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From: Luis Chamberlain <mcgrof@kernel.org>
To: Nicolai Stange <nstange@suse.de>
Cc: Bart Van Assche <bvanassche@acm.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,
	mhocko@suse.com, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Omar Sandoval <osandov@fb.com>, Hannes Reinecke <hare@suse.com>,
	Michal Hocko <mhocko@kernel.org>
Subject: Re: [RFC 3/3] block: avoid deferral of blk_release_queue() work
Date: Thu, 9 Apr 2020 18:11:11 +0000	[thread overview]
Message-ID: <20200409181111.GJ11244@42.do-not-panic.com> (raw)
In-Reply-To: <87o8saj62m.fsf@suse.de>

On Thu, Apr 02, 2020 at 04:49:37PM +0200, Nicolai Stange wrote:
> Bart Van Assche <bvanassche@acm.org> writes:
> 
> > On 2020-04-01 17:00, Luis Chamberlain wrote:
> > The description of this patch mentions a single blk_release_queue() call
> > that happened in the past from a context from which sleeping is not
> > allowed and from which sleeping is allowed today. Have all other
> > blk_release_queue() / blk_put_queue() calls been verified to see whether
> > none of these happens from a context from which sleeping is not allowed?
> 
> I've just done this today and found the following potentially
> problematic call paths to blk_put_queue().
> 
> 1.) mem_cgroup_throttle_swaprate() takes a spinlock and
>     calls blkcg_schedule_throttle()->blk_put_queue().
> 
>     Also note that AFAICS mem_cgroup_try_charge_delay() can be called
>     with GFP_ATOMIC.

I have a solution to this which would avoid having to deal with the
concern completely. I'll post in my follow up.

> 2.) scsi_unblock_requests() gets called from a lot of drivers and
>     invoke blk_put_queue() through
>     scsi_unblock_requests() -> scsi_run_host_queues() ->
>     scsi_starved_list_run() -> blk_put_queue().

sd_probe() calls device_add_disk(), and the scsi lib also has its
own refcounting for scsi, but unless you call sd_remove() you'll be
protecting the underlying block disk and request_queue, as sd_remove()
calls the del_gendisk() which would in call call blk_unregister_queue()
which calls the last blk_put_queue(). If sd_remove() can be called from
atomic context we can also fix this, and this should be evident how in
my next follow up series of patches.

  Luis

  parent reply	other threads:[~2020-04-09 18:11 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-01 23:59 [RFC 0/3] block: address blktrace use-after-free Luis Chamberlain
2020-04-02  0:00 ` [RFC 1/3] block: move main block debugfs initialization to its own file Luis Chamberlain
2020-04-05  3:12   ` Bart Van Assche
2020-04-06 14:23     ` Luis Chamberlain
2020-04-02  0:00 ` [RFC 2/3] blktrace: fix debugfs use after free Luis Chamberlain
2020-04-02  1:57   ` Eric Sandeen
2020-04-02 16:14     ` Luis Chamberlain
2020-04-05  3:39   ` Bart Van Assche
2020-04-06  1:27     ` Eric Sandeen
2020-04-06  4:25       ` Bart Van Assche
2020-04-06  9:18         ` Nicolai Stange
2020-04-06 15:19           ` Luis Chamberlain
2020-04-07  8:15             ` Luis Chamberlain
2020-04-06 14:29         ` Eric Sandeen
2020-04-07  8:09           ` Luis Chamberlain
2020-04-06 15:14     ` Luis Chamberlain
2020-04-02  0:00 ` [RFC 3/3] block: avoid deferral of blk_release_queue() work Luis Chamberlain
2020-04-02  3:39   ` Bart Van Assche
2020-04-02 14:49     ` Nicolai Stange
2020-04-06  9:11       ` Nicolai Stange
2020-04-09 18:11       ` Luis Chamberlain [this message]
2020-04-02  7:44 ` [RFC 0/3] block: address blktrace use-after-free Greg KH
2020-04-03  8:19 ` Ming Lei
2020-04-03 14:06   ` Luis Chamberlain
2020-04-03 14:13   ` Bart Van Assche
2020-04-03 19:49     ` Luis Chamberlain
2020-04-07  2:47   ` yukuai (C)
2020-04-07 19:00     ` Luis Chamberlain
2020-04-09 20:59       ` Luis Chamberlain

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