From: Luis Chamberlain <mcgrof@kernel.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Christoph Hellwig <hch@infradead.org>,
axboe@kernel.dk, viro@zeniv.linux.org.uk,
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: Thu, 16 Apr 2020 01:12:47 +0000 [thread overview]
Message-ID: <20200416011247.GB11244@42.do-not-panic.com> (raw)
In-Reply-To: <73332d32-b095-507f-fb2a-68460533eeb7@acm.org>
On Wed, Apr 15, 2020 at 07:18:22AM -0700, Bart Van Assche wrote:
> On 2020-04-15 05:34, Luis Chamberlain wrote:
> > On Wed, Apr 15, 2020 at 12:14:25AM -0700, Christoph Hellwig wrote:
> >> 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.
>
> blk_get_queue() prevents concurrent freeing of struct request_queue but
> does not prevent concurrent blk_cleanup_queue() calls.
Wouldn't concurrent blk_cleanup_queue() calls be a bug? If so should
I make it clear that it would be or simply prevent it?
> Callers of
> blk_get_queue() may encounter a change of the queue state from normal
> into dying any time during the blk_get_queue() call or after
> blk_get_queue() has finished. Maybe I'm overlooking something but I
> doubt that modifying blk_get_queue() will help.
Good point, to fix that race described by Christoph we'd have to take
into consideration refcounts of the request_queue to prevent queues from
changing state to dying if the refcount is > 1, however that'd also
would mean not allowing the request_queue from ever dying.
One way we could resolve this could be to to keep track of a
quiesce/dying request, then at that point prevent blk_get_queue() from
allowing increments, and once the refcount is down to 1, flip the switch
to dying.
Luis
next prev parent reply other threads:[~2020-04-16 1:12 UTC|newest]
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
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 [this message]
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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