rwsem_del_waiter() on success.
*/
static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
struct rwsem_waiter *waiter)
{
struct rwsem_waiter *first = rwsem_first_waiter(sem);
long count, new;
lockdep_assert_held(&sem->wait_lock);
count = atomic_long_read(&sem->count);
do {
bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
if (has_handoff) {
/*
* Honor handoff bit and yield only when the first
* waiter is the one that set it. Otherwisee, we
* still try to acquire the rwsem.
*/
if (first->handoff_set && (waiter != first))
return false;
}
new = count;
if (count & RWSEM_LOCK_MASK) {
/*
* A waiter (first or not) can set the handoff bit
* if it is an RT task or wait in the wait queue
* for too long.
*/
if (has_handoff || (!rt_or_dl_task(waiter->task) &&
!time_after(jiffies, waiter->timeout)))
return false;
new |= RWSEM_FLAG_HANDOFF;
} else {
new |= RWSEM_WRITER_LOCKED;
new &= ~RWSEM_FLAG_HANDOFF;
if (list_is_singular(&sem->wait_list))
new &= ~RWSEM_FLAG_WAITERS;
}
} while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
/*
* We have either acquired the lock with handoff bit cleared or set
* the handoff bit. Only the first waiter can have its handoff_set
* set here to enable optimistic spinning in slowpath loop.
*/
if (new & RWSEM_FLAG_HANDOFF) {
first->handoff_set = true;
lockevent_inc(rwsem_wlock_handoff);
return false;
}
/*
* Have rwsem_try_write_lock() fully imply rwsem_del_waiter() on
* success.
*/
list_del(&waiter->list);
rwsem_set_owner(sem);
return true;
}
/*
* The rwsem_spin_on_owner() function returns the following 4 values
* depending on the lock owner state.
* OWNER_NULL : owner is currently NULL
* OWNER_WRITER: when owner changes and is a writer
* OWNER_READER: when owner changes and the new owner may be a reader.
* OWNER_NONSPINNABLE:
* when optimistic spinning has to stop because either the
* owner stops running, is unknown, or its timeslice has
* been used up.
*/
enum owner_state {
OWNER_NULL = 1 << 0,
OWNER_WRITER = 1 << 1,
OWNER_READER = 1 << 2,
OWNER_NONSPINNABLE = 1 << 3,
};
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
/*
* Try to acquire write lock before the writer has been put on wait queue.
*/
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
{
long count = atomic_long_read(&sem->count);
while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
count | RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
lockevent_inc(rwsem_opt_lock);
return true;
}
}
return false;
}
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *owner;
unsigned long flags;
bool ret = true;
if (need_resched()) {
lockevent_inc(rwsem_opt_fail);
return false;
}
/*
* Disable preemption is equal to the RCU read-side crital section,
* thus the task_strcut structure won't go away.
*/
owner = rwsem_owner_flags(sem, &flags);
/*
* Don't check the read-owner as the entry may be stale.
*/
if ((flags & RWSEM_NONSPINNABLE) ||
(owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
ret = false;
lockevent_cond_inc(rwsem_opt_fail, !ret);
return ret;
}
#define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
static inline enum owner_state
rwsem_owner_state(struct task_struct *owner, unsigned long flags)
{
if (flags & RWSEM_NONSPINNABLE)
return OWNER_NONSPINNABLE;
if (flags & RWSEM_READER_OWNED)
return OWNER_READER;
return owner ? OWNER_WRITER : OWNER_NULL;
}
static noinline enum owner_state
rwsem_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *new, *owner;
unsigned long flags, new_flags;
enum owner_state state;
lockdep_assert_preemption_disabled();
owner = rwsem_owner_flags(sem, &flags);
state = rwsem_owner_state(owner, flags);
if (state != OWNER_WRITER)
return state;
for (;;) {
/*
* When a waiting writer set the handoff flag, it may spin
* on the owner as well. Once that writer acquires the lock,
* we can spin on it. So we don't need to quit even when the
* handoff bit is set.
