linux-kernel - Re: general protection fault: 0000 [#1] SMP

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Date:	Mon, 22 Nov 2010 12:25:25 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	"Justin P. Mattock" <justinmattock@...il.com>
cc:	Jesper Juhl <jj@...osbits.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: general protection fault: 0000 [#1] SMP

On Mon, 22 Nov 2010, Justin P. Mattock wrote:

> <---- cut -------->
> 
> cleaned the thread up.. Anyways after doing some debugging with gdb and with
> valgrind for an application that keeps segfaulting I noticed this in dmesg:
> 
> [ 3028.571941] FIREWALL:INPUT IN=wlan0 OUT=
> MAC=ff:ff:ff:ff:ff:ff:00:23:12:65:cb:02:08:00 SRC=0.0.0.0
> DST=255.255.255.255 LEN=328 TOS=0x00 PREC=0x00 TTL=255 ID=57984 PROTO=UDP
> SPT=68 DPT=67 LEN=308
> [ 3061.177655] BUG: Bad page state in process make  pfn:2134c
> [ 3061.177661] page:ffffea00007438a0 count:0 mapcount:0 mapping:   (null)
> index:0x507
> [ 3061.177663] page flags: 0x4000000000000008(uptodate)
> [ 3061.177669] Pid: 5691, comm: make Not tainted 2.6.37-rc2-00039-g0211924
> #7
> [ 3061.177671] Call Trace:
> [ 3061.177680]  [<ffffffff810c5900>] ? dump_page+0xc0/0xc5
> [ 3061.177684]  [<ffffffff810c5f18>] bad_page+0xd8/0xea
> [ 3061.177688]  [<ffffffff810c7aeb>] get_page_from_freelist+0x344/0x4a0
> [ 3061.177693]  [<ffffffff811bf123>] ? inode_has_perm+0x68/0x6a
> [ 3061.177697]  [<ffffffff810c7d6b>] __alloc_pages_nodemask+0x124/0x645
> [ 3061.177701]  [<ffffffff810f7cf2>] ? __dentry_open+0x194/0x2a1
> [ 3061.177705]  [<ffffffff810dc155>] handle_mm_fault+0x2a8/0x82f
> [ 3061.177710]  [<ffffffff811056ec>] ? do_filp_open+0x1f3/0x646
> [ 3061.177714]  [<ffffffff810f4226>] ? check_object+0x13b/0x1eb
> [ 3061.177719]  [<ffffffff81447d8e>] do_page_fault+0x3ec/0x411
> [ 3061.177722]  [<ffffffff810f4b95>] ? free_debug_processing+0x1c5/0x208
> [ 3061.177726]  [<ffffffff81103958>] ? getname+0x2c/0x1be
> [ 3061.177728]  [<ffffffff810f4d08>] ? __slab_free+0x130/0x145
> [ 3061.177732]  [<ffffffff81444e25>] page_fault+0x25/0x30
> [ 3061.177734] Disabling lock debugging due to kernel taint
> [ 3126.418774] type=1400 audit(1290451825.417:178): avc:  denied
> 
> from what I remember using valgirnd with the app took a while to load but am
> unsure if is the reason for the above message.

This particular error is almost certainly fixed by rc3's patch below.
Whether your earlier errors are a side-effect of the same Uptodate bug
I cannot say: it's conceivable, but I don't see it as likely.  Maybe
you should just move up to rc3 and see what happens with that.

Hugh

From: Markus Trippelsdorf <markus@...ppelsdorf.de>
Date: Thu, 18 Nov 2010 02:46:06 +0000 (-0500)
Subject: ext4: fix setting random pages PageUptodate
X-Git-Tag: v2.6.37-rc3~1^2~5
X-Git-Url: http://127.0.0.1:1234/?p=.git;a=commitdiff_plain;h=08da1193d2c8c7a25d0cef7f85d0b9f1ad7c583a

ext4: fix setting random pages PageUptodate

ext4_end_bio calls put_page and kmem_cache_free before calling
SetPageUpdate(). This can result in setting the PageUptodate bit on
random pages and causes the following BUG:

 BUG: Bad page state in process rm  pfn:52e54
 page:ffffea0001222260 count:0 mapcount:0 mapping:          (null) index:0x0
 arch kernel: page flags: 0x4000000000000008(uptodate)

Fix the problem by moving put_io_page() after the SetPageUpdate() call.

Thanks to Hugh Dickins for analyzing this problem.

Reported-by: Markus Trippelsdorf <markus@...ppelsdorf.de>
Tested-by: Markus Trippelsdorf <markus@...ppelsdorf.de>
Signed-off-by: Markus Trippelsdorf <markus@...ppelsdorf.de>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 7f5451c..beacce1 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -237,8 +237,6 @@ static void ext4_end_bio(struct bio *bio, int error)
 			} while (bh != head);
 		}
 
-		put_io_page(io_end->pages[i]);
-
 		/*
 		 * If this is a partial write which happened to make
 		 * all buffers uptodate then we can optimize away a
@@ -248,6 +246,8 @@ static void ext4_end_bio(struct bio *bio, int error)
 		 */
 		if (!partial_write)
 			SetPageUptodate(page);
+
+		put_io_page(io_end->pages[i]);
 	}
 	io_end->num_io_pages = 0;
 	inode = io_end->inode;
--
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