linux-kernel - Re: Revert "aio: fix aio request leak when events are reaped by user space"

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Message-ID: <20140825151156.GE20070@kvack.org>
Date:	Mon, 25 Aug 2014 11:11:56 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	"Elliott, Robert (Server Storage)" <Elliott@...com>
Cc:	Dan Aloni <dan@...nelim.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"security@...nel.org" <security@...nel.org>,
	"linux-aio@...ck.org" <linux-aio@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mateusz Guzik <mguzik@...hat.com>,
	Petr Matousek <pmatouse@...hat.com>,
	Kent Overstreet <kmo@...erainc.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: Revert "aio: fix aio request leak when events are reaped by user space"

On Mon, Aug 25, 2014 at 03:06:12PM +0000, Elliott, Robert (Server Storage) wrote:
> Using this version of the patch, I ran into this crash after 36
> hours of scsi-mq testing over the weekend.
...
> 
>         local_irq_save(flags);
>         kcpu = this_cpu_ptr(ctx->cpu);
>         kcpu->reqs_available += nr;
> 
>         while (kcpu->reqs_available >= ctx->req_batch * 2) {

This crash is not particularly useful, as that version of the patch was 
buggy and could result in reqs_available getting corrupted (ie, it could 
overflow), which could lead to the system getting stuck for a significant 
amount of time in put_reqs_available().  In other words, the crash you 
reported matches the known problem with that patch.

		-ben
-- 
"Thought is the essence of where you are now."
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