linux-ext4 - Re: [PATCH] ext4: take i_mutex in ext4_symlink to eliminate a warning from ext4

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Message-ID: <20130327140250.GA4316@gmail.com>
Date:	Wed, 27 Mar 2013 22:02:50 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH] ext4: take i_mutex in ext4_symlink to eliminate a
 warning from ext4_truncate

On Wed, Mar 27, 2013 at 09:41:10AM -0400, Theodore Ts'o wrote:
> On Wed, Mar 27, 2013 at 09:19:07PM +0800, Zheng Liu wrote:
> > From: Zheng Liu <wenqing.lz@...bao.com>
> > 
> > After applied this commit (8e4061cb), we will get a warning from
> > ext4_truncate when i_mutex isn't taken.  Here the assumption is that
> > i_mutex should be taken when we do a truncation.  In ext4_symlink we
> > could need to call ext4_truncate to trim some blocks beyond i_size, but
> > the i_mutex isn't taken.
> 
> Hmm, and this is why I added the warning.  Even after looking your
> patch, I'm having trouble finding the codepath that results in
> ext4_truncate() getting called from __page_symlink().  Can you send
> the stack trace from the WARN_ON, just so I can see what I missed?

Here it is.

kernel: ------------[ cut here ]------------
kernel: WARNING: at fs/ext4/inode.c:3803 ext4_truncate+0x36/0x2d7 [ext4]()
kernel: Hardware name: OptiPlex 780
kernel: Modules linked in: ext4(O) jbd2 crc16 cpufreq_ondemand ipv6
dm_mirror dm_region_hash dm_log dm_mod parport_pc parport dcdbas
acpi_cpufreq mperf serio_raw button pcspkr i2c_i801 sg ehci_pci
ehci_hcd e1000e ptp pps_core ext3 jbd sd_mod ahci libahci libata
scsi_mod uhci_hcd radeon ttm drm_kms_helper drm hwmon i2c_algo_bit i2
c_core [last unloaded: crc16]
kernel: Pid: 4152, comm: fsstress Tainted: G W  O 3.9.0-rc4+ #6
kernel: Call Trace:
kernel: [<ffffffff82031e14>] warn_slowpath_common+0x85/0x9f
kernel: [<ffffffff82031e48>] warn_slowpath_null+0x1a/0x1c
kernel: [<ffffffffa044b789>] ext4_truncate+0x36/0x2d7 [ext4]
kernel: [<ffffffffa044c9a5>] ext4_write_begin+0x35f/0x3b9 [ext4]
kernel: [<ffffffff820af514>] pagecache_write_begin+0x1c/0x1e
kernel: [<ffffffff820f5f80>] __page_symlink+0x6d/0x10f
kernel: [<ffffffffa0450806>] ?  ext4_orphan_add+0x1ea/0x219 [ext4]
kernel: [<ffffffffa0451a7f>] ext4_symlink+0x1ca/0x33e [ext4]
kernel: [<ffffffff820f8c41>] vfs_symlink+0x7c/0xd6
kernel: [<ffffffff820fb634>] sys_symlinkat+0x68/0xb9
kernel: [<ffffffff820fb69b>] sys_symlink+0x16/0x18
kernel: [<ffffffff8238fac2>] system_call_fastpath+0x16/0x1b
kernel: ---[ end trace 05d179cc296c4f3a ]---

Regards,
                                                - Zheng
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