*/
new = rwsem_owner_flags(sem, &new_flags);
if ((new != owner) || (new_flags != flags)) {
state = rwsem_owner_state(new, new_flags);
break;
}
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking sem->owner still matches owner, if that fails,
* owner might point to free()d memory, if it still matches,
* our spinning context already disabled preemption which is
* equal to RCU read-side crital section ensures the memory
* stays valid.
*/
barrier();
if (need_resched() || !owner_on_cpu(owner)) {
state = OWNER_NONSPINNABLE;
break;
}
cpu_relax();
}
return state;
}
/*
* Calculate reader-owned rwsem spinning threshold for writer
*
* The more readers own the rwsem, the longer it will take for them to
* wind down and free the rwsem. So the empirical formula used to
* determine the actual spinning time limit here is:
*
* Spinning threshold = (10 + nr_readers/2)us
*
* The limit is capped to a maximum of 25us (30 readers). This is just
* a heuristic and is subjected to change in the future.
*/
static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
{
long count = atomic_long_read(&sem->count);
int readers = count >> RWSEM_READER_SHIFT;
u64 delta;
if (readers > 30)
readers = 30;
delta = (20 + readers) * NSEC_PER_USEC / 2;
return sched_clock() + delta;
}
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
bool taken = false;
int prev_owner_state = OWNER_NULL;
int loop = 0;
u64 rspin_threshold = 0;
/* sem->wait_lock should not be held when doing optimistic spinning */
if (!osq_lock(&sem->osq))
goto done;
/*
* Optimistically spin on the owner field and attempt to acquire the
* lock whenever the owner changes. Spinning will be stopped when:
* 1) the owning writer isn't running; or
* 2) readers own the lock and spinning time has exceeded limit.
*/
for (;;) {
enum owner_state owner_state;
owner_state = rwsem_spin_on_owner(sem);
if (!(owner_state & OWNER_SPINNABLE))
break;
/*
* Try to acquire the lock
*/
taken = rwsem_try_write_lock_unqueued(sem);
if (taken)
break;
/*
* Time-based reader-owned rwsem optimistic spinning
*/
if (owner_state == OWNER_READER) {
/*
* Re-initialize rspin_threshold every time when
* the owner state changes from non-reader to reader.
* This allows a writer to steal the lock in between
* 2 reader phases and have the threshold reset at
* the beginning of the 2nd reader phase.
*/
if (prev_owner_state != OWNER_READER) {
if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
break;
rspin_threshold = rwsem_rspin_threshold(sem);
loop = 0;
}
/*
* Check time threshold once every 16 iterations to
* avoid calling sched_clock() too frequently so
* as to reduce the average latency between the times
* when the lock becomes free and when the spinner
* is ready to do a trylock.
*/
else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
rwsem_set_nonspinnable(sem);
lockevent_inc(rwsem_opt_nospin);
break;
}
}
/*
* An RT task cannot do optimistic spinning if it cannot
* be sure the lock holder is running or live-lock may
* happen if the current task and the lock holder happen
* to run in the same CPU. However, aborting optimistic
* spinning while a NULL owner is detected may miss some
* opportunity where spinning can continue without causing
* problem.
*
* There are 2 possible cases where an RT task may be able
* to continue spinning.
*
* 1) The lock owner is in the process of releasing the
* lock, sem->owner is cleared but the lock has not
* been released yet.
* 2) The lock was free and owner cleared, but another
* task just comes in and acquire the lock before
* we try to get it. The new owner may be a spinnable
* writer.
*
* To take advantage of two scenarios listed above, the RT
* task is made to retry one more time to see if it can
* acquire the lock or continue spinning on the new owning
* writer. Of course, if the time lag is long enough or the
* new owner is not a writer or spinnable, the RT task will
* quit spinning.
*
* If the owner is a writer, the need_resched() check is
* done inside rwsem_spin_on_owner(). If the owner is not
* a writer, need_resched() check needs to be done here.
