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Subject: Re: Oops with DCACHE_WORD_ACCESS and ocfs2, autofs4
From: Jana Saout <jana@saout.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Nick Piggin <npiggin@gmail.com>, Joel Becker <jlbec@evilplan.org>,
        linux-kernel@vger.kernel.org
Date: Thu, 03 May 2012 22:30:35 +0200
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Hello,

> Jana - never mind that patch. It will avoid the page fault, but try to
> use the wrong (truncated) name due to the extraneous left-shift of the
> loaded value.
> 
> So use the attached one instead. It just removes the extra shift that
> Peter noticed, and also allows the use of the word-at-a-time code with
> DEBUG_PAGEALLOC so that I can test it myself too.

Ok, I have been running with that patch for slightly over an hour and
didn't get that oops anymore.

Instead, now I got an oops on __d_lookup (fs/dcache.c line 155) (kernel
log excerpt below):

> #ifdef CONFIG_DCACHE_WORD_ACCESS
>         unsigned long a,b,mask;
> 
>         if (unlikely(scount != tcount))
>                 return 1;
> 
>         for (;;) {
>                 a = *(unsigned long *)cs;
>     ->          b = *(unsigned long *)ct;  
>                 if (tcount < sizeof(unsigned long))
>                         break;

Similar issue, ct is pointing at 0xffff880115a59ffb

	Jana


BUG: unable to handle kernel paging request at ffff880115a5a000
IP: [<ffffffff81146850>] __d_lookup+0xe0/0x170
PGD 180c067 PUD bf3f4067 PMD bf4a2067 PTE 0
Oops: 0000 [#1] PREEMPT SMP 
CPU 0 
Modules linked in: nfs lockd auth_rpcgss nfs_acl sunrpc autofs4 ocfs2
jbd2 ocfs2_dlmfs ocfs2_stack_o2cb ocfs2_dlm ocfs2_nodemanager
ocfs2_stackglue configfs

Pid: 10310, comm: apache2 Not tainted 3.4.0-js1-test #1  
RIP: e030:[<ffffffff81146850>]  [<ffffffff81146850>] __d_lookup
+0xe0/0x170
RSP: e02b:ffff880095cc9bf8  EFLAGS: 00010293
RAX: 0000000000006461 RBX: ffff88009d3ef248 RCX: 0000000000000002
RDX: 0000000000000006 RSI: 0000000000000000 RDI: ffff88009d3ef29c
RBP: 0000000000007374 R08: 0000000000000002 R09: ffff88009d3ef278
R10: ffff88009d3ef240 R11: 0000000000000000 R12: ffff88009d3ef29c
R13: ffff880065148e40 R14: ffff880115a59ffb R15: ffff880095cc9e78
FS:  00007fcb26ffe6d0(0000) GS:ffff8800bff0c000(0000)
knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: ffff880115a5a000 CR3: 0000000095cc2000 CR4: 0000000000000660
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process apache2 (pid: 10310, threadinfo ffff880095cc8000, task
ffff8800b3de1800)
Stack:
 ffffffff814268da 000000000000e030 0000000000010257 0000000000000002
 000000000000e02b ffff880095cc9d10 ffff880095cc9d40 ffff880095cc9e68
 0000000000000001 0000000000000000 ffff8800b3de1800 ffffffff8113c135
Call Trace:
 [<ffffffff814268da>] ? bad_gs+0xa34/0x197a
 [<ffffffff8113c135>] ? do_lookup+0x165/0x340
 [<ffffffff8113c7ba>] ? link_path_walk+0x4aa/0x890
 [<ffffffff81036c52>] ? pvclock_clocksource_read+0x52/0xf0
 [<ffffffff8113cd02>] ? path_lookupat+0x52/0x740
 [<ffffffff8104bad1>] ? sys_gettimeofday+0x31/0x80
 [<ffffffff8101a2eb>] ? emulate_vsyscall+0x31b/0x350
 [<ffffffff8113d41c>] ? do_path_lookup+0x2c/0xc0
 [<ffffffff8113aa2d>] ? getname_flags+0xed/0x260
 [<ffffffff8113ebde>] ? user_path_at_empty+0x5e/0xb0
 [<ffffffff8104c912>] ? local_bh_enable_ip+0x22/0xb0
 [<ffffffff81325eeb>] ? sock_setsockopt+0x8b/0x870
 [<ffffffff8112e981>] ? sys_faccessat+0xa1/0x1c0
 [<ffffffff814241f9>] ? system_call_fastpath+0x16/0x1b
Code: 8d 53 f8 44 8b 43 1c 4c 8b 4b 20 75 4e 48 8b 4c 24 18 4d 63 c0 4c
39 c1 75 b0 31 f6 0f 1f 80 00 00 00 00 48 83 f9 07 49 8b 04 31 <49> 8b
14 36 76 5a 48 39 d0 75 94 48 83 c6 08 48 83 e9 08 75 e3 
RIP  [<ffffffff81146850>] __d_lookup+0xe0/0x170
 RSP <ffff880095cc9bf8>
CR2: ffff880115a5a000
---[ end trace b53471b6e52caa9d ]---

(followed by note: apache2[10310] exited with preempt_count 1
BUG: scheduling while atomic: apache2/10310/0x10000002)


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