Patch "xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate()" has been added to the 6.6-stable tree

This is a note to let you know that I've just added the patch titled

    xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate()

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     xfs-use-try_cmpxchg-in-xlog_cil_insert_pcp_aggregate.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.


From [email protected] Wed Feb  5 22:41:10 2025
From: Catherine Hoang <[email protected]>
Date: Wed,  5 Feb 2025 13:40:16 -0800
Subject: xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate()
To: [email protected]
Cc: [email protected]
Message-ID: <[email protected]>

From: Uros Bizjak <[email protected]>

commit 20195d011c840b01fa91a85ebcd099ca95fbf8fc upstream.

Use !try_cmpxchg instead of cmpxchg (*ptr, old, new) != old in
xlog_cil_insert_pcp_aggregate().  x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg.

Also, try_cmpxchg implicitly assigns old *ptr value to "old" when
cmpxchg fails. There is no need to re-read the value in the loop.

Note that the value from *ptr should be read using READ_ONCE to
prevent the compiler from merging, refetching or reordering the read.

No functional change intended.

Signed-off-by: Uros Bizjak <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Chandan Babu R <[email protected]>
Cc: Darrick J. Wong <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>
Signed-off-by: Catherine Hoang <[email protected]>
Acked-by: Darrick J. Wong <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 fs/xfs/xfs_log_cil.c |   11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -156,7 +156,6 @@ xlog_cil_insert_pcp_aggregate(
 	struct xfs_cil		*cil,
 	struct xfs_cil_ctx	*ctx)
 {
-	struct xlog_cil_pcp	*cilpcp;
 	int			cpu;
 	int			count = 0;
 
@@ -171,13 +170,11 @@ xlog_cil_insert_pcp_aggregate(
 	 * structures that could have a nonzero space_used.
 	 */
 	for_each_cpu(cpu, &ctx->cil_pcpmask) {
-		int	old, prev;
+		struct xlog_cil_pcp	*cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
+		int			old = READ_ONCE(cilpcp->space_used);
 
-		cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
-		do {
-			old = cilpcp->space_used;
-			prev = cmpxchg(&cilpcp->space_used, old, 0);
-		} while (old != prev);
+		while (!try_cmpxchg(&cilpcp->space_used, &old, 0))
+			;
 		count += old;
 	}
 	atomic_add(count, &ctx->space_used);


Patches currently in stable-queue which might be from [email protected] are

queue-6.6/xfs-return-bool-from-xfs_attr3_leaf_add.patch
queue-6.6/xfs-fix-a-sloppy-memory-handling-bug-in-xfs_iroot_realloc.patch
queue-6.6/xfs-streamline-xfs_filestream_pick_ag.patch
queue-6.6/xfs-merge-xfs_attr_leaf_try_add-into-xfs_attr_leaf_addname.patch
queue-6.6/xfs-don-t-free-cowblocks-from-under-dirty-pagecache-on-unshare.patch
queue-6.6/xfs-pass-the-exact-range-to-initialize-to-xfs_initialize_perag.patch
queue-6.6/xfs-assert-a-valid-limit-in-xfs_rtfind_forw.patch
queue-6.6/xfs-don-t-use-__gfp_retry_mayfail-in-xfs_initialize_perag.patch
queue-6.6/xfs-use-try_cmpxchg-in-xlog_cil_insert_pcp_aggregate.patch
queue-6.6/xfs-don-t-ifdef-around-the-exact-minlen-allocations.patch
queue-6.6/xfs-reduce-unnecessary-searches-when-searching-for-the-best-extents.patch
queue-6.6/xfs-validate-inumber-in-xfs_iget.patch
queue-6.6/xfs-support-lowmode-allocations-in-xfs_bmap_exact_minlen_extent_alloc.patch
queue-6.6/xfs-skip-background-cowblock-trims-on-inodes-open-for-write.patch
queue-6.6/xfs-remove-empty-declartion-in-header-file.patch
queue-6.6/xfs-fold-xfs_bmap_alloc_userdata-into-xfs_bmapi_allocate.patch
queue-6.6/xfs-update-the-file-system-geometry-after-recoverying-superblock-buffers.patch
queue-6.6/xfs-call-xfs_bmap_exact_minlen_extent_alloc-from-xfs_bmap_btalloc.patch
queue-6.6/xfs-distinguish-extra-split-from-real-enospc-from-xfs_attr_node_try_addname.patch
queue-6.6/xfs-error-out-when-a-superblock-buffer-update-reduces-the-agcount.patch
queue-6.6/xfs-update-the-pag-for-the-last-ag-at-recovery-time.patch
queue-6.6/xfs-check-for-delayed-allocations-before-setting-extsize.patch
queue-6.6/xfs-fix-a-typo.patch
queue-6.6/xfs-distinguish-extra-split-from-real-enospc-from-xfs_attr3_leaf_split.patch