*/
if (owner_state != OWNER_WRITER) {
if (need_resched())
break;
if (rt_or_dl_task(current) &&
(prev_owner_state != OWNER_WRITER))
break;
}
prev_owner_state = owner_state;
/*
* The cpu_relax() call is a compiler barrier which forces
* everything in this loop to be re-loaded. We don't need
* memory barriers as we'll eventually observe the right
* values at the cost of a few extra spins.
*/
cpu_relax();
}
osq_unlock(&sem->osq);
done:
lockevent_cond_inc(rwsem_opt_fail, !taken);
return taken;
}
/*
* Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should
* only be called when the reader count reaches 0.
*/
static inline void clear_nonspinnable(struct rw_semaphore *sem)
{
if (unlikely(rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)))
atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);
}
#else
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
return false;
}
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
return false;
}
static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
static inline enum owner_state
rwsem_spin_on_owner(struct rw_semaphore *sem)
{
return OWNER_NONSPINNABLE;
}
#endif
/*
* Prepare to wake up waiter(s) in the wait queue by putting them into the
* given wake_q if the rwsem lock owner isn't a writer. If rwsem is likely
* reader-owned, wake up read lock waiters in queue front or wake up any
* front waiter otherwise.
* This is being called from both reader and writer slow paths.
*/
static inline void rwsem_cond_wake_waiter(struct rw_semaphore *sem, long count,
struct wake_q_head *wake_q)
{
enum rwsem_wake_type wake_type;
if (count & RWSEM_WRITER_MASK)
return;
if (count & RWSEM_READER_MASK) {
wake_type = RWSEM_WAKE_READERS;
} else {
wake_type = RWSEM_WAKE_ANY;
clear_nonspinnable(sem);
}
rwsem_mark_wake(sem, wake_type, wake_q);
}
/*
* Wait for the read lock to be granted
*/
static struct rw_semaphore __sched *
rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int state)
{
long adjustment = -RWSEM_READER_BIAS;
long rcnt = (count >> RWSEM_READER_SHIFT);
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
/*
* To prevent a constant stream of readers from starving a sleeping
* writer, don't attempt optimistic lock stealing if the lock is
* very likely owned by readers.
*/
if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
(rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
goto queue;
/*
* Reader optimistic lock stealing.
*/
if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
rwsem_set_reader_owned(sem);
lockevent_inc(rwsem_rlock_steal);
/*
* Wake up other readers in the wait queue if it is
* the first reader.
*/
if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {
raw_spin_lock_irq(&sem->wait_lock);
if (!list_empty(&sem->wait_list))
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
&wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
wake_up_q(&wake_q);
}
return sem;
}
queue:
waiter.task = current;
waiter.type = RWSEM_WAITING_FOR_READ;
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
waiter.handoff_set = false;
raw_spin_lock_irq(&sem->wait_lock);
if (list_empty(&sem->wait_list)) {
/*
* In case the wait queue is empty and the lock isn't owned
* by a writer, this reader can exit the slowpath and return
* immediately as its RWSEM_READER_BIAS has already been set
* in the count.
*/
if (!(atomic_long_read(&sem->count) & RWSEM_WRITER_MASK)) {
/* Provide lock ACQUIRE */
smp_acquire__after_ctrl_dep();
raw_spin_unlock_irq(&sem->wait_lock);
rwsem_set_reader_owned(sem);
lockevent_inc(rwsem_rlock_fast);
return sem;
}
adjustment += RWSEM_FLAG_WAITERS;
}
rwsem_add_waiter(sem, &waiter);
/* we're now waiting on the lock, but no longer actively locking */
count = atomic_long_add_return(adjustment, &sem->count);
rwsem_cond_wake_waiter(sem, count, &wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
if (!wake_q_empty(&wake_q))
wake_up_q(&wake_q);
trace_contention_begin(sem, LCB_F_READ);
/* wait to be given the lock */
for (;;) {
set_current_state(state);
if (!smp_load_acquire(&waiter.task)) {
/* Matches rwsem_mark_wake()'s smp_store_release(). */
break;
}
if (signal_pending_state(state, current)) {
raw_spin_lock_irq(&sem->wait_lock);
if (waiter.task)
goto out_nolock;
raw_spin_unlock_irq(&sem->wait_lock);
/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
break;
}
schedule_preempt_disabled();
lockevent_inc(rwsem_sleep_reader);
}
__set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock);
trace_contention_end(sem, 0);
return sem;
out_nolock:
rwsem_del_wake_waiter(sem, &waiter, &wake_q);
__set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock_fail);
trace_contention_end(sem, -EINTR);
return ERR_PTR(-EINTR);
}
/*
* Wait until we successfully acquire the write lock
*/
static struct rw_semaphore __sched *
rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
{
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
/* do optimistic spinning and steal lock if possible */
if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {
/* rwsem_optimistic_spin() implies ACQUIRE on success */
return sem;
}
/*
* Optimistic spinning failed, proceed to the slowpath
* and block until we can acquire the sem.
