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Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

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From: Andrew Morton <akpm@...>
To: Dave Hansen <haveblue@...>
Cc: <linux-kernel@...>, <hch@...>
Subject: Re: [PATCH 24/25] r/o bind mounts: track number of mount writers
Date: Monday, September 24, 2007 - 2:17 am

On Thu, 20 Sep 2007 12:53:20 -0700 Dave Hansen <haveblue@us.ibm.com> wrote:



Did you test with lockdep enabled?

=============================================
[ INFO: possible recursive locking detected ]
2.6.23-rc7-mm1 #1
---------------------------------------------
swapper/1 is trying to acquire lock:
 (&writer->lock){--..}, at: [<c0197a32>] lock_and_coalesce_cpu_mnt_writer_counts+0x32/0x70

but task is already holding lock:
 (&writer->lock){--..}, at: [<c0197a32>] lock_and_coalesce_cpu_mnt_writer_counts+0x32/0x70

other info that might help us debug this:
1 lock held by swapper/1:
 #0:  (&writer->lock){--..}, at: [<c0197a32>] lock_and_coalesce_cpu_mnt_writer_counts+0x32/0x70

stack backtrace:
 [<c0103ffa>] show_trace_log_lvl+0x1a/0x30
 [<c0104b82>] show_trace+0x12/0x20
 [<c0104c96>] dump_stack+0x16/0x20
 [<c0144dc5>] __lock_acquire+0xde5/0x10a0
 [<c01450fa>] lock_acquire+0x7a/0xa0
 [<c03e734c>] _spin_lock+0x2c/0x40
 [<c0197a32>] lock_and_coalesce_cpu_mnt_writer_counts+0x32/0x70
 [<c01982c6>] mntput_no_expire+0x36/0xc0
 [<c0188f15>] path_release_on_umount+0x15/0x20
 [<c0198930>] sys_umount+0x40/0x230
 [<c010070b>] name_to_dev_t+0x9b/0x270
 [<c05230c2>] prepare_namespace+0x62/0x1b0
 [<c05226ca>] kernel_init+0x21a/0x320
 [<c0103b47>] kernel_thread_helper+0x7/0x10
 =======================

It look like a false positive to me, but really, for a patchset of this
complexity and maturity I cannot fathom how it could have escaped any
lockdep testing.

-
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Messages in current thread:
[PATCH 00/25] Read-only bind mounts, Dave Hansen, (Thu Sep 20, 3:52 pm)
[PATCH 24/25] r/o bind mounts: track number of mount writers, Dave Hansen, (Thu Sep 20, 3:53 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Christoph Hellwig, (Mon Sep 24, 1:54 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Dave Hansen, (Mon Sep 24, 3:28 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Andrew Morton, (Mon Sep 24, 3:42 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Dave Hansen, (Mon Oct 1, 2:06 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Andrew Morton, (Mon Sep 24, 3:10 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Christoph Hellwig, (Mon Sep 24, 3:24 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Andrew Morton, (Mon Sep 24, 2:17 am)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Dave Hansen, (Mon Sep 24, 6:06 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Andrew Morton, (Mon Sep 24, 6:25 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Dave Hansen, (Mon Sep 24, 7:05 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Andrew Morton, (Mon Sep 24, 7:15 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Dave Hansen, (Tue Sep 25, 12:10 pm)
Re: [PATCH 24/25] r/o bind mounts: track number of mount wri..., Arjan van de Ven, (Mon Sep 24, 10:34 am)
[PATCH 25/25] honor r/w changes at do_remount() time, Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 23/25] do_rmdir(): elevate write count, Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 22/25] elevate mnt writers for vfs_unlink() callers, Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 21/25] sys_mknodat(): elevate write count for vfs_mkn..., Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 13/25] elevate mount count for extended attributes, Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 06/25] elevate write count open()'d files, Dave Hansen, (Thu Sep 20, 3:52 pm)
Re: [PATCH 06/25] elevate write count open()'d files, Andrew Morton, (Wed Nov 28, 4:41 am)
Re: [PATCH 06/25] elevate write count open()'d files, Dave Hansen, (Wed Nov 28, 1:33 pm)
[PATCH 20/25] elevate write count for do_sys_utime() and tou..., Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 19/25] elevate write count for do_utimes(), Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 18/25] elevate writer count for do_sys_truncate(), Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 14/25] elevate write count for file_update_time(), Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 17/25] nfs: check mnt instead of superblock directly, Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 02/25] rearrange may_open() to be r/o friendly, Dave Hansen, (Thu Sep 20, 3:52 pm)
[PATCH 16/25] elevate write count over calls to vfs_rename(), Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 15/25] unix_find_other() elevate write count for touc..., Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 10/25] elevate mnt writers for callers of vfs_mkdir(), Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 07/25] r/o bind mounts: elevate write count for some ..., Dave Hansen, (Thu Sep 20, 3:52 pm)
Re: [PATCH 07/25] r/o bind mounts: elevate write count for s..., Andrew Morton, (Fri Sep 21, 7:03 pm)
Re: [PATCH 07/25] r/o bind mounts: elevate write count for s..., Dave Hansen, (Fri Sep 21, 7:39 pm)
Re: [PATCH 07/25] r/o bind mounts: elevate write count for s..., Andrew Morton, (Fri Sep 21, 7:47 pm)
Re: [PATCH 07/25] r/o bind mounts: elevate write count for s..., Andrew Morton, (Fri Sep 21, 4:17 am)
[RFC] detect missed mnt_want_write() calls, Dave Hansen, (Tue Sep 25, 9:34 pm)
Re: [PATCH 07/25] r/o bind mounts: elevate write count for s..., Dave Hansen, (Fri Sep 21, 5:15 pm)
[PATCH 08/25] elevate writer count for chown and friends, Dave Hansen, (Thu Sep 20, 3:52 pm)
[PATCH 12/25] elevate write count for link and symlink calls, Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 11/25] elevate write count during entire ncp_ioctl(), Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 09/25] make access() use mnt check, Dave Hansen, (Thu Sep 20, 3:53 pm)
[PATCH 05/25] r/o bind mounts: stub functions, Dave Hansen, (Thu Sep 20, 3:52 pm)
[PATCH 04/25] create cleanup helper svc_msnfs(), Dave Hansen, (Thu Sep 20, 3:52 pm)
[PATCH 03/25] give may_open() a local 'mnt' variable, Dave Hansen, (Thu Sep 20, 3:52 pm)
Re: [PATCH 03/25] give may_open() a local 'mnt' variable, Christoph Hellwig, (Thu Sep 20, 3:57 pm)
[PATCH 01/25] filesystem helpers for custom 'struct file's, Dave Hansen, (Thu Sep 20, 3:52 pm)