diff options
| author | Mateusz Guzik <mjguzik@gmail.com> | 2024-08-06 19:28:46 +0200 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2024-08-30 08:22:33 +0200 |
| commit | 087adb4f0f91ee330446a70af899e6a996e5cc13 (patch) | |
| tree | e087a606f59ceef5add818265921dea4f587c7de | |
| parent | 215ab0d8af59cfc394fa83a702f0af21a5e126c7 (diff) | |
vfs: dodge smp_mb in break_lease and break_deleg in the common case
These inlines show up in the fast path (e.g., in do_dentry_open()) and
induce said full barrier regarding i_flctx access when in most cases the
pointer is NULL.
The pointer can be safely checked before issuing the barrier, dodging it
in most cases as a result.
It is plausible the consume fence would be sufficient, but I don't want
to go audit all callers regarding what they before calling here.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240806172846.886570-1-mjguzik@gmail.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
| -rw-r--r-- | include/linux/filelock.h | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/include/linux/filelock.h b/include/linux/filelock.h index daee999d05f3..bb44224c6676 100644 --- a/include/linux/filelock.h +++ b/include/linux/filelock.h @@ -420,28 +420,38 @@ static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl) #ifdef CONFIG_FILE_LOCKING static inline int break_lease(struct inode *inode, unsigned int mode) { + struct file_lock_context *flctx; + /* * Since this check is lockless, we must ensure that any refcounts * taken are done before checking i_flctx->flc_lease. Otherwise, we * could end up racing with tasks trying to set a new lease on this * file. */ + flctx = READ_ONCE(inode->i_flctx); + if (!flctx) + return 0; smp_mb(); - if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease)) + if (!list_empty_careful(&flctx->flc_lease)) return __break_lease(inode, mode, FL_LEASE); return 0; } static inline int break_deleg(struct inode *inode, unsigned int mode) { + struct file_lock_context *flctx; + /* * Since this check is lockless, we must ensure that any refcounts * taken are done before checking i_flctx->flc_lease. Otherwise, we * could end up racing with tasks trying to set a new lease on this * file. */ + flctx = READ_ONCE(inode->i_flctx); + if (!flctx) + return 0; smp_mb(); - if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease)) + if (!list_empty_careful(&flctx->flc_lease)) return __break_lease(inode, mode, FL_DELEG); return 0; } |