From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755657Ab0CLANf (ORCPT ); Thu, 11 Mar 2010 19:13:35 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:33786 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753325Ab0CLANd (ORCPT ); Thu, 11 Mar 2010 19:13:33 -0500 Subject: vfs-scalability: odd null pointer issue in link_path_walk From: john stultz To: Nick Piggin , Thomas Gleixner Cc: lkml , Clark Williams , John Kacur Content-Type: text/plain; charset="UTF-8" Date: Thu, 11 Mar 2010 16:13:25 -0800 Message-ID: <1268352805.3475.60.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey Nick, So yesterday I came across an odd null pointer oops in link_path_walk: BUG: unable to handle kernel NULL pointer dereference at 0000000000000030 IP: [] link_path_walk+0xd12/0xda0 PGD 42b12e067 PUD 42cb2a067 PMD 0 Oops: 0000 [#1] PREEMPT SMP last sysfs file: /sys/block/md0/dev CPU 7 Pid: 2993, comm: vgs Not tainted 2.6.33-rc8john #272 Server Blade/IBM eServer BladeCenter HS21 -[7995AC1]- RIP: 0010:[] [] link_path_walk+0xd12/0xda0 RSP: 0018:ffff88042a929b78 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff88042ab41000 RCX: ffff88042ab41028 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88042aa0fcc0 RBP: ffff88042a929c28 R08: ffff88042aa0fcc0 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: ffff88042c6a40b0 R13: 0000000000000000 R14: 0000000000000000 R15: ffff88042a929dc8 FS: 00007f6f8c481710(0000) GS:ffff8800283c0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 0000000000000030 CR3: 000000042b310000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process vgs (pid: 2993, threadinfo ffff88042a928000, task ffff88042ab41000) Stack: ffff88042ab41000 ffff88042ab41000 ffff88042ab41000 ffff88042ab41000 <0> 0000000100000000 ffff88042a929de8 ffff880400000000 0000000000000000 <0> ffff88042f6b5610 0000000000000000 0000000000000000 ffff88042f418920 Call Trace: [] ? path_get+0x32/0x50 [] link_path_walk+0xc20/0xda0 [] ? path_get+0x32/0x50 [] path_walk+0x5c/0xd0 [] do_path_lookup+0x1ee/0x250 [] ? do_path_lookup+0x0/0x250 [] user_path_at+0x7b/0xb0 [] ? vfsmount_read_unlock+0x31/0x60 [] ? mntput_no_expire+0x48/0x190 [] ? cp_new_stat+0xe3/0xf0 [] vfs_fstatat+0x3c/0x80 [] vfs_stat+0x16/0x20 [] sys_newstat+0x1f/0x50 [] ? lockdep_sys_exit_thunk+0x35/0x67 [] system_call_fastpath+0x16/0x1b Code: ec e8 93 c8 ff ff 0f 1f 00 e9 46 ff ff ff 41 83 7f 34 04 66 0f 1f 44 00 00 0f 85 38 ff ff ff 4d 8b 67 08 49 8b 84 24 b8 00 00 00 <48> 8b 40 30 f6 40 09 40 0f 84 1e ff ff ff 49 8b 44 24 70 4c 89 RIP [] link_path_walk+0xd12/0xda0 RSP CR2: 0000000000000030 ---[ end trace 0dd94d94b1b27094 ]--- I'd never seen it before in all my test runs, but it was triggering 100% of the time, and it seems to be somehow connected to me adding an xfs partition to the box (even if it wasn't mounted and more oddly, even after i reformatted that partition as ext3). Anyway, I bisected the change down to your fs-scale-pseudo patch and reverting it does keep the issue from happening. Not sure if you can think of a quick fix here, but I'm thinking I might revert this patch from my version of your patchset for now. thanks -john