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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 18 Apr 2011 13:27:10 -0700
Message-ID: <BANLkTi=Oo03CQchHYh4EvEsk+wZy7akLNw@mail.gmail.com>
Subject: Re: 2.6.39-rc1 nouveau(?) regression (bisected)
To: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Kyle Spaans <kspaans@uwaterloo.ca>, linux-kernel@vger.kernel.org,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Ben Skeggs <bskeggs@redhat.com>, airlied@redhat.com,
        dri-devel@lists.freedesktop.org, mjg@redhat.com,
        maciej.rutecki@gmail.com, nouveau@lists.freedesktop.org,
        Nigel Cunningham <lkml@nigelcunningham.com.au>,
        Nick Piggin <npiggin@gmail.com>
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On Mon, Apr 18, 2011 at 1:02 PM, Marcin Slusarz
<marcin.slusarz@gmail.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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