Commit 04d1d58c authored Aug 22, 2018 by Peter Zijlstra Committed by Greg Kroah-Hartman Sep 09, 2018

mm/tlb: Remove tlb_remove_table() non-concurrent condition



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: 26723911 ("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>

parent 7c439bc2

mm/memory.c

+0 −9

Original line number	Diff line number	Diff line
		@@ -373,15 +373,6 @@ void tlb_remove_table(struct mmu_gather tlb, void table)
		{
		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) {