Re: Linux 3.19-rc3

Mark Langsdorf
2015-01-12T13:23:05Z

On 01/12/2015 06:42 AM, Will Deacon wrote:
> On Sat, Jan 10, 2015 at 07:51:03PM +0000, Linus Torvalds wrote:
>> I can revert the commit that causes problems, but considering the
>> performance impact on x86 (it would be a regression since 3.18), I
>> would *really* like to fix the arm64 problem instead. So I'll wait
>> with the revert for at least a week, I think, hoping that the arm64
>> people figure this out. Sound reasonable?
>
> Sure. I've put together the following patch which:
>
> (1) Uses tlb->end != 0 only as the predicate for TLB invalidation
>
> (2) Uses tlb->local.nr as the predicate for page freeing in
> tlb_flush_mmu_free
>
> (3) Ensures tlb->end != 0 for the fullmm case (I think this was a
> benign change introduced by my original patch, but this puts us
> back to 3.18 behaviour)
>
> Since this effectively reverts f045bbb9fa1b, I've added Dave to Cc. It
> should fix the leak without reintroducing the performance regression.
>
> Linus: this moves the tlb->end check back into tlb_flush_mmu_tlbonly.
> How much do you hate that?
>
> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> index 08848050922e..db284bff29dc 100644
> --- a/include/asm-generic/tlb.h
> +++ b/include/asm-generic/tlb.h
> @@ -136,8 +136,12 @@ static inline void __tlb_adjust_range(struct mmu_gather *tlb,
>
> static inline void __tlb_reset_range(struct mmu_gather *tlb)
> {
> - tlb->start = TASK_SIZE;
> - tlb->end = 0;
> + if (tlb->fullmm) {
> + tlb->start = tlb->end = ~0;
> + } else {
> + tlb->start = TASK_SIZE;
> + tlb->end = 0;
> + }
> }
>
> /*
> diff --git a/mm/memory.c b/mm/memory.c
> index c6565f00fb38..54f3a9b00956 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -235,6 +235,9 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned long
>
> static void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
> {
> + if (!tlb->end)
> + return;
> +
> tlb_flush(tlb);
> mmu_notifier_invalidate_range(tlb->mm, tlb->start, tlb->end);
> #ifdef CONFIG_HAVE_RCU_TABLE_FREE
> @@ -247,7 +250,7 @@ static void tlb_flush_mmu_free(struct mmu_gather *tlb)
> {
> struct mmu_gather_batch *batch;
>
> - for (batch = &tlb->local; batch; batch = batch->next) {
> + for (batch = &tlb->local; batch && batch->nr; batch = batch->next) {
> free_pages_and_swap_cache(batch->pages, batch->nr);
> batch->nr = 0;
> }
> @@ -256,9 +259,6 @@ static void tlb_flush_mmu_free(struct mmu_gather *tlb)
>
> void tlb_flush_mmu(struct mmu_gather *tlb)
> {
> - if (!tlb->end)
> - return;
> -
> tlb_flush_mmu_tlbonly(tlb);
> tlb_flush_mmu_free(tlb);
> }
>

This fixes the originally reported problem. I have no opinion on
moving the tlb->end check back into tlb_flush_mmu_tlbonly.

Tested-by: Mark Langsdorf <mlangsdo@redhat.com>