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authorDavidlohr Bueso <dave@stgolabs.net>2017-10-03 16:15:03 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-10-03 17:54:24 -0700
commit6818600ff094ca255a7fe31838ad50c29656c3c5 (patch)
tree43ed936d9217cf7b097f8b44e55200844151e35d
parenta1b2289cef92ef0e9a92afcd2e1ea71d5bcaaf64 (diff)
downloadop-kernel-dev-6818600ff094ca255a7fe31838ad50c29656c3c5.zip
op-kernel-dev-6818600ff094ca255a7fe31838ad50c29656c3c5.tar.gz
mm,compaction: serialize waitqueue_active() checks (for real)
Andrea brought to my attention that the L->{L,S} guarantees are completely bogus for this case. I was looking at the diagram, from the offending commit, when that _is_ the race, we had the load reordered already. What we need is at least S->L semantics, thus simply use wq_has_sleeper() to serialize the call for good. Link: http://lkml.kernel.org/r/20170914175313.GB811@linux-80c1.suse Fixes: 46acef048a6 (mm,compaction: serialize waitqueue_active() checks) Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Reported-by: Andrea Parri <parri.andrea@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/compaction.c13
1 files changed, 5 insertions, 8 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index fb548e4..03d31a8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1999,17 +1999,14 @@ void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
if (pgdat->kcompactd_max_order < order)
pgdat->kcompactd_max_order = order;
- /*
- * Pairs with implicit barrier in wait_event_freezable()
- * such that wakeups are not missed in the lockless
- * waitqueue_active() call.
- */
- smp_acquire__after_ctrl_dep();
-
if (pgdat->kcompactd_classzone_idx > classzone_idx)
pgdat->kcompactd_classzone_idx = classzone_idx;
- if (!waitqueue_active(&pgdat->kcompactd_wait))
+ /*
+ * Pairs with implicit barrier in wait_event_freezable()
+ * such that wakeups are not missed.
+ */
+ if (!wq_has_sleeper(&pgdat->kcompactd_wait))
return;
if (!kcompactd_node_suitable(pgdat))
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