[PATCH] fs/affs: Replace binary semaphores with mutexes

[PATCH] fs/affs: Replace binary semaphores with mutexes

[Davidlohr Bueso]

At a slight footprint cost (24 vs 32 bytes), mutexes are more optimal
than semaphores; it's also a nicer interface for mutual exclusion,
which is why they are encouraged over binary semaphores, when possible.

For both i_link_lock and i_ext_lock (and hence i_hash_lock which I
annotated for the hash lock mapping hackery for lockdep), their semantics
imply traditional lock ownership; that is, the lock owner is the same for
both lock/unlock operations and does not run in irq context. Therefore
it is safe to convert.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
Compile tested only.

 fs/affs/affs.h  | 16 ++++++++--------
 fs/affs/super.c |  4 ++--
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/affs/affs.h b/fs/affs/affs.h
index a92eb6ae2ae2..a755bef7c4c7 100644
--- a/fs/affs/affs.h
+++ b/fs/affs/affs.h
@@ -43,8 +43,8 @@ struct affs_ext_key {
  */
 struct affs_inode_info {
 	atomic_t i_opencnt;
-	struct semaphore i_link_lock;		/* Protects internal inode access. */
-	struct semaphore i_ext_lock;		/* Protects internal inode access. */
+	struct mutex i_link_lock;		/* Protects internal inode access. */
+	struct mutex i_ext_lock;		/* Protects internal inode access. */
 #define i_hash_lock i_ext_lock
 	u32	 i_blkcnt;			/* block count */
 	u32	 i_extcnt;			/* extended block count */
@@ -293,30 +293,30 @@ affs_adjust_bitmapchecksum(struct buffer_head *bh, u32 val)
 static inline void
 affs_lock_link(struct inode *inode)
 {
-	down(&AFFS_I(inode)->i_link_lock);
+	mutex_lock(&AFFS_I(inode)->i_link_lock);
 }
 static inline void
 affs_unlock_link(struct inode *inode)
 {
-	up(&AFFS_I(inode)->i_link_lock);
+	mutex_unlock(&AFFS_I(inode)->i_link_lock);
 }
 static inline void
 affs_lock_dir(struct inode *inode)
 {
-	down(&AFFS_I(inode)->i_hash_lock);
+	mutex_lock_nested(&AFFS_I(inode)->i_hash_lock, SINGLE_DEPTH_NESTING);
 }
 static inline void
 affs_unlock_dir(struct inode *inode)
 {
-	up(&AFFS_I(inode)->i_hash_lock);
+	mutex_unlock(&AFFS_I(inode)->i_hash_lock);
 }
 static inline void
 affs_lock_ext(struct inode *inode)
 {
-	down(&AFFS_I(inode)->i_ext_lock);
+	mutex_lock(&AFFS_I(inode)->i_ext_lock);
 }
 static inline void
 affs_unlock_ext(struct inode *inode)
 {
-	up(&AFFS_I(inode)->i_ext_lock);
+	mutex_unlock(&AFFS_I(inode)->i_ext_lock);
 }
diff --git a/fs/affs/super.c b/fs/affs/super.c
index cc463ae47c12..9fcff55c65af 100644
--- a/fs/affs/super.c
+++ b/fs/affs/super.c
@@ -121,8 +121,8 @@ static void init_once(void *foo)
 {
 	struct affs_inode_info *ei = (struct affs_inode_info *) foo;
 
-	sema_init(&ei->i_link_lock, 1);
-	sema_init(&ei->i_ext_lock, 1);
+	mutex_init(&ei->i_link_lock);
+	mutex_init(&ei->i_ext_lock);
 	inode_init_once(&ei->vfs_inode);
 }
 
-- 
2.16.4

Re: [PATCH] fs/affs: Replace binary semaphores with mutexes

[David Sterba]

On Sun, Oct 27, 2019 at 03:01:43PM -0700, Davidlohr Bueso wrote:
> At a slight footprint cost (24 vs 32 bytes), mutexes are more optimal
> than semaphores; it's also a nicer interface for mutual exclusion,
> which is why they are encouraged over binary semaphores, when possible.
> 
> For both i_link_lock and i_ext_lock (and hence i_hash_lock which I
> annotated for the hash lock mapping hackery for lockdep), their semantics
> imply traditional lock ownership; that is, the lock owner is the same for
> both lock/unlock operations and does not run in irq context. Therefore
> it is safe to convert.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@suse.de>

Thanks, I'll add it to affs queue.