From: Jens Axboe <jaxboe@fusionio.com>
To: Paul Bolle <pebolle@tiscali.nl>
Cc: "paulmck@linux.vnet.ibm.com" <paulmck@linux.vnet.ibm.com>,
Vivek Goyal <vgoyal@redhat.com>,
linux kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: Mysterious CFQ crash and RCU
Date: Mon, 6 Jun 2011 00:51:10 +0200 [thread overview]
Message-ID: <4DEC085E.3080506@fusionio.com> (raw)
In-Reply-To: <1307270324.25014.14.camel@t41.thuisdomein>
On 2011-06-05 12:38, Paul Bolle wrote:
> On Sun, 2011-06-05 at 10:39 +0200, Paul Bolle wrote:
>> 0) I'd guess not, as the last thing I tried before simply ripping
>> io_context.ioc_data out, was:
>>
>> spin_lock_irqsave(&ioc->lock, flags);
>> rcu_read_lock();
>> ioc_data = rcu_dereference(ioc->ioc_data);
>> rcu_read_unlock();
>> if (ioc_data == cic)
>> rcu_assign_pointer(ioc->ioc_data, NULL);
>> spin_unlock_irqrestore(&ioc->lock, flags);
You don't need to nest a rcu_read_lock/unlock() inside that write lock.
> 0) Strike that. It does seem to fix it. I must have done something silly
> while doing yet another test of this stuff (perhaps by forgetting to
> remove an old, crashing version of the cfq_iosched module before
> installing a new version and switching back to cfq).
Good, I thought it should!
> 1) Jens, I suggest I'll send in a small series of patches, along these
> lines:
> - cleanup: make two functions static in block/cfq-iosched.c
> - cleanup: rename io_context.cic_list -> io_context.cic_hlist
> rename io_context.ioc_data -> io_context.last_cic
> change io_context.last_cic from void* to cfq_io_context*
> rename cfq_io_context.cic_list -> cfq_io_context.cic_node
> - cleanup: rename *ret -> *ioc in two functions
> - locking: make sure io_context.last_cic is accessed under
> io_context.lock and using the required RCU voodoo
>
> 2) Any objections beforehand?
I've already applied the fix I sent to you, since it was definitely a
bug. So please send anything around that. Was out today, so not pushed
out until now and just now catching up on the email.
And thanks a ton for being persistent and doing a ton of work trying to
figure out what was wrong. Fixing is the easy part, illuminating where
the problem is or may be is the hard part!
--
Jens Axboe
next prev parent reply other threads:[~2011-06-05 22:51 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-19 22:24 Mysterious CFQ crash and RCU Vivek Goyal
2011-05-21 21:00 ` Paul E. McKenney
2011-05-21 22:23 ` Paul Bolle
2011-05-21 23:54 ` Paul E. McKenney
2011-05-22 19:30 ` Paul Bolle
2011-05-22 20:13 ` Paul E. McKenney
2011-05-23 15:21 ` Vivek Goyal
2011-05-23 15:38 ` Paul E. McKenney
2011-05-23 22:20 ` Paul Bolle
2011-05-24 4:14 ` Paul E. McKenney
2011-05-24 9:41 ` Jens Axboe
2011-05-24 14:35 ` Paul E. McKenney
2011-05-24 14:51 ` Jens Axboe
2011-05-24 15:42 ` Paul E. McKenney
2011-05-24 15:51 ` Paul E. McKenney
2011-05-25 8:28 ` Paul Bolle
2011-05-25 8:46 ` Jens Axboe
2011-05-25 9:13 ` Paul Bolle
2011-05-25 9:30 ` Jens Axboe
2011-05-25 9:40 ` Paul Bolle
2011-05-25 12:48 ` Paul Bolle
2011-05-25 12:51 ` Jens Axboe
2011-05-25 17:28 ` Paul Bolle
2011-05-25 18:59 ` Jens Axboe
2011-05-25 10:17 ` Paul Bolle
2011-05-25 15:33 ` Paul E. McKenney
2011-05-25 17:44 ` Paul Bolle
2011-05-25 20:40 ` Paul E. McKenney
2011-05-26 9:15 ` Paul Bolle
2011-06-03 5:07 ` Paul E. McKenney
2011-06-03 13:45 ` Vivek Goyal
2011-06-03 15:33 ` Paul E. McKenney
2011-06-03 16:54 ` Paul E. McKenney
2011-06-04 12:22 ` Paul Bolle
2011-06-04 12:50 ` Paul Bolle
2011-06-04 16:03 ` Paul E. McKenney
2011-06-04 22:48 ` Paul Bolle
2011-06-04 23:06 ` Paul E. McKenney
2011-08-04 15:05 ` Vivek Goyal
2011-08-04 19:43 ` Jens Axboe
2011-08-04 19:51 ` Vivek Goyal
2011-06-05 6:56 ` Jens Axboe
2011-06-05 8:39 ` Paul Bolle
2011-06-05 10:38 ` Paul Bolle
2011-06-05 22:51 ` Jens Axboe [this message]
2011-06-06 14:28 ` Vivek Goyal
2011-05-23 15:36 ` Vivek Goyal
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