The patch titled
Subject: mm: migrate: fix barriers around tlb_flush_pending
has been added to the -mm tree. Its filename is
mm-migrate-fix-barriers-around-tlb_flush_pending.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-migrate-fix-barriers-around-tlb_flush_pending.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-migrate-fix-barriers-around-tlb_flush_pending.patch
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From: Nadav Amit <namit@xxxxxxxxxx>
Subject: mm: migrate: fix barriers around tlb_flush_pending
Reading tlb_flush_pending while the page-table lock is taken does not
require a barrier, since the lock/unlock already acts as a barrier.
Removing the barrier in mm_tlb_flush_pending() to address this issue.
However, migrate_misplaced_transhuge_page() calls mm_tlb_flush_pending()
while the page-table lock is already released, which may present a problem
on architectures with weak memory model (PPC). To deal with this case, a
new parameter is added to mm_tlb_flush_pending() to indicate if it is read
without the page-table lock taken, and calling smp_mb__after_unlock_lock()
in this case.
Link: http://lkml.kernel.org/r/20170802000818.4760-3-namit@xxxxxxxxxx
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jeff Dike <jdike@xxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm_types.h | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff -puN include/linux/mm_types.h~mm-migrate-fix-barriers-around-tlb_flush_pending include/linux/mm_types.h
--- a/include/linux/mm_types.h~mm-migrate-fix-barriers-around-tlb_flush_pending
+++ a/include/linux/mm_types.h
@@ -526,12 +526,12 @@ static inline cpumask_t *mm_cpumask(stru
/*
* Memory barriers to keep this state in sync are graciously provided by
* the page table locks, outside of which no page table modifications happen.
- * The barriers below prevent the compiler from re-ordering the instructions
- * around the memory barriers that are already present in the code.
+ * The barriers are used to ensure the order between tlb_flush_pending updates,
+ * which happen while the lock is not taken, and the PTE updates, which happen
+ * while the lock is taken, are serialized.
*/
static inline bool mm_tlb_flush_pending(struct mm_struct *mm)
{
- barrier();
return atomic_read(&mm->tlb_flush_pending) > 0;
}
@@ -554,7 +554,13 @@ static inline void inc_tlb_flush_pending
/* Clearing is done after a TLB flush, which also provides a barrier. */
static inline void dec_tlb_flush_pending(struct mm_struct *mm)
{
- barrier();
+ /*
+ * Guarantee that the tlb_flush_pending does not not leak into the
+ * critical section, since we must order the PTE change and changes to
+ * the pending TLB flush indication. We could have relied on TLB flush
+ * as a memory barrier, but this behavior is not clearly documented.
+ */
+ smp_mb__before_atomic();
atomic_dec(&mm->tlb_flush_pending);
}
#else
_
Patches currently in -mm which might be from namit@xxxxxxxxxx are
mm-migrate-fix-barriers-around-tlb_flush_pending.patch
revert-mm-numa-defer-tlb-flush-for-thp-migration-as-long-as-possible.patch
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