*/
waiter.task = current;
waiter.type = RWSEM_WAITING_FOR_WRITE;
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
waiter.handoff_set = false;
raw_spin_lock_irq(&sem->wait_lock);
rwsem_add_waiter(sem, &waiter);
/* we're now waiting on the lock */
if (rwsem_first_waiter(sem) != &waiter) {
rwsem_cond_wake_waiter(sem, atomic_long_read(&sem->count),
&wake_q);
if (!wake_q_empty(&wake_q)) {
/*
* We want to minimize wait_lock hold time especially
* when a large number of readers are to be woken up.
*/
raw_spin_unlock_irq(&sem->wait_lock);
wake_up_q(&wake_q);
raw_spin_lock_irq(&sem->wait_lock);
}
} else {
atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
}
/* wait until we successfully acquire the lock */
set_current_state(state);
trace_contention_begin(sem, LCB_F_WRITE);
for (;;) {
if (rwsem_try_write_lock(sem, &waiter)) {
/* rwsem_try_write_lock() implies ACQUIRE on success */
break;
}
raw_spin_unlock_irq(&sem->wait_lock);
if (signal_pending_state(state, current))
goto out_nolock;
/*
* After setting the handoff bit and failing to acquire
* the lock, attempt to spin on owner to accelerate lock
* transfer. If the previous owner is a on-cpu writer and it
* has just released the lock, OWNER_NULL will be returned.
* In this case, we attempt to acquire the lock again
* without sleeping.
*/
if (waiter.handoff_set) {
enum owner_state owner_state;
owner_state = rwsem_spin_on_owner(sem);
if (owner_state == OWNER_NULL)
goto trylock_again;
}
schedule_preempt_disabled();
lockevent_inc(rwsem_sleep_writer);
set_current_state(state);
trylock_again:
raw_spin_lock_irq(&sem->wait_lock);
}
__set_current_state(TASK_RUNNING);
raw_spin_unlock_irq(&sem->wait_lock);
lockevent_inc(rwsem_wlock);
trace_contention_end(sem, 0);
return sem;
out_nolock:
__set_current_state(TASK_RUNNING);
raw_spin_lock_irq(&sem->wait_lock);
rwsem_del_wake_waiter(sem, &waiter, &wake_q);
lockevent_inc(rwsem_wlock_fail);
trace_contention_end(sem, -EINTR);
return ERR_PTR(-EINTR);
}
/*
* handle waking up a waiter on the semaphore
* - up_read/up_write has decremented the active part of count if we come here
*/
static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
{
unsigned long flags;
DEFINE_WAKE_Q(wake_q);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (!list_empty(&sem->wait_list))
rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
wake_up_q(&wake_q);
return sem;
}
/*
* downgrade a write lock into a read lock
* - caller incremented waiting part of count and discovered it still negative
* - just wake up any readers at the front of the queue
*/
static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
{
unsigned long flags;
DEFINE_WAKE_Q(wake_q);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (!list_empty(&sem->wait_list))
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
wake_up_q(&wake_q);
return sem;
}
/*
* lock for reading
*/
static __always_inline int __down_read_common(struct rw_semaphore *sem, int state)
{
int ret = 0;
long count;
preempt_disable();
if (!rwsem_read_trylock(sem, &count)) {
if (IS_ERR(rwsem_down_read_slowpath(sem, count, state))) {
ret = -EINTR;
goto out;
}
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
}
out:
preempt_enable();
return ret;
}
static __always_inline void __down_read(struct rw_semaphore *sem)
{
__down_read_common(sem, TASK_UNINTERRUPTIBLE);
}
static __always_inline int __down_read_interruptible(struct rw_semaphore *sem)
{
return __down_read_common(sem, TASK_INTERRUPTIBLE);
}
static __always_inline int __down_read_killable(struct rw_semaphore *sem)
{
return __down_read_common(sem, TASK_KILLABLE);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
int ret = 0;
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
preempt_disable();
tmp = atomic_long_read(&sem->count);
while (!(tmp & RWSEM_READ_FAILED_MASK)) {
