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 [thread overview]
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
next prev parent reply other threads:[~2020-04-15 12:36 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 [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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