The quilt patch titled
Subject: mm: add missing release barrier on PGDAT_RECLAIM_LOCKED unlock
has been removed from the -mm tree. Its filename was
mm-add-missing-release-barrier-on-pgdat_reclaim_locked-unlock.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Subject: mm: add missing release barrier on PGDAT_RECLAIM_LOCKED unlock
Date: Wed, 12 Mar 2025 10:10:13 -0400
The PGDAT_RECLAIM_LOCKED bit is used to provide mutual exclusion of node
reclaim for struct pglist_data using a single bit.
It is "locked" with a test_and_set_bit (similarly to a try lock) which
provides full ordering with respect to loads and stores done within
__node_reclaim().
It is "unlocked" with clear_bit(), which does not provide any ordering
with respect to loads and stores done before clearing the bit.
The lack of clear_bit() memory ordering with respect to stores within
__node_reclaim() can cause a subsequent CPU to fail to observe stores from
a prior node reclaim. This is not an issue in practice on TSO (e.g.
x86), but it is an issue on weakly-ordered architectures (e.g. arm64).
Fix this by using clear_bit_unlock rather than clear_bit to clear
PGDAT_RECLAIM_LOCKED with a release memory ordering semantic.
This provides stronger memory ordering (release rather than relaxed).
Link: https://lkml.kernel.org/r/20250312141014.129725-1-mathieu.desnoyers@xxxxxxxxxxxx
Fixes: d773ed6b856a ("mm: test and set zone reclaim lock before starting reclaim")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Parri <parri.andrea@xxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Jade Alglave <j.alglave@xxxxxxxxx>
Cc: Luc Maranget <luc.maranget@xxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/vmscan.c~mm-add-missing-release-barrier-on-pgdat_reclaim_locked-unlock
+++ a/mm/vmscan.c
@@ -7581,7 +7581,7 @@ int node_reclaim(struct pglist_data *pgd
return NODE_RECLAIM_NOSCAN;
ret = __node_reclaim(pgdat, gfp_mask, order);
- clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
+ clear_bit_unlock(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
if (ret)
count_vm_event(PGSCAN_ZONE_RECLAIM_SUCCESS);
_
Patches currently in -mm which might be from mathieu.desnoyers@xxxxxxxxxxxx are