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
tmp + RWSEM_READER_BIAS)) {
rwsem_set_reader_owned(sem);
ret = 1;
break;
}
}
preempt_enable();
return ret;
}
/*
* lock for writing
*/
static __always_inline int __down_write_common(struct rw_semaphore *sem, int state)
{
int ret = 0;
preempt_disable();
if (unlikely(!rwsem_write_trylock(sem))) {
if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
ret = -EINTR;
}
preempt_enable();
return ret;
}
static __always_inline void __down_write(struct rw_semaphore *sem)
{
__down_write_common(sem, TASK_UNINTERRUPTIBLE);
}
static __always_inline int __down_write_killable(struct rw_semaphore *sem)
{
return __down_write_common(sem, TASK_KILLABLE);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
int ret;
preempt_disable();
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
ret = rwsem_write_trylock(sem);
preempt_enable();
return ret;
}
/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
{
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
preempt_disable();
rwsem_clear_reader_owned(sem);
tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
RWSEM_FLAG_WAITERS)) {
clear_nonspinnable(sem);
rwsem_wake(sem);
}
preempt_enable();
}
/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
/*
* sem->owner may differ from current if the ownership is transferred
* to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
*/
DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
!rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
preempt_disable();
rwsem_clear_owner(sem);
tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
if (unlikely(tmp & RWSEM_FLAG_WAITERS))
rwsem_wake(sem);
preempt_enable();
}
/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
long tmp;
/*
* When downgrading from exclusive to shared ownership,
* anything inside the write-locked region cannot leak
* into the read side. In contrast, anything in the
* read-locked region is ok to be re-ordered into the
* write side. As such, rely on RELEASE semantics.
*/
DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
preempt_disable();
tmp = atomic_long_fetch_add_release(
-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
rwsem_set_reader_owned(sem);
if (tmp & RWSEM_FLAG_WAITERS)
rwsem_downgrade_wake(sem);
preempt_enable();
}
#else /* !CONFIG_PREEMPT_RT */
#define RT_MUTEX_BUILD_MUTEX
#include "rtmutex.c"
#define rwbase_set_and_save_current_state(state) \
set_current_state(state)
#define rwbase_restore_current_state() \
__set_current_state(TASK_RUNNING)
#define rwbase_rtmutex_lock_state(rtm, state) \
__rt_mutex_lock(rtm, state)
#define rwbase_rtmutex_slowlock_locked(rtm, state) \
__rt_mutex_slowlock_locked(rtm, NULL, state)
#define rwbase_rtmutex_unlock(rtm) \
__rt_mutex_unlock(rtm)
#define rwbase_rtmutex_trylock(rtm) \
__rt_mutex_trylock(rtm)
#define rwbase_signal_pending_state(state, current) \
signal_pending_state(state, current)
#define rwbase_pre_schedule() \
rt_mutex_pre_schedule()
#define rwbase_schedule() \
rt_mutex_schedule()
#define rwbase_post_schedule() \
rt_mutex_post_schedule()
#include "rwbase_rt.c"
void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key)
{
init_rwbase_rt(&(sem)->rwbase);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
#endif
}
EXPORT_SYMBOL(__init_rwsem);
static inline void __down_read(struct rw_semaphore *sem)
{
rwbase_read_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
}
static inline int __down_read_interruptible(struct rw_semaphore *sem)
{
return rwbase_read_lock(&sem->rwbase, TASK_INTERRUPTIBLE);
}
static inline int __down_read_killable(struct rw_semaphore *sem)
{
return rwbase_read_lock(&sem->rwbase, TASK_KILLABLE);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
return rwbase_read_trylock(&sem->rwbase);
}
static inline void __up_read(struct rw_semaphore *sem)
{
rwbase_read_unlock(&sem->rwbase, TASK_NORMAL);
