// SPDX-License-Identifier: GPL-2.0-or-later
/* vnode and volume validity verification.
*
* Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
* Written by David Howells ([email protected])
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include "internal.h"
/*
* Data validation is managed through a number of mechanisms from the server:
*
* (1) On first contact with a server (such as if it has just been rebooted),
* the server sends us a CB.InitCallBackState* request.
*
* (2) On a RW volume, in response to certain vnode (inode)-accessing RPC
* calls, the server maintains a time-limited per-vnode promise that it
* will send us a CB.CallBack request if a third party alters the vnodes
* accessed.
*
* Note that a vnode-level callbacks may also be sent for other reasons,
* such as filelock release.
*
* (3) On a RO (or Backup) volume, in response to certain vnode-accessing RPC
* calls, each server maintains a time-limited per-volume promise that it
* will send us a CB.CallBack request if the RO volume is updated to a
* snapshot of the RW volume ("vos release"). This is an atomic event
* that cuts over all instances of the RO volume across multiple servers
* simultaneously.
*
* Note that a volume-level callbacks may also be sent for other reasons,
* such as the volumeserver taking over control of the volume from the
* fileserver.
*
* Note also that each server maintains an independent time limit on an
* independent callback.
*
* (4) Certain RPC calls include a volume information record "VolSync" in
* their reply. This contains a creation date for the volume that should
* remain unchanged for a RW volume (but will be changed if the volume is
* restored from backup) or will be bumped to the time of snapshotting
* when a RO volume is released.
*
* In order to track this events, the following are provided:
*
* ->cb_v_break. A counter of events that might mean that the contents of
* a volume have been altered since we last checked a vnode.
*
* ->cb_v_check. A counter of the number of events that we've sent a
* query to the server for. Everything's up to date if this equals
* cb_v_break.
*
* ->cb_scrub. A counter of the number of regression events for which we
* have to completely wipe the cache.
*
* ->cb_ro_snapshot. A counter of the number of times that we've
* recognised that a RO volume has been updated.
*
* ->cb_break. A counter of events that might mean that the contents of a
* vnode have been altered.
*
* ->cb_expires_at. The time at which the callback promise expires or
* AFS_NO_CB_PROMISE if we have no promise.
*
* The way we manage things is:
*
* (1) When a volume-level CB.CallBack occurs, we increment ->cb_v_break on
* the volume and reset ->cb_expires_at (ie. set AFS_NO_CB_PROMISE) on the
* volume and volume's server record.
*
* (2) When a CB.InitCallBackState occurs, we treat this as a volume-level
* callback break on all the volumes that have been using that volume
* (ie. increment ->cb_v_break and reset ->cb_expires_at).
*
* (3) When a vnode-level CB.CallBack occurs, we increment ->cb_break on the
* vnode and reset its ->cb_expires_at. If the vnode is mmapped, we also
* dispatch a work item to unmap all PTEs to the vnode's pagecache to
* force reentry to the filesystem for revalidation.
*
* (4) When entering the filesystem, we call afs_validate() to check the
* validity of a vnode. This first checks to see if ->cb_v_check and
* ->cb_v_break match, and if they don't, we lock volume->cb_check_lock
* exclusively and perform an FS.FetchStatus on the vnode.
*
* After checking the volume, we check the vnode. If there's a mismatch
* between the volume counters and the vnode's mirrors of those counters,
* we lock vnode->validate_lock and issue an FS.FetchStatus on the vnode.
*
* (5) When the reply from FS.FetchStatus arrives, the VolSync record is
* parsed:
*
* (A) If the Creation timestamp has changed on a RW volume or regressed
* on a RO volume, we try to increment ->cb_scrub; if it advances on a
* RO volume, we assume "vos release" happened and try to increment
* ->cb_ro_snapshot.
*
* (B) If the Update timestamp has regressed, we try to increment
* ->cb_scrub.
*
* Note that in both of these cases, we only do the increment if we can
* cmpxchg the value of the timestamp from the value we noted before the
* op. This tries to prevent parallel ops from fighting one another.
