Re: request_queue use-after-free - inode_detach_wb()

From	Ilya Dryomov <idryomov@gmail.com>
Newsgroups	linux.kernel
Subject	Re: request_queue use-after-free - inode_detach_wb()
Date	2015-11-19 23:00 +0100
Message-ID	<qwFpg-6AK-31@gated-at.bofh.it> (permalink)
References	(2 earlier) <qwcGC-4D5-15@gated-at.bofh.it> <qwcZY-4Lu-27@gated-at.bofh.it> <qwd9E-4Pa-27@gated-at.bofh.it> <qwEtb-5WV-11@gated-at.bofh.it> <qwEMx-6ku-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Thu, Nov 19, 2015 at 10:18 PM, Tejun Heo <tj@kernel.org> wrote:
> Hello, Ilya.
>
> On Thu, Nov 19, 2015 at 09:56:21PM +0100, Ilya Dryomov wrote:
>> > Yes, that's where *I* think we should be headed.  Stuff in lower
>> > layers should stick around while upper layer things are around
>>
>> I think the fundamental problem is the embedding of bdi in the queue.
>> The lifetime rules (or, rather, expectations) for the two seem to be
>> completely different and, while used together, they belong to different
>> subsystems.  Even if we find a way to fix this particular race, there
>> is a good chance someone will reintroduce it in the future, perhaps in
>> a more subtle way.
>
> You're right.  This is nasty.  Hmmm... the root problem is that beyond
> the last __blkdev_put() the bdev and disk don't really have anything
> to do with each other but the bdev is still pointing to it.  We are
> already guaranteeing that the underlying disk hangs around while there
> are bdevs associated with it.
>
> We already know that the bdev is idle once bd_openers hits zero and
> the inode gets flushed, so at that point, the problem is bdev's
> inode->i_wb is still pointing to something that the bdev doesn't have
> anything to do with.  So, can we do inode_detach_wb() after flushing
> the inode?

Detaching the inode earlier is what I suggested in the first email, but
I didn't know if this kind of special casing was OK.  I'll try it out.

Thanks,

                Ilya
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Thread

Re: request_queue use-after-free - inode_detach_wb() Tejun Heo <tj@kernel.org> - 2015-11-17 22:00 +0100
  Re: request_queue use-after-free - inode_detach_wb() Ilya Dryomov <idryomov@gmail.com> - 2015-11-18 16:20 +0100
    Re: request_queue use-after-free - inode_detach_wb() Tejun Heo <tj@kernel.org> - 2015-11-18 16:40 +0100
      Re: request_queue use-after-free - inode_detach_wb() Ilya Dryomov <idryomov@gmail.com> - 2015-11-18 16:50 +0100
        Re: request_queue use-after-free - inode_detach_wb() Tejun Heo <tj@kernel.org> - 2015-11-18 17:00 +0100
        Re: request_queue use-after-free - inode_detach_wb() Ilya Dryomov <idryomov@gmail.com> - 2015-11-19 22:00 +0100
          Re: request_queue use-after-free - inode_detach_wb() Tejun Heo <tj@kernel.org> - 2015-11-19 22:20 +0100
            Re: request_queue use-after-free - inode_detach_wb() Ilya Dryomov <idryomov@gmail.com> - 2015-11-19 23:00 +0100
              Re: request_queue use-after-free - inode_detach_wb() Tejun Heo <tj@kernel.org> - 2015-11-19 23:20 +0100

csiph-web