From: Andrew Morton <akpm@linux-foundation.org>
To: Dave Hansen <haveblue@us.ibm.com>
Cc: linux-kernel@vger.kernel.org, hch@infradead.org
Subject: Re: [PATCH 24/25] r/o bind mounts: track number of mount writers
Date: Sun, 23 Sep 2007 23:17:13 -0700 [thread overview]
Message-ID: <20070923231713.f81ee0db.akpm@linux-foundation.org> (raw)
In-Reply-To: <20070920195320.38C8E20D@kernel>
On Thu, 20 Sep 2007 12:53:20 -0700 Dave Hansen <haveblue@us.ibm.com> wrote:
> This is the real meat of the entire series. It actually
> implements the tracking of the number of writers to a mount.
> However, it causes scalability problems because there can
> be hundreds of cpus doing open()/close() on files on the
> same mnt at the same time. Even an atomic_t in the mnt
> has massive scalaing problems because the cacheline gets
> so terribly contended.
>
> This uses a statically-allocated percpu variable. All
> operations are local to a cpu as long that cpu operates on
> the same mount, and there are no writer count imbalances.
> Writer count imbalances happen when a write is taken on one
> cpu, and released on another, like when an open/close pair
> is performed on two different cpus because the task moved.
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.
next prev parent reply other threads:[~2007-09-24 6:17 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-20 19:52 [PATCH 00/25] Read-only bind mounts Dave Hansen
2007-09-20 19:52 ` [PATCH 01/25] filesystem helpers for custom 'struct file's Dave Hansen
2007-09-20 19:52 ` [PATCH 02/25] rearrange may_open() to be r/o friendly Dave Hansen
2007-09-20 19:52 ` [PATCH 03/25] give may_open() a local 'mnt' variable Dave Hansen
2007-09-20 19:57 ` Christoph Hellwig
2007-09-20 19:52 ` [PATCH 04/25] create cleanup helper svc_msnfs() Dave Hansen
2007-09-20 19:52 ` [PATCH 05/25] r/o bind mounts: stub functions Dave Hansen
2007-09-20 19:52 ` [PATCH 06/25] elevate write count open()'d files Dave Hansen
2007-11-28 8:41 ` Andrew Morton
2007-11-28 17:33 ` Dave Hansen
2007-09-20 19:52 ` [PATCH 07/25] r/o bind mounts: elevate write count for some ioctls Dave Hansen
2007-09-21 8:17 ` Andrew Morton
2007-09-21 21:15 ` Dave Hansen
2007-09-26 1:34 ` [RFC] detect missed mnt_want_write() calls Dave Hansen
2007-09-21 23:03 ` [PATCH 07/25] r/o bind mounts: elevate write count for some ioctls Andrew Morton
2007-09-21 23:39 ` Dave Hansen
2007-09-21 23:47 ` Andrew Morton
2007-09-20 19:52 ` [PATCH 08/25] elevate writer count for chown and friends Dave Hansen
2007-09-20 19:53 ` [PATCH 09/25] make access() use mnt check Dave Hansen
2007-09-20 19:53 ` [PATCH 10/25] elevate mnt writers for callers of vfs_mkdir() Dave Hansen
2007-09-20 19:53 ` [PATCH 11/25] elevate write count during entire ncp_ioctl() Dave Hansen
2007-09-20 19:53 ` [PATCH 12/25] elevate write count for link and symlink calls Dave Hansen
2007-09-20 19:53 ` [PATCH 13/25] elevate mount count for extended attributes Dave Hansen
2007-09-20 19:53 ` [PATCH 14/25] elevate write count for file_update_time() Dave Hansen
2007-09-20 19:53 ` [PATCH 15/25] unix_find_other() elevate write count for touch_atime() Dave Hansen
2007-09-20 19:53 ` [PATCH 16/25] elevate write count over calls to vfs_rename() Dave Hansen
2007-09-20 19:53 ` [PATCH 17/25] nfs: check mnt instead of superblock directly Dave Hansen
2007-09-20 19:53 ` [PATCH 18/25] elevate writer count for do_sys_truncate() Dave Hansen
2007-09-20 19:53 ` [PATCH 19/25] elevate write count for do_utimes() Dave Hansen
2007-09-20 19:53 ` [PATCH 20/25] elevate write count for do_sys_utime() and touch_atime() Dave Hansen
2007-09-20 19:53 ` [PATCH 21/25] sys_mknodat(): elevate write count for vfs_mknod/create() Dave Hansen
2007-09-20 19:53 ` [PATCH 22/25] elevate mnt writers for vfs_unlink() callers Dave Hansen
2007-09-20 19:53 ` [PATCH 23/25] do_rmdir(): elevate write count Dave Hansen
2007-09-20 19:53 ` [PATCH 24/25] r/o bind mounts: track number of mount writers Dave Hansen
2007-09-24 6:17 ` Andrew Morton [this message]
2007-09-24 14:34 ` Arjan van de Ven
2007-09-24 22:06 ` Dave Hansen
2007-09-24 22:25 ` Andrew Morton
2007-09-24 23:05 ` Dave Hansen
2007-09-24 23:15 ` Andrew Morton
2007-09-25 16:10 ` Dave Hansen
2007-09-24 17:54 ` Christoph Hellwig
2007-09-24 19:10 ` Andrew Morton
2007-09-24 19:24 ` Christoph Hellwig
2007-09-24 19:28 ` Dave Hansen
2007-09-24 19:42 ` Andrew Morton
2007-10-01 18:06 ` Dave Hansen
2007-09-20 19:53 ` [PATCH 25/25] honor r/w changes at do_remount() time Dave Hansen
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