On Wed, 2023-08-23 at 17:33 -0400, Alexander Aring wrote:
> 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.
>
> The introducing of the new B_PENDING_CALLBACK nlm_block flag will handle
> async lock requests on a pending lock requests as a retry on the caller
> level to hit the -EAGAIN case.
>
> Signed-off-by: Alexander Aring <aahri...@redhat.com>
> ---
> fs/lockd/svclock.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
> index aa4174fbaf5b..3b158446203b 100644
> --- a/fs/lockd/svclock.c
> +++ b/fs/lockd/svclock.c
> @@ -546,6 +546,9 @@ 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)
> @@ -557,9 +560,12 @@ 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:
> @@ -570,17 +576,16 @@ 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);
Reviewed-by: Jeff Layton <jlay...@kernel.org>
