From 8cf9a01edc216b16b5839eb793ac544d2c97ce97 Mon Sep 17 00:00:00 2001 From: Benjamin Coddington Date: Wed, 11 Sep 2024 15:42:57 -0400 Subject: [PATCH] fs: Introduce FOP_ASYNC_LOCK Some lock managers (NLM, kNFSD) fastidiously avoid blocking their kernel threads while servicing blocking locks. If a filesystem supports asynchronous lock requests those lock managers can use notifications to quickly inform clients they have acquired a file lock. Historically, only posix_lock_file() was capable of supporting asynchronous locks so the check for support was simply file_operations->lock(), but with recent changes in DLM, both GFS2 and OCFS2 also support asynchronous locks and have started signalling their support with EXPORT_OP_ASYNC_LOCK. We recently noticed that those changes dropped the checks for whether a filesystem simply defaults to posix_lock_file(), so async lock notifications have not been attempted for NLM and NFSv4.1+ for most filesystems. While trying to fix this it has become clear that testing both the export flag combined with testing ->lock() creates quite a layering mess. It seems appropriate to signal support with a fop_flag. Add FOP_ASYNC_LOCK so that filesystems with ->lock() can signal their capability to handle lock requests asynchronously. Add a helper for lock managers to properly test that support. Signed-off-by: Benjamin Coddington Link: https://lore.kernel.org/r/3330d5a324abe2ce9c1dafe89cacdc6db41945d1.1726083391.git.bcodding@redhat.com Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner --- include/linux/filelock.h | 5 +++++ include/linux/fs.h | 2 ++ 2 files changed, 7 insertions(+) diff --git a/include/linux/filelock.h b/include/linux/filelock.h index daee999d05f39..58c1120a8253d 100644 --- a/include/linux/filelock.h +++ b/include/linux/filelock.h @@ -180,6 +180,11 @@ static inline void locks_wake_up(struct file_lock *fl) wake_up(&fl->c.flc_wait); } +static inline bool locks_can_async_lock(const struct file_operations *fops) +{ + return !fops->lock || fops->fop_flags & FOP_ASYNC_LOCK; +} + /* fs/locks.c */ void locks_free_lock_context(struct inode *inode); void locks_free_lock(struct file_lock *fl); diff --git a/include/linux/fs.h b/include/linux/fs.h index 6ca11e241a249..78221ae589d9d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2074,6 +2074,8 @@ struct file_operations { #define FOP_DIO_PARALLEL_WRITE ((__force fop_flags_t)(1 << 3)) /* Contains huge pages */ #define FOP_HUGE_PAGES ((__force fop_flags_t)(1 << 4)) +/* Supports asynchronous lock callbacks */ +#define FOP_ASYNC_LOCK ((__force fop_flags_t)(1 << 5)) /* Wrap a directory iterator that needs exclusive inode access */ int wrap_directory_iterator(struct file *, struct dir_context *,