}
static inline void __sched __down_write(struct rw_semaphore *sem)
{
rwbase_write_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
}
static inline int __sched __down_write_killable(struct rw_semaphore *sem)
{
return rwbase_write_lock(&sem->rwbase, TASK_KILLABLE);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
return rwbase_write_trylock(&sem->rwbase);
}
static inline void __up_write(struct rw_semaphore *sem)
{
rwbase_write_unlock(&sem->rwbase);
}
static inline void __downgrade_write(struct rw_semaphore *sem)
{
rwbase_write_downgrade(&sem->rwbase);
}
/* Debug stubs for the common API */
#define DEBUG_RWSEMS_WARN_ON(c, sem)
static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
struct task_struct *owner)
{
}
static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
{
int count = atomic_read(&sem->rwbase.readers);
return count < 0 && count != READER_BIAS;
}
#endif /* CONFIG_PREEMPT_RT */
/*
* lock for reading
*/
void __sched down_read(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
}
EXPORT_SYMBOL(down_read);
int __sched down_read_interruptible(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_interruptible);
int __sched down_read_killable(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_killable);
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
int down_read_trylock(struct rw_semaphore *sem)
{
int ret = __down_read_trylock(sem);
if (ret == 1)
rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
return ret;
}
EXPORT_SYMBOL(down_read_trylock);
/*
* lock for writing
*/
void __sched down_write(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}
EXPORT_SYMBOL(down_write);
/*
* lock for writing
*/
int __sched down_write_killable(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
__down_write_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_write_killable);
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
int down_write_trylock(struct rw_semaphore *sem)
{
int ret = __down_write_trylock(sem);
if (ret == 1)
rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
return ret;
}
EXPORT_SYMBOL(down_write_trylock);
/*
* release a read lock
*/
void up_read(struct rw_semaphore *sem)
{
rwsem_release(&sem->dep_map, _RET_IP_);
__up_read(sem);
}
EXPORT_SYMBOL(up_read);
/*
* release a write lock
*/
void up_write(struct rw_semaphore *sem)
{
rwsem_release(&sem->dep_map, _RET_IP_);
__up_write(sem);
}
EXPORT_SYMBOL(up_write);
/*
* downgrade write lock to read lock
*/
void downgrade_write(struct rw_semaphore *sem)
{
lock_downgrade(&sem->dep_map, _RET_IP_);
__downgrade_write(sem);
}
EXPORT_SYMBOL(downgrade_write);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
void down_read_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
}
EXPORT_SYMBOL(down_read_nested);
int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_killable_nested);
void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
{
might_sleep();
rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}
EXPORT_SYMBOL(_down_write_nest_lock);
void down_read_non_owner(struct rw_semaphore *sem)
{
might_sleep();
__down_read(sem);
/*
* The owner value for a reader-owned lock is mostly for debugging
* purpose only and is not critical to the correct functioning of
* rwsem. So it is perfectly fine to set it in a preempt-enabled
* context here.
*/
__rwsem_set_reader_owned(sem, NULL);
}
EXPORT_SYMBOL(down_read_non_owner);
void down_write_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}
EXPORT_SYMBOL(down_write_nested);
int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
__down_write_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_write_killable_nested);
void up_read_non_owner(struct rw_semaphore *sem)
{
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
__up_read(sem);
}
EXPORT_SYMBOL(up_read_non_owner);
#endif
Codebase Browser
linux