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From: Luis Chamberlain <mcgrof@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org,
	gregkh@linuxfoundation.org, rostedt@goodmis.org,
	mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com,
	nstange@suse.de, akpm@linux-foundation.org, mhocko@suse.com,
	yukuai3@huawei.com, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, Omar Sandoval <osandov@fb.com>,
	Hannes Reinecke <hare@suse.com>, Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 3/5] blktrace: refcount the request_queue during ioctl
Date: Wed, 15 Apr 2020 12:34:34 +0000
Message-ID: <20200415123434.GU11244@42.do-not-panic.com> (raw)
In-Reply-To: <20200415071425.GA21099@infradead.org>

On Wed, Apr 15, 2020 at 12:14:25AM -0700, Christoph Hellwig wrote:
> On Wed, Apr 15, 2020 at 06:16:49AM +0000, Luis Chamberlain wrote:
> > The BLKTRACESETUP above works on request_queue which later
> > LOOP_CTL_DEL races on and sweeps the debugfs dir underneath us.
> > If you use this commit alone though, this doesn't fix the race issue
> > however, and that's because of both still the debugfs_lookup() use
> > and that we're still using asynchronous removal at this point.
> > 
> > refcounting will just ensure we don't take the request_queue underneath
> > our noses.
> > 
> > Should I just add this to the commit log?
> 
> That sounds much more useful than the trace.
> 
> Btw, Isn't blk_get_queue racy as well?  Shouldn't we check
> blk_queue_dying after getting the reference and undo it if the queue is
> indeeed dying?

Yes that race should be possible:

bool blk_get_queue(struct request_queue *q)                                     
{                                                                               
	if (likely(!blk_queue_dying(q))) {
       ----------> we can get the queue to go dying here <---------
		__blk_get_queue(q);
		return true;
	}                                                                       

	return false;
}                                                                               
EXPORT_SYMBOL(blk_get_queue);

I'll pile up a fix. I've also considered doing a full review of callers
outside of the core block layer using it, and maybe just unexporting
this. It was originally exported due to commit d86e0e83b ("block: export
blk_{get,put}_queue()") to fix a scsi bug, but I can't find such
respective fix. I suspec that using bdgrab()/bdput() seems more likely
what drivers should be using. That would allow us to keep this
functionality internal.

Think that's worthy review?

  Luis

  reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-14  4:18 [PATCH 0/5] blktrace: fix use after free Luis Chamberlain
2020-04-14  4:18 ` [PATCH 1/5] block: move main block debugfs initialization to its own file Luis Chamberlain
2020-04-14  7:35   ` Greg KH
2020-04-15  2:44   ` Bart Van Assche
2020-04-14  4:18 ` [PATCH 2/5] blktrace: fix debugfs use after free Luis Chamberlain
2020-04-14  7:37   ` Greg KH
2020-04-14 15:38   ` Christoph Hellwig
2020-04-15  2:46   ` Bart Van Assche
2020-04-15 17:38   ` Eric Sandeen
2020-04-15 21:48     ` Bart Van Assche
2020-04-16  0:56     ` Luis Chamberlain
2020-04-16  1:02       ` Eric Sandeen
2020-04-16  1:20         ` Luis Chamberlain
2020-04-16  2:10   ` Ming Lei
2020-04-16  5:25     ` Luis Chamberlain
2020-04-16  5:47       ` Ming Lei
2020-04-16  6:09         ` Ming Lei
2020-04-16  6:22           ` Luis Chamberlain
2020-04-16  6:20         ` Luis Chamberlain
2020-04-16  6:28           ` Ming Lei
2020-04-17  4:09             ` Luis Chamberlain
2020-04-14  4:19 ` [PATCH 3/5] blktrace: refcount the request_queue during ioctl Luis Chamberlain
2020-04-14 15:40   ` Christoph Hellwig
2020-04-15  6:16     ` Luis Chamberlain
2020-04-15  7:14       ` Christoph Hellwig
2020-04-15 12:34         ` Luis Chamberlain [this message]
2020-04-15 12:39           ` Christoph Hellwig
2020-04-15 13:25             ` Luis Chamberlain
2020-04-15 14:18           ` Bart Van Assche
2020-04-16  1:12             ` Luis Chamberlain
2020-04-16  3:43               ` Bart Van Assche
2020-04-16  5:29                 ` Luis Chamberlain
2020-04-15 14:45       ` Bart Van Assche
2020-04-16  1:17         ` Luis Chamberlain
2020-04-16  2:31   ` Ming Lei
2020-04-16  5:36     ` Luis Chamberlain
2020-04-14  4:19 ` [PATCH 4/5] mm/swapfile: refcount block and queue before using blkcg_schedule_throttle() Luis Chamberlain
2020-04-14 15:44   ` Christoph Hellwig
2020-04-15  5:42     ` Luis Chamberlain
2020-04-15  7:27       ` Christoph Hellwig
2020-04-15  7:34         ` Christoph Hellwig
2020-04-15 13:19           ` Luis Chamberlain
2020-04-16  6:10             ` Christoph Hellwig
2020-04-16  6:22   ` Ming Lei
2020-04-16  6:25     ` Luis Chamberlain
2020-04-16  6:34       ` Ming Lei
2020-04-14  4:19 ` [PATCH 5/5] block: revert back to synchronous request_queue removal Luis Chamberlain
2020-04-14 15:47   ` Christoph Hellwig
2020-04-14 20:58     ` Luis Chamberlain
2020-04-15  6:46       ` Christoph Hellwig
2020-04-15 13:20         ` Luis Chamberlain
2020-04-16  2:36   ` Ming Lei
2020-04-14  7:38 ` [PATCH 0/5] blktrace: fix use after free Greg KH

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