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Date: Tue, 20 Sep 2011 16:32:52 +0900
From: "Jun'ichi Nomura" <j-nomura@...jp.nec.com>
To: Ben Hutchings <ben@...adent.org.uk>, jaxboe@...ionio.com
CC: Alan Stern <stern@...land.harvard.edu>,
James Bottomley <James.Bottomley@...senPartnership.com>,
Rocko Requin <rockorequin@...mail.com>, tytso@....edu,
Kernel development list <linux-kernel@...r.kernel.org>,
linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [Bug 25832] kernel crashes when a mounted ext3/4 file system
is physically removed
On 09/19/11 08:00, Ben Hutchings wrote:
> On Sat, 2011-09-17 at 13:34 -0400, Alan Stern wrote:
>> On Sat, 17 Sep 2011, Rocko Requin wrote:
>>
>>>> Why were you using gnome-terminal? You should be running the tests at
>>>> a console VT, not under X at all. Ctrl-Alt-F2 or the equivalent...
>>>
>>> Because with Ted's patch it doesn't crash when run from a console VT, even with an X server running.
>>
>> That's weird. Maybe the screen updates change some timing.
>>
>>>> Here's another patch to address the new problem. You can apply it on
>>>> top of all the other patches.
>>>
>>> Attached is the crash log I get with the latest patch applied.
>>
>> Okay, more fallout from the same problem. Here's an updated version of
>> the previous patch.
> [...]
>
> There have been reports of this in Debian going back to 2.6.39:
>
> http://bugs.debian.org/631187
> http://bugs.debian.org/636263
> http://bugs.debian.org/642043
>
> Plus possibly related crashes in elv_put_request after CD-ROM removal:
>
> http://bugs.debian.org/633890
> http://bugs.debian.org/634681
> http://bugs.debian.org/636103
>
> The former was also reported in Ubuntu since their 2.6.38-10:
>
> https://bugs.launchpad.net/debian/+source/linux-2.6/+bug/793796
>
> The result of the discussion there was that it appeared to be a
> regression due to commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b
> ("[SCSI] put stricter guards on queue dead checks") which was also
> included in a stable update for 2.6.38.
>
> There was also a report on bugzilla.kernel.org, though no-one can see
> quite what that says now:
>
> https://bugzilla.kernel.org/show_bug.cgi?id=38842
>
> I also reported most of the above to James Bottomley and linux-scsi
> nearly 2 months ago, to no response.
I've reported a similar oops related to the above commit:
[BUG] Oops when SCSI device under multipath is removed
https://lkml.org/lkml/2011/8/10/11
Elevator being removed is the core of the problem.
And the essential issue seems 2 different models of queue/driver relation
implied by queue_lock.
If reverting the commit is not an option,
until somebody comes up to fix the essential issue,
the patch below should close the regressions introduced by the commit.
Thanks,
--
Jun'ichi Nomura, NEC Corporation
This patch moves elevator_exit() and blk_throtl_exit() from
blk_cleanup_queue() to blk_release_queue() when it is possible.
elevator_exit() and blk_throtl_exit() were called in blk_cleanup_queue()
because they use queue_lock.
There are 2 types of queue_locks:
a) supplied by driver (via blk_init_queue)
b) embedded in struct request_queue (__queue_lock)
When queue_lock is supplied by driver, there is no guarantee that
the pointer is valid after blk_cleanup_queue(), so they have to be
called in blk_cleanup_queue().
In this case, the driver has to make sure nobody is using the queue
before calling blk_cleanup_queue().
However, OTOH, if queue_lock is '__queue_lock' in request_queue,
blk_release_queue() is better place for freeing structures
because the block layer knows for sure there is no reference.
This patch is ugly but should fix various oopses introduced by this change:
86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b
[SCSI] put stricter guards on queue dead checks
For example:
https://lkml.org/lkml/2011/8/10/11
Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
Index: linux-3.1-rc4/block/blk-core.c
===================================================================
--- linux-3.1-rc4.orig/block/blk-core.c 2011-08-29 13:16:01.000000000 +0900
+++ linux-3.1-rc4/block/blk-core.c 2011-09-20 15:53:23.496814819 +0900
@@ -352,6 +352,14 @@
* unexpectedly as some queue cleanup components like elevator_exit() and
* blk_throtl_exit() need queue lock.
*/
+void blk_release_queue_components_with_queuelock(struct request_queue *q)
+{
+ if (q->elevator)
+ elevator_exit(q->elevator);
+
+ blk_throtl_exit(q);
+}
+
void blk_cleanup_queue(struct request_queue *q)
{
/*
@@ -367,10 +375,12 @@
queue_flag_set_unlocked(QUEUE_FLAG_DEAD, q);
mutex_unlock(&q->sysfs_lock);
- if (q->elevator)
- elevator_exit(q->elevator);
-
- blk_throtl_exit(q);
+ /*
+ * A driver supplied the queue lock.
+ * Cleanup components while the queue lock is valid.
+ */
+ if (q->queue_lock != &q->__queue_lock)
+ blk_release_queue_components_with_queuelock(q);
blk_put_queue(q);
}
Index: linux-3.1-rc4/block/blk-sysfs.c
===================================================================
--- linux-3.1-rc4.orig/block/blk-sysfs.c 2011-09-19 09:38:51.000000000 +0900
+++ linux-3.1-rc4/block/blk-sysfs.c 2011-09-20 15:57:50.358807023 +0900
@@ -477,6 +477,9 @@
blk_sync_queue(q);
+ if (q->queue_lock == &q->__queue_lock)
+ blk_release_queue_components_with_queuelock(q);
+
if (rl->rq_pool)
mempool_destroy(rl->rq_pool);
Index: linux-3.1-rc4/block/blk.h
===================================================================
--- linux-3.1-rc4.orig/block/blk.h 2011-08-29 13:16:01.000000000 +0900
+++ linux-3.1-rc4/block/blk.h 2011-09-20 15:57:38.306807136 +0900
@@ -25,6 +25,9 @@
void blk_add_timer(struct request *);
void __generic_unplug_device(struct request_queue *);
+/* Wrapper to release functions to be called while queue_lock is valid */
+void blk_release_queue_components_with_queuelock(struct request_queue *q);
+
/*
* Internal atomic flags for request handling
*/
--
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