*
* volume->cb_v_check is then set to ->cb_v_break.
*
* (6) The AFSCallBack record included in the FS.FetchStatus reply is also
* parsed and used to set the promise in ->cb_expires_at for the vnode,
* the volume and the volume's server record.
*
* (7) If ->cb_scrub is seen to have advanced, we invalidate the pagecache for
* the vnode.
*/
/*
* Check the validity of a vnode/inode and its parent volume.
*/
bool afs_check_validity(const struct afs_vnode *vnode)
{
const struct afs_volume *volume = vnode->volume;
time64_t deadline = ktime_get_real_seconds() + 10;
if (test_bit(AFS_VNODE_DELETED, &vnode->flags))
return true;
if (atomic_read(&volume->cb_v_check) != atomic_read(&volume->cb_v_break) ||
atomic64_read(&vnode->cb_expires_at) <= deadline ||
volume->cb_expires_at <= deadline ||
vnode->cb_ro_snapshot != atomic_read(&volume->cb_ro_snapshot) ||
vnode->cb_scrub != atomic_read(&volume->cb_scrub) ||
test_bit(AFS_VNODE_ZAP_DATA, &vnode->flags)) {
_debug("inval");
return false;
}
return true;
}
/*
* See if the server we've just talked to is currently excluded.
*/
static bool __afs_is_server_excluded(struct afs_operation *op, struct afs_volume *volume)
{
const struct afs_server_entry *se;
const struct afs_server_list *slist;
bool is_excluded = true;
int i;
rcu_read_lock();
slist = rcu_dereference(volume->servers);
for (i = 0; i < slist->nr_servers; i++) {
se = &slist->servers[i];
if (op->server == se->server) {
is_excluded = test_bit(AFS_SE_EXCLUDED, &se->flags);
break;
}
}
rcu_read_unlock();
return is_excluded;
}
/*
* Update the volume's server list when the creation time changes and see if
* the server we've just talked to is currently excluded.
*/
static int afs_is_server_excluded(struct afs_operation *op, struct afs_volume *volume)
{
int ret;
if (__afs_is_server_excluded(op, volume))
return 1;
set_bit(AFS_VOLUME_NEEDS_UPDATE, &volume->flags);
ret = afs_check_volume_status(op->volume, op);
if (ret < 0)
return ret;
return __afs_is_server_excluded(op, volume);
}
/*
* Handle a change to the volume creation time in the VolSync record.
*/
static int afs_update_volume_creation_time(struct afs_operation *op, struct afs_volume *volume)
{
unsigned int snap;
time64_t cur = volume->creation_time;
time64_t old = op->pre_volsync.creation;
time64_t new = op->volsync.creation;
int ret;
_enter("%llx,%llx,%llx->%llx", volume->vid, cur, old, new);
if (cur == TIME64_MIN) {
volume->creation_time = new;
return 0;
}
if (new == cur)
return 0;
/* Try to advance the creation timestamp from what we had before the
* operation to what we got back from the server. This should
* hopefully ensure that in a race between multiple operations only one
* of them will do this.
*/
if (cur != old)
return 0;
/* If the creation time changes in an unexpected way, we need to scrub
* our caches. For a RW vol, this will only change if the volume is
* restored from a backup; for a RO/Backup vol, this will advance when
* the volume is updated to a new snapshot (eg. "vos release").
*/
if (volume->type == AFSVL_RWVOL)
goto regressed;
if (volume->type == AFSVL_BACKVOL) {
if (new < old)
goto regressed;
goto advance;
}
/* We have an RO volume, we need to query the VL server and look at the
* server flags to see if RW->RO replication is in progress.
