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 N�rnberg
GF: F. Imend�rffer, J. Smithard, D. Upmanyu, G. Norton
HRB 21284 (AG N�rnberg)
WARNING: multiple messages have this Message-ID (diff)
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: 36+ 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 0:31 ` Bart Van Assche
2017-01-31 16:15 ` Hannes Reinecke [this message]
2017-01-31 16:15 ` Hannes Reinecke
2017-02-03 12:22 ` Dexuan Cui
2017-02-03 12:22 ` Dexuan Cui
2017-02-07 2:23 ` Dexuan Cui
2017-02-07 2:23 ` Dexuan Cui
2017-02-07 2:56 ` Bart Van Assche
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 6:29 ` Dexuan Cui
2017-02-07 16:09 ` Jens Axboe
2017-02-08 10:48 ` Dexuan Cui
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 7:35 ` Dexuan Cui
2017-02-09 13:08 ` hch
2017-02-10 14:49 ` Dexuan Cui
2017-02-10 14:49 ` Dexuan Cui
2017-02-14 13:47 ` hch
2017-02-14 14:17 ` Dexuan Cui
2017-02-14 14:17 ` Dexuan Cui
2017-02-14 14:28 ` hch
2017-02-14 14:46 ` Dexuan Cui
2017-02-14 14:46 ` Dexuan Cui
2017-02-14 14:51 ` hch
2017-02-14 15:54 ` Dexuan Cui
2017-02-14 15:54 ` Dexuan Cui
2017-02-14 16:34 ` hch
2017-02-15 13:51 ` Dexuan Cui
2017-02-15 13:51 ` Dexuan Cui
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=532c55c4-15da-d2f9-401c-36bc4343756b@suse.com \
--to=hare@suse.com \
--cc=Bart.VanAssche@sandisk.com \
--cc=axboe@kernel.dk \
--cc=hare@suse.de \
--cc=hch@lst.de \
--cc=jth@kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.