[PATCH 3.16 159/328] mm/tlb: Remove tlb_remove_table() non-concurrent condition

From: Ben Hutchings
Date: Sun Dec 09 2018 - 17:23:10 EST

3.16.62-rc1 review patch. If anyone has any objections, please let me know.


From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

commit a6f572084fbee8b30f91465f4a085d7a90901c57 upstream.

Will noted that only checking mm_users is incorrect; we should also
check mm_count in order to cover CPUs that have a lazy reference to
this mm (and could do speculative TLB operations).

If removing this turns out to be a performance issue, we can
re-instate a more complete check, but in tlb_table_flush() eliding the

Fixes: 267239116987 ("mm, powerpc: move the RCU page-table freeing into generic code")
Reported-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
mm/memory.c | 9 ---------
1 file changed, 9 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -359,15 +359,6 @@ void tlb_remove_table(struct mmu_gather

tlb->need_flush = 1;

- /*
- * When there's less then two users of this mm there cannot be a
- * concurrent page-table walk.
- */
- if (atomic_read(&tlb->mm->mm_users) < 2) {
- __tlb_remove_table(table);
- return;
- }
if (*batch == NULL) {
*batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
if (*batch == NULL) {