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SubjectRe: .17rc5 cfq slab corruption.
On Tue, May 30 2006, Dave Jones wrote:
> On Tue, May 30, 2006 at 03:17:28PM +0200, Jens Axboe wrote:
> > On Sat, May 27 2006, Dave Jones wrote:
> > > On Sat, May 27, 2006 at 09:07:24AM +0200, Jens Axboe wrote:
> > > > On Fri, May 26 2006, Andrew Morton wrote:
> > > > > Dave Jones <davej@redhat.com> wrote:
> > > > > >
> > > > > > Was playing with googles new picasa toy, which hammered the disks
> > > > > > hunting out every image file it could find, when this popped out:
> > > > > >
> > > > > > Slab corruption: (Not tainted) start=ffff810012b998c8, len=168
> > > > > > Redzone: 0x5a2cf071/0x5a2cf071.
> > > > > > Last user: [<ffffffff8032c319>](cfq_free_io_context+0x2f/0x74)
> > > > > > 090: 10 bd 28 1b 00 81 ff ff 6b 6b 6b 6b 6b 6b 6b 6b
> > > > > > Prev obj: start=ffff810012b99808, len=168
> > > > > > Redzone: 0x5a2cf071/0x5a2cf071.
> > > > > > Last user: [<ffffffff8032c319>](cfq_free_io_context+0x2f/0x74)
> > > > > > 000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> > > > > > 010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> > > > > > Next obj: start=ffff810012b99988, len=168
> > > > > > Redzone: 0x5a2cf071/0x5a2cf071.
> > > > > > Last user: [<ffffffff8032c319>](cfq_free_io_context+0x2f/0x74)
> > > > > > 000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> > > > > > 010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> > > >
> > > > Pretty baffling... cfq has been hammered pretty thoroughly over the
> > > > last months and _nothing_ has shown up except some performance anomalies
> > > > that are now fixed. Since daves case (at least) seems to be
> > > > use-after-free, I'll see if I can reproduce with some contrived case.
> > > > I'm asuming that picasa forks and exits a lot with submitted io in
> > > > between than may not have finished at exit.
> > >
> > > The second time I hit it, was actually during boot up.
> >
> > Dave, do you have any io scheduler switching going on?
>
> Here's something interesting (possibly unrelated).
> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=193534
>
> I added this patch to our devel kernel (based on 17rc5-git5 right now)
>
> It's similar to the list_head debugging patch from -mm
>
> --- linux-2.6.12/include/linux/list.h~ 2005-08-08 15:34:50.000000000 -0400
> +++ linux-2.6.12/include/linux/list.h 2005-08-08 15:35:22.000000000 -0400
> @@ -5,7 +5,9 @@
>
> #include <linux/stddef.h>
> #include <linux/prefetch.h>
> +#include <linux/kernel.h>
> #include <asm/system.h>
> +#include <asm/bug.h>
>
> /*
> * These are non-NULL pointers that will result in page faults
> @@ -52,6 +52,16 @@ static inline void __list_add(struct lis
> struct list_head *prev,
> struct list_head *next)
> {
> + if (next->prev != prev) {
> + printk("List corruption. next->prev should be %p, but was %p\n",
> + prev, next->prev);
> + BUG();
> + }
> + if (prev->next != next) {
> + printk("List corruption. prev->next should be %p, but was %p\n",
> + next, prev->next);
> + BUG();
> + }
> next->prev = new;
> new->next = next;
> new->prev = prev;
> @@ -162,6 +162,16 @@ static inline void __list_del(struct lis
> */
> static inline void list_del(struct list_head *entry)
> {
> + if (entry->prev->next != entry) {
> + printk("List corruption. prev->next should be %p, but was %p\n",
> + entry, entry->prev->next);
> + BUG();
> + }
> + if (entry->next->prev != entry) {
> + printk("List corruption. next->prev should be %p, but was %p\n",
> + entry, entry->next->prev);
> + BUG();
> + }
> __list_del(entry->prev, entry->next);
> entry->next = LIST_POISON1;
> entry->prev = LIST_POISON2;
>
>
> And then it turned up this:
>
> List corruption. next->prev should be f74a5e2c, but was ea7ed31c
> Pointing at cfq_set_request.

I think I'm missing a piece of this - what list was corrupted, in what
function did it trigger?


--
Jens Axboe

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