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lockd: fix race in async lock request handling

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This patch fixes a race in async lock request handling between adding
the relevant struct nlm_block to nlm_blocked list after the request was
sent by vfs_lock_file() and nlmsvc_grant_deferred() does a lookup of the
nlm_block in the nlm_blocked list. It could be that the async request is
completed before the nlm_block was added to the list. This would end
in a -ENOENT and a kernel log message of "lockd: grant for unknown
block".

To solve this issue we add the nlm_block before the vfs_lock_file() call
to be sure it has been added when a possible nlmsvc_grant_deferred() is
called. If the vfs_lock_file() results in an case when it wouldn't be
added to nlm_blocked list, the nlm_block struct will be removed from
this list again.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Alexander Aring 2023-09-12 17:53:20 -04:00 committed by Chuck Lever
parent b743612c0a
commit afb13302aa
1 changed files with 8 additions and 3 deletions
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11
fs/lockd/svclock.c
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@ -555,6 +555,9 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
ret = nlm_lck_blocked;
goto out;
}
/* Append to list of blocked */
nlmsvc_insert_block_locked(block, NLM_NEVER);
spin_unlock(&nlm_blocked_lock);
if (!wait)
@ -566,9 +569,12 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
dprintk("lockd: vfs_lock_file returned %d\n", error);
switch (error) {
case 0:
nlmsvc_remove_block(block);
ret = nlm_granted;
goto out;
case -EAGAIN:
if (!wait)
nlmsvc_remove_block(block);
ret = async_block ? nlm_lck_blocked : nlm_lck_denied;
goto out;
case FILE_LOCK_DEFERRED:
@ -579,17 +585,16 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
ret = nlmsvc_defer_lock_rqst(rqstp, block);
goto out;
case -EDEADLK:
nlmsvc_remove_block(block);
ret = nlm_deadlock;
goto out;
default: /* includes ENOLCK */
nlmsvc_remove_block(block);
ret = nlm_lck_denied_nolocks;
goto out;
}
ret = nlm_lck_blocked;
/* Append to list of blocked */
nlmsvc_insert_block(block, NLM_NEVER);
out:
mutex_unlock(&file->f_mutex);
nlmsvc_release_block(block);