From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "tj@kernel.org" <tj@kernel.org>,
"00moses.alexander00@gmail.com" <00moses.alexander00@gmail.com>,
"joseph.qi@linux.alibaba.com" <joseph.qi@linux.alibaba.com>
Cc: "nborisov@suse.com" <nborisov@suse.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"arnd@arndb.de" <arnd@arndb.de>,
"axboe@kernel.dk" <axboe@kernel.dk>, "shli@fb.com" <shli@fb.com>
Subject: Re: [PATCH v2] blk-cgroup: remove entries in blkg_tree before queue release
Date: Wed, 11 Apr 2018 16:42:55 +0000 [thread overview]
Message-ID: <bd60302129cb89bdc3b4f402ce4e061f41851729.camel@wdc.com> (raw)
In-Reply-To: <20180411145632.GK793541@devbig577.frc2.facebook.com>
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WARNING: multiple messages have this Message-ID (diff)
From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "tj@kernel.org" <tj@kernel.org>,
"00moses.alexander00@gmail.com" <00moses.alexander00@gmail.com>,
"joseph.qi@linux.alibaba.com" <joseph.qi@linux.alibaba.com>
Cc: "nborisov@suse.com" <nborisov@suse.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"arnd@arndb.de" <arnd@arndb.de>,
"axboe@kernel.dk" <axboe@kernel.dk>, "shli@fb.com" <shli@fb.com>
Subject: Re: [PATCH v2] blk-cgroup: remove entries in blkg_tree before queue release
Date: Wed, 11 Apr 2018 16:42:55 +0000 [thread overview]
Message-ID: <bd60302129cb89bdc3b4f402ce4e061f41851729.camel@wdc.com> (raw)
In-Reply-To: <20180411145632.GK793541@devbig577.frc2.facebook.com>
On Wed, 2018-04-11 at 07:56 -0700, Tejun Heo wrote:
> And looking at the change, it looks like the right thing we should
> have done is caching @lock on the print_blkg side and when switching
> locks make sure both locks are held. IOW, do the following in
> blk_cleanup_queue()
>
> spin_lock_irq(lock);
> if (q->queue_lock != &q->__queue_lock) {
> spin_lock(&q->__queue_lock);
> q->queue_lock = &q->__queue_lock;
> spin_unlock(&q->__queue_lock);
> }
> spin_unlock_irq(lock);
>
> Otherwise, there can be two lock holders thinking they have exclusive
> access to the request_queue.
I think that's a bad idea. A block driver is allowed to destroy the
spinlock it associated with the request queue as soon as blk_cleanup_queue()
has finished. If the block cgroup controller would cache a pointer to the
block driver spinlock then that could cause the cgroup code to attempt to
lock a spinlock after it has been destroyed. I don't think we need that kind
of race conditions.
Bart.
next prev parent reply other threads:[~2018-04-11 16:42 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-07 10:21 [PATCH v2] blk-cgroup: remove entries in blkg_tree before queue release Alexandru Moise
2018-04-09 22:09 ` Tejun Heo
2018-04-11 10:12 ` Alexandru Moise
2018-04-11 14:20 ` Tejun Heo
2018-04-11 14:28 ` Alexandru Moise
2018-04-11 14:46 ` Tejun Heo
2018-04-11 14:51 ` Tejun Heo
2018-04-11 14:56 ` Tejun Heo
2018-04-11 16:42 ` Bart Van Assche [this message]
2018-04-11 16:42 ` Bart Van Assche
2018-04-11 17:00 ` tj
2018-04-11 17:06 ` Bart Van Assche
2018-04-11 17:06 ` Bart Van Assche
2018-04-11 17:15 ` tj
2018-04-11 17:26 ` Bart Van Assche
2018-04-11 17:26 ` Bart Van Assche
2018-04-11 17:30 ` tj
2018-04-11 15:54 ` Bart Van Assche
2018-04-11 15:54 ` Bart Van Assche
2018-04-11 19:00 ` Alexandru Moise
2018-04-11 19:55 ` Bart Van Assche
2018-04-11 19:57 ` tj
2018-04-11 20:00 ` Bart Van Assche
2018-04-11 20:00 ` Bart Van Assche
2018-04-11 20:02 ` tj
2018-04-11 20:23 ` Bart Van Assche
2018-04-11 20:23 ` Bart Van Assche
2018-04-11 21:23 ` Alexandru Moise
2018-04-11 21:28 ` Bart Van Assche
2018-04-11 21:28 ` Bart Van Assche
2018-04-11 22:58 ` Alexandru Moise
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