*/
ret = afs_is_server_excluded(op, volume);
if (ret < 0)
return ret;
if (ret > 0) {
snap = atomic_read(&volume->cb_ro_snapshot);
trace_afs_cb_v_break(volume->vid, snap, afs_cb_break_volume_excluded);
return ret;
}
advance:
snap = atomic_inc_return(&volume->cb_ro_snapshot);
trace_afs_cb_v_break(volume->vid, snap, afs_cb_break_for_vos_release);
volume->creation_time = new;
return 0;
regressed:
atomic_inc(&volume->cb_scrub);
trace_afs_cb_v_break(volume->vid, 0, afs_cb_break_for_creation_regress);
volume->creation_time = new;
return 0;
}
/*
* Handle a change to the volume update time in the VolSync record.
*/
static void afs_update_volume_update_time(struct afs_operation *op, struct afs_volume *volume)
{
enum afs_cb_break_reason reason = afs_cb_break_no_break;
time64_t cur = volume->update_time;
time64_t old = op->pre_volsync.update;
time64_t new = op->volsync.update;
_enter("%llx,%llx,%llx->%llx", volume->vid, cur, old, new);
if (cur == TIME64_MIN) {
volume->update_time = new;
return;
}
if (new == cur)
return;
/* If the volume update time changes in an unexpected way, we need to
* scrub our caches. For a RW vol, this will advance on every
* modification op; for a RO/Backup vol, this will advance when the
* volume is updated to a new snapshot (eg. "vos release").
*/
if (new < old)
reason = afs_cb_break_for_update_regress;
/* Try to advance the update timestamp from what we had before the
* operation to what we got back from the server. This should
* hopefully ensure that in a race between multiple operations only one
* of them will do this.
*/
if (cur == old) {
if (reason == afs_cb_break_for_update_regress) {
atomic_inc(&volume->cb_scrub);
trace_afs_cb_v_break(volume->vid, 0, reason);
}
volume->update_time = new;
}
}
static int afs_update_volume_times(struct afs_operation *op, struct afs_volume *volume)
{
int ret = 0;
if (likely(op->volsync.creation == volume->creation_time &&
op->volsync.update == volume->update_time))
return 0;
mutex_lock(&volume->volsync_lock);
if (op->volsync.creation != volume->creation_time) {
ret = afs_update_volume_creation_time(op, volume);
if (ret < 0)
goto out;
}
if (op->volsync.update != volume->update_time)
afs_update_volume_update_time(op, volume);
out:
mutex_unlock(&volume->volsync_lock);
return ret;
}
/*
* Update the state of a volume, including recording the expiration time of the
* callback promise. Returns 1 to redo the operation from the start.
*/
int afs_update_volume_state(struct afs_operation *op)
{
struct afs_server_list *slist = op->server_list;
struct afs_server_entry *se = &slist->servers[op->server_index];
struct afs_callback *cb = &op->file[0].scb.callback;
struct afs_volume *volume = op->volume;
unsigned int cb_v_break = atomic_read(&volume->cb_v_break);
unsigned int cb_v_check = atomic_read(&volume->cb_v_check);
int ret;
_enter("%llx", op->volume->vid);
if (op->volsync.creation != TIME64_MIN || op->volsync.update != TIME64_MIN) {
ret = afs_update_volume_times(op, volume);
if (ret != 0) {
_leave(" = %d", ret);
return ret;
}
}
if (op->cb_v_break == cb_v_break &&
(op->file[0].scb.have_cb || op->file[1].scb.have_cb)) {
time64_t expires_at = cb->expires_at;
if (!op->file[0].scb.have_cb)
expires_at = op->file[1].scb.callback.expires_at;
se->cb_expires_at = expires_at;
volume->cb_expires_at = expires_at;
}
if (cb_v_check < op->cb_v_break)
atomic_cmpxchg(&volume->cb_v_check, cb_v_check, op->cb_v_break);
return 0;
}
/*
* mark the data attached to an inode as obsolete due to a write on the server
