@@ -7567,11 +7567,11 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
return NODE_RECLAIM_NOSCAN;
- if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
+ if (test_and_set_bit_lock(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
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);
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 with following changes: A) Use 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). B) Use test_and_set_bit_lock rather than test_and_set_bit to test-and-set PGDAT_RECLAIM_LOCKED with an acquire memory ordering semantic. This changes the "lock" acquisition from a full barrier to an acquire memory ordering, which is weaker. The acquire semi-permeable barrier paired with the release on unlock is sufficient for this mutual exclusion use-case. Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Andrew Morton <akpm@linux-foundation.org> 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: linux-mm@kvack.org --- mm/vmscan.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)