4.4-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
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 call_rcu_sched().
Fixes: 267239116987 ("mm, powerpc: move the RCU page-table freeing into generic code") Reported-by: Will Deacon will.deacon@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Acked-by: Rik van Riel riel@surriel.com Acked-by: Will Deacon will.deacon@arm.com Cc: Nicholas Piggin npiggin@gmail.com Cc: David Miller davem@davemloft.net Cc: Martin Schwidefsky schwidefsky@de.ibm.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: stable@kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/memory.c | 9 --------- 1 file changed, 9 deletions(-)
--- a/mm/memory.c +++ b/mm/memory.c @@ -361,15 +361,6 @@ void tlb_remove_table(struct mmu_gather { struct mmu_table_batch **batch = &tlb->batch;
- /* - * 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) {