From: Jeff Moyer <jmoyer@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>,
viro@zeniv.linux.org.uk, jack@suse.cz, dmonakhov@openvz.org,
linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>,
Mikulas Patocka <mpatocka@redhat.com>
Subject: Re: [PATCH] aio: fix a use after free (and fix freeze protection of aio writes)
Date: Mon, 17 Oct 2016 16:04:00 -0400 [thread overview]
Message-ID: <x491szevj2n.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <20161017195454.GA3568@worktop.programming.kicks-ass.net> (Peter Zijlstra's message of "Mon, 17 Oct 2016 21:54:54 +0200")
Peter Zijlstra <peterz@infradead.org> writes:
> On Mon, Oct 17, 2016 at 03:40:24PM -0400, Jeff Moyer wrote:
>> Christoph Hellwig <hch@lst.de> writes:
>>
>> > On Mon, Oct 17, 2016 at 02:19:47PM -0400, Jeff Moyer wrote:
>> >> This ends up being a call to __sb_end_write:
>> >>
>> >> void __sb_end_write(struct super_block *sb, int level)
>> >> {
>> >> percpu_up_read(sb->s_writers.rw_sem + level-1);
>> >> }
>> >>
>> >> Nothing guarantees that submission and completion happen on the same
>> >> CPU. Is this safe?
>> >
>> > Good point. From my reading of the percpu_rwsem implementation it
>> > is not safe to release it from a different CPU. Which makes me
>> > wonder how we can protect aio writes properly here..
>>
>> Could we just change percpu_rw_semaphore->read_count to be a signed
>> integer? The down_write path sums up the counters from all cpus...
>
> To what point?
Duh, nevermind. You're right, it should work as-is.
-Jeff
next prev parent reply other threads:[~2016-10-17 20:04 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-16 5:51 [PATCH] aio: fix a use after free (and fix freeze protection of aio writes) Christoph Hellwig
2016-10-17 18:19 ` Jeff Moyer
2016-10-17 18:55 ` Christoph Hellwig
2016-10-17 19:40 ` Jeff Moyer
2016-10-17 19:54 ` Peter Zijlstra
2016-10-17 20:04 ` Jeff Moyer [this message]
2016-10-17 20:04 ` Christoph Hellwig
2016-10-17 19:54 ` Peter Zijlstra
2016-10-17 20:05 ` Jeff Moyer
2016-10-24 6:36 ` Christoph Hellwig
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