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SubjectRe: [bug, 2.6.26-rc4/rc5] sporadic bootup crashes in blk_lookup_devt()/prepare_namespace()
On 6/9/08, Cornelia Huck <cornelia.huck@de.ibm.com> wrote:
> On Mon, 9 Jun 2008 16:28:09 +0200,
>
> "Vegard Nossum" <vegard.nossum@gmail.com> wrote:
> > Everywhere else where we traverse the struct class->devices list, they
> > have down(&class->sem); first and up(&class->sem); afterwards.
> >
> > Commit fd04897bb20be29d60f7e426a053545aebeaa61a even has this hunk:
> > @@ -177,8 +177,7 @@ struct class {
> > struct list_head devices;
> > struct list_head interfaces;
> > struct kset class_dirs;
> > - struct semaphore sem; /* locks both the children and interface
> > -
> > + struct semaphore sem; /* locks children, devices, interfaces */
> > struct class_attribute * class_attrs;
> > struct class_device_attribute * class_dev_attrs;
> > struct device_attribute * dev_attrs;
> >
> >
> > So why doesn't block/genhd.c do this too? It seems to me that the
> > mutex locking here is simply a remnant of old code that happened to
> > not crash in most cases by chance.
> >
>
>
> Does this crash happen with the conversion to the class iterator
> functions (should be in linux-next) as well? They take the class
> mutex...

Ah, you mean this:

commit bb7ee70edb8745021c17ab604f2f4c897004e1c5
Author: Greg Kroah-Hartman <gregkh@suse.de>
Date: Thu May 22 17:21:08 2008 -0400

block: make blk_lookup_devt use the class iterator function

Use the proper class iterator function instead of mucking around in the
internals of the class structures.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

So it should already be fixed, then. But I guess we'll have to wait
for Ingo to run another couple of thousand tests to know the answer
;-)

Thanks!

Hm. Bugs already fixed elsewhere seems to be a recurring theme... I'll
look harder for changes/fixes in other trees the next time :-(


Vegard

PS: But what about printk_all_partitions()? There are more than just
this instance of the device list traversal code that don't use the
class semaphore.

PPS: Was that patch ever posted to LKML? I couldn't seem to find it.

--
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
-- E. W. Dijkstra, EWD1036


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