* - might also want to ditch all the outstanding writes and dirty pages
*/
static void afs_zap_data(struct afs_vnode *vnode)
{
_enter("{%llx:%llu}", vnode->fid.vid, vnode->fid.vnode);
afs_invalidate_cache(vnode, 0);
/* nuke all the non-dirty pages that aren't locked, mapped or being
* written back in a regular file and completely discard the pages in a
* directory or symlink */
if (S_ISREG(vnode->netfs.inode.i_mode))
filemap_invalidate_inode(&vnode->netfs.inode, true, 0, LLONG_MAX);
else
filemap_invalidate_inode(&vnode->netfs.inode, false, 0, LLONG_MAX);
}
/*
* validate a vnode/inode
* - there are several things we need to check
* - parent dir data changes (rm, rmdir, rename, mkdir, create, link,
* symlink)
* - parent dir metadata changed (security changes)
* - dentry data changed (write, truncate)
* - dentry metadata changed (security changes)
*/
int afs_validate(struct afs_vnode *vnode, struct key *key)
{
struct afs_volume *volume = vnode->volume;
unsigned int cb_ro_snapshot, cb_scrub;
time64_t deadline = ktime_get_real_seconds() + 10;
bool zap = false, locked_vol = false;
int ret;
_enter("{v={%llx:%llu} fl=%lx},%x",
vnode->fid.vid, vnode->fid.vnode, vnode->flags,
key_serial(key));
if (afs_check_validity(vnode))
return test_bit(AFS_VNODE_DELETED, &vnode->flags) ? -ESTALE : 0;
ret = down_write_killable(&vnode->validate_lock);
if (ret < 0)
goto error;
if (test_bit(AFS_VNODE_DELETED, &vnode->flags)) {
ret = -ESTALE;
goto error_unlock;
}
/* Validate a volume after the v_break has changed or the volume
* callback expired. We only want to do this once per volume per
* v_break change. The actual work will be done when parsing the
* status fetch reply.
*/
if (volume->cb_expires_at <= deadline ||
atomic_read(&volume->cb_v_check) != atomic_read(&volume->cb_v_break)) {
ret = mutex_lock_interruptible(&volume->cb_check_lock);
if (ret < 0)
goto error_unlock;
locked_vol = true;
}
cb_ro_snapshot = atomic_read(&volume->cb_ro_snapshot);
cb_scrub = atomic_read(&volume->cb_scrub);
if (vnode->cb_ro_snapshot != cb_ro_snapshot ||
vnode->cb_scrub != cb_scrub)
unmap_mapping_pages(vnode->netfs.inode.i_mapping, 0, 0, false);
if (vnode->cb_ro_snapshot != cb_ro_snapshot ||
vnode->cb_scrub != cb_scrub ||
volume->cb_expires_at <= deadline ||
atomic_read(&volume->cb_v_check) != atomic_read(&volume->cb_v_break) ||
atomic64_read(&vnode->cb_expires_at) <= deadline
) {
ret = afs_fetch_status(vnode, key, false, NULL);
if (ret < 0) {
if (ret == -ENOENT) {
set_bit(AFS_VNODE_DELETED, &vnode->flags);
ret = -ESTALE;
}
goto error_unlock;
}
_debug("new promise [fl=%lx]", vnode->flags);
}
/* We can drop the volume lock now as. */
if (locked_vol) {
mutex_unlock(&volume->cb_check_lock);
locked_vol = false;
}
cb_ro_snapshot = atomic_read(&volume->cb_ro_snapshot);
cb_scrub = atomic_read(&volume->cb_scrub);
_debug("vnode inval %x==%x %x==%x",
vnode->cb_ro_snapshot, cb_ro_snapshot,
vnode->cb_scrub, cb_scrub);
if (vnode->cb_scrub != cb_scrub)
zap = true;
vnode->cb_ro_snapshot = cb_ro_snapshot;
vnode->cb_scrub = cb_scrub;
/* if the vnode's data version number changed then its contents are
* different */
zap |= test_and_clear_bit(AFS_VNODE_ZAP_DATA, &vnode->flags);
if (zap)
afs_zap_data(vnode);
up_write(&vnode->validate_lock);
_leave(" = 0");
return 0;
error_unlock:
if (locked_vol)
mutex_unlock(&volume->cb_check_lock);
up_write(&vnode->validate_lock);
error:
_leave(" = %d", ret);
return ret;
}
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