[PATCH v3 6/8] super: Use acquire for SB_BORN check in super_cache_count()

[Jinjie Ruan]

The active SB_BORN check in super_cache_count() pairs with the
smp_store_release() in super_wake() when publishing a newly initialized
superblock.

Replace the historical independent smp_rmb() barrier with an acquire load
on sb->s_flags via super_flags(). This expresses the publish-subscribe
pattern more clearly and allows weakly-ordered architectures like arm64
to utilize efficient native instructions (e.g., LDAR) instead of a full
one-way barrier.

Also remove the outdated memory barrier comment in super_cache_count(),
as the underlying super_flags() implementation already self-documents
the matched smp_store_release() in super_wake().

Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Assisted-by: Gemini:Gemini-3.1
Assisted-by: DeepSeek:DeepSeek-V3
Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
---
 fs/super.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 05e443173038..caa6189e4057 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -267,12 +267,10 @@ static unsigned long super_cache_count(struct shrinker *shrink,
 	 * However, if we are currently mounting the superblock, the underlying
 	 * filesystem might be in a state of partial construction and hence it
 	 * is dangerous to access it.  super_trylock_shared() uses a SB_BORN check
-	 * to avoid this situation, so do the same here. The memory barrier is
-	 * matched with the one in mount_fs() as we don't hold locks here.
+	 * to avoid this situation, so do the same here.
 	 */
-	if (!(sb->s_flags & SB_BORN))
+	if (!super_flags(sb, SB_BORN))
 		return 0;
-	smp_rmb();
 
 	if (sb->s_op && sb->s_op->nr_cached_objects &&
 	    super_fs_objects_eligible(sc))
-- 
2.34.1