linux-kernel - Re: 2.6.39-rc1 nouveau(?) regression (bisected)

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Date:	Mon, 18 Apr 2011 13:27:10 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
Cc:	Kyle Spaans <kspaans@...terloo.ca>, linux-kernel@...r.kernel.org,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Ben Skeggs <bskeggs@...hat.com>, airlied@...hat.com,
	dri-devel@...ts.freedesktop.org, mjg@...hat.com,
	maciej.rutecki@...il.com, nouveau@...ts.freedesktop.org,
	Nigel Cunningham <lkml@...elcunningham.com.au>,
	Nick Piggin <npiggin@...il.com>
Subject: Re: 2.6.39-rc1 nouveau(?) regression (bisected)

On Mon, Apr 18, 2011 at 1:02 PM, Marcin Slusarz
<marcin.slusarz@...il.com> wrote:
>
> It's some nasty corruption:

Looks like something wrote 0xffffffff to free'd memory.

Enabling DEBUG_PAGEALLOC *might* show where it happens.

>
> [    6.523867] =============================================================================
> [    6.523916] BUG sysfs_dir_cache: Poison overwritten
> [    6.523949] -----------------------------------------------------------------------------
> [    6.523950]
> [    6.524016] INFO: 0xffff8801bb47df4c-0xffff8801bb47df4f. First byte 0xff instead of 0x6b
> [    6.524061] INFO: Slab 0xffffea00060f7b58 objects=22 used=21 fp=0xffff8801bb47df18 flags=0x80000000000000c1
> [    6.524110] INFO: Object 0xffff8801bb47df18 @offset=3864 fp=0x          (null)
> [    6.524111]
> [    6.524170] Bytes b4 0xffff8801bb47df08:  00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
> [    6.524516]   Object 0xffff8801bb47df18:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> [    6.524862]   Object 0xffff8801bb47df28:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> [    6.525208]   Object 0xffff8801bb47df38:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> [    6.525556]   Object 0xffff8801bb47df48:  6b 6b 6b 6b ff ff ff ff 6b 6b 6b 6b 6b 6b 6b 6b kkkk<FF><FF><FF><FF>kkkkkkkk

So here the 0xffffffff is pretty obvious.

> and in another boot:
>
> [    6.704786] BUG: unable to handle kernel paging request at ffffffffbc70b058

Here it is less obvious, but it was _probably_ a regular kernel
pointer of the type 0xffff8801bc70b058 before the high bits were
overwritten by a 0xffffffff.

So then sysfs_refresh_inode() follows that pointer, and crashes.

Just a guess, obviously, but it looks rather likely.

                         Linus
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