diff options
| author | Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | 2025-03-12 10:10:13 -0400 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-03-17 22:07:04 -0700 |
| commit | c0ebbb3841e07c4493e6fe351698806b09a87a37 (patch) | |
| tree | f52c675a383c5ad17f22f3ef99888c71ef86c5e6 /mm | |
| parent | be9258a6bf26d2272856214406721762a21aab1b (diff) | |
mm: add missing release barrier on PGDAT_RECLAIM_LOCKED unlock
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@efficios.com
Fixes: d773ed6b856a ("mm: test and set zone reclaim lock before starting reclaim")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/vmscan.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c index be00af3763b5..bbd3913e3887 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -7581,7 +7581,7 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order) 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); |