| From | Kamal Mostafa <> | Subject | [PATCH 3.13 131/259] aio: protect reqs_available updates from changes in interrupt handlers | Date | Fri, 8 Aug 2014 13:39:14 -0700 |
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3.13.11.6 -stable review patch. If anyone has any objections, please let me know.
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From: Benjamin LaHaise <bcrl@kvack.org>
commit 263782c1c95bbddbb022dc092fd89a36bb8d5577 upstream.
As of commit f8567a3845ac05bb28f3c1b478ef752762bd39ef it is now possible to have put_reqs_available() called from irq context. While put_reqs_available() is per cpu, it did not protect itself from interrupts on the same CPU. This lead to aio_complete() corrupting the available io requests count when run under a heavy O_DIRECT workloads as reported by Robert Elliott. Fix this by disabling irq updates around the per cpu batch updates of reqs_available.
Many thanks to Robert and folks for testing and tracking this down.
Reported-by: Robert Elliot <Elliott@hp.com> Tested-by: Robert Elliot <Elliott@hp.com> Signed-off-by: Benjamin LaHaise <bcrl@kvack.org> Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@infradead.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- fs/aio.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/fs/aio.c b/fs/aio.c index 19e7d95..a0d9e43 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -816,16 +816,20 @@ void exit_aio(struct mm_struct *mm) static void put_reqs_available(struct kioctx *ctx, unsigned nr) { struct kioctx_cpu *kcpu; + unsigned long flags; preempt_disable(); kcpu = this_cpu_ptr(ctx->cpu); + local_irq_save(flags); kcpu->reqs_available += nr; + while (kcpu->reqs_available >= ctx->req_batch * 2) { kcpu->reqs_available -= ctx->req_batch; atomic_add(ctx->req_batch, &ctx->reqs_available); } + local_irq_restore(flags); preempt_enable(); } @@ -833,10 +837,12 @@ static bool get_reqs_available(struct kioctx *ctx) { struct kioctx_cpu *kcpu; bool ret = false; + unsigned long flags; preempt_disable(); kcpu = this_cpu_ptr(ctx->cpu); + local_irq_save(flags); if (!kcpu->reqs_available) { int old, avail = atomic_read(&ctx->reqs_available); @@ -855,6 +861,7 @@ static bool get_reqs_available(struct kioctx *ctx) ret = true; kcpu->reqs_available--; out: + local_irq_restore(flags); preempt_enable(); return ret; } -- 1.9.1
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