From: Hannes Reinecke <hare@suse.com>
To: Bart Van Assche <Bart.VanAssche@sandisk.com>,
"hare@suse.de" <hare@suse.de>,
"axboe@kernel.dk" <axboe@kernel.dk>
Cc: "hch@lst.de" <hch@lst.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"jth@kernel.org" <jth@kernel.org>
Subject: Re: [PATCH] genhd: Do not hold event lock when scheduling workqueue elements
Date: Tue, 31 Jan 2017 17:15:06 +0100 [thread overview]
Message-ID: <532c55c4-15da-d2f9-401c-36bc4343756b@suse.com> (raw)
In-Reply-To: <1485822639.2669.16.camel@sandisk.com>
On 01/31/2017 01:31 AM, Bart Van Assche wrote:
> On Wed, 2017-01-18 at 10:48 +0100, Hannes Reinecke wrote:
>> @@ -1488,26 +1487,13 @@ static unsigned long disk_events_poll_jiffies(struct gendisk *disk)
>> void disk_block_events(struct gendisk *disk)
>> {
>> struct disk_events *ev = disk->ev;
>> - unsigned long flags;
>> - bool cancel;
>>
>> if (!ev)
>> return;
>>
>> - /*
>> - * Outer mutex ensures that the first blocker completes canceling
>> - * the event work before further blockers are allowed to finish.
>> - */
>> - mutex_lock(&ev->block_mutex);
>> -
>> - spin_lock_irqsave(&ev->lock, flags);
>> - cancel = !ev->block++;
>> - spin_unlock_irqrestore(&ev->lock, flags);
>> -
>> - if (cancel)
>> + if (atomic_inc_return(&ev->block) == 1)
>> cancel_delayed_work_sync(&disk->ev->dwork);
>>
>> - mutex_unlock(&ev->block_mutex);
>> }
>
> Hello Hannes,
>
> I have already encountered a few times a deadlock that was caused by the
> event checking code so I agree with you that it would be a big step forward
> if such deadlocks wouldn't occur anymore. However, this patch realizes a
> change that has not been described in the patch description, namely that
> disk_block_events() calls are no longer serialized. Are you sure it is safe
> to drop the serialization of disk_block_events() calls?
>
Well, this whole synchronization stuff it a bit weird; I so totally fail
to see the rationale for it.
But anyway, once we've converted ev->block to atomics I _think_ the
mutex_lock can remain; will be checking.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.com +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
next prev parent reply other threads:[~2017-01-31 16:15 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-18 9:48 [PATCH] genhd: Do not hold event lock when scheduling workqueue elements Hannes Reinecke
2017-01-31 0:31 ` Bart Van Assche
2017-01-31 16:15 ` Hannes Reinecke [this message]
2017-02-03 12:22 ` Dexuan Cui
2017-02-07 2:23 ` Dexuan Cui
2017-02-07 2:56 ` Bart Van Assche
2017-02-07 3:48 ` Dexuan Cui
2017-02-07 6:29 ` Dexuan Cui
2017-02-07 16:09 ` Jens Axboe
2017-02-08 10:48 ` Dexuan Cui
2017-02-08 17:43 ` Boot regression (was "Re: [PATCH] genhd: Do not hold event lock when scheduling workqueue elements") Jens Axboe
2017-02-08 18:03 ` hch
2017-02-09 7:35 ` Dexuan Cui
2017-02-09 13:08 ` hch
2017-02-10 14:49 ` Dexuan Cui
2017-02-14 13:47 ` hch
2017-02-14 14:17 ` Dexuan Cui
2017-02-14 14:28 ` hch
2017-02-14 14:46 ` Dexuan Cui
2017-02-14 14:51 ` hch
2017-02-14 15:54 ` Dexuan Cui
2017-02-14 16:34 ` hch
2017-02-15 13:51 ` Dexuan Cui
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