From: Hugh Dickins <hughd@google.com>
To: Christoph Hellwig <hch@lst.de>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: + writeback-split-inode_wb_list_lock-into-bdi_writebacklist_lock-fix-f ix.patch added to -mm tree
Date: Wed, 4 May 2011 11:42:53 -0700 [thread overview]
Message-ID: <BANLkTi=bfpOyCPPZBj8QkDzUPeRf=Cfcqg@mail.gmail.com> (raw)
In-Reply-To: <20110504094930.GA30358@lst.de>
On Wed, May 4, 2011 at 2:49 AM, Christoph Hellwig <hch@lst.de> wrote:
> On Tue, May 03, 2011 at 01:57:44PM -0700, akpm@linux-foundation.org wrote:
>> struct backing_dev_info *old = inode->i_data.backing_dev_info;
>>
>> - if (dst == old)
>> + if (dst == old) /* deadlock avoidance */
>
> That's not an overly useful comment. It should be a proper block coment
> documentation how that we could ever end up with the same bdi as
> destination and source.
I didn't put in a comment myself because it seemed obvious that we'd
want to avoid calling something named bdi_lock_two(a, b) when a and b
are the same; and I was expecting it to be obvious to you that
actually we could get here with a and b the same. But apparently not.
default_backing_dev_info?
>
> Which is something I wanted to ask Hugh anyway - do you have traces explaining
> how this happens for you?
Let's take out the patch and jot down the dmesg, omitting ? stale
lines and function offsets from the backtrace.
Something that may prove relevant: this is openSUSE 11.4, which cannot
boot my kernels unless I have CONFIG_DEVTMPFS=y; and I've set
CONFIG_DEVTMPFS_MOUNT=y too. No initramfs.
...
VFS: Mounted root (ext2 filesystem) readonly on device 8:1.
devtmpfs: mounted
Freeing unused kernel memory: 352k freed
udev[162]: starting version 166
BUG: spinlock recursion on CPU#0, blkid/299
lock: 78690c30, .magic: dead4ead, .owner: blkid/299, .owner_cpu: 0
Pid: 299, comm: blkid Not tainted 2.6.39-rc5-mm1 #4
Call Trace:
spin_bug
do_raw_spin_lock
_raw_spin_lock_nested
bdi_lock_two
bdev_inode_switch_bdi
__blkdev_get
blkdev_get
blkdev_open
__dentry_open
nameidata_to_filp
do_last
path_openat
do_filp_open
do_sys_open
sys_open
sysenter_do_call
And indeed that "lock: 78690c30" falls inside my
default_backing_dev_info at 78690ae4.
Hugh
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prev parent reply other threads:[~2011-05-04 18:42 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <201105032057.p43Kvj4C009848@imap1.linux-foundation.org>
2011-05-04 9:49 ` + writeback-split-inode_wb_list_lock-into-bdi_writebacklist_lock-fix-f ix.patch added to -mm tree Christoph Hellwig
2011-05-04 18:42 ` Hugh Dickins [this message]
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