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Date: Mon, 2 Jul 2012 11:32:45 +0200
From: Jan Kara <jack@...e.cz>
To: Jeff Liu <jeff.liu@...cle.com>
Cc: linux-serial@...r.kernel.org,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
gregkh@...uxfoundation.org, Jan Kara <jack@...e.cz>,
Ted Ts'o <tytso@....edu>
Subject: Re: [PATCH 0/2] Fix potential dead lock for tty_write_message() if
CONFIG_PRINT_QUOTA_WARNING is enabled
Hello,
On Sat 30-06-12 17:39:45, Jeff Liu wrote:
> I observed the below lockdep warning info at syslog on 3.5-rc4, it could be simply reproduced by creating
> files more than the soft limits of inode quota on ext4 if CONFIG_PRINT_QUOTA_WARNING is enabled.
>
> jeff@...roch:~$ uname -a
> Linux pibroch 3.5.0-rc4-dirty #220 SMP Fri Jun 29 11:30:20 CST 2012 i686 GNU/Linux
> jeff@...roch:~$ quota -u jeff
> Disk quotas for user jeff (uid 1000):
> Filesystem blocks quota limit grace files quota limit grace
> /dev/sda8 0 0 0 1 100 6000
>
> So creating 110 a files could got quota warns.
> $ for((i=0;i<110;i++));do touch "/ext4_mount_path/testme.".$i;done
Yeah, situations like the one reported below can possibly cause problems
(e.g. when you have application with redirected output to /mnt/out and the
application writes to /mnt/b which exceeds quota - you try to write message
to /mnt/out in the middle of writing to /mnt/b). These problems are rather
hard to overcome and that's why CONFIG_PRINT_QUOTA_WARNING is marked as
obsolete and CONFIG_QUOTA_NETLINK_INTERFACE should be used instead.
Honza
> [ 213.324324] =====================================================
> [ 213.324337] [ INFO: possible circular locking dependency detected ]
> [ 213.324353] 3.5.0-rc4 #201 Not tainted
> [ 213.324364] -------------------------------------------------------
> [ 213.324376] touch/2237 is trying to acquire lock:
> [ 213.324413] (&tty->atomic_write_lock){+.+...}, at: [<c14dcc02>] tty_write_message+0x40/0x103
> [ 213.324426] [ 213.324426] but task is already holding lock:
> [ 213.324469] (jbd2_handle){+.+...}, at: [<f8202060>] start_this_handle+0xa19/0xa8a [jbd2]
> [ 213.324482] [ 213.324482] which lock already depends on the new lock.
> [ 213.324482] [ 213.324497] [ 213.324497] the existing dependency chain (in reverse order) is:
> [ 213.324525] [ 213.324525] -> #2 (jbd2_handle){+.+...}:
> [ 213.324546] [<c1101e89>] lock_acquire+0x198/0x1d3
> [ 213.324576] [<f82020a4>] start_this_handle+0xa5d/0xa8a [jbd2]
> [ 213.324608] [<f820247a>] jbd2__journal_start+0x11b/0x187 [jbd2]
> [ 213.324638] [<f8202506>] jbd2_journal_start+0x20/0x30 [jbd2]
> [ 213.324701] [<f8a8028c>] ext4_journal_start_sb+0x280/0x296 [ext4]
> [ 213.324753] [<f8a5a9bd>] ext4_dirty_inode+0x27/0x84 [ext4]
> [ 213.324767] [<c127e24e>] __mark_inode_dirty+0x52/0x2e7
> [ 213.324781] [<c12675fe>] update_time+0x10f/0x126
> [ 213.324794] [<c1267c07>] touch_atime+0x235/0x25e
> [ 213.324841] [<f8a49fac>] ext4_file_mmap+0x5c/0x7d [ext4]
> [ 213.324856] [<c1201bf9>] mmap_region+0x449/0x7c4
> [ 213.324870] [<c1202435>] do_mmap_pgoff+0x4c1/0x4db
> [ 213.324884] [<c11e7bb4>] vm_mmap_pgoff+0x98/0xc7
> [ 213.324899] [<c11ffa5e>] sys_mmap_pgoff+0x16a/0x1bf
> [ 213.324912] [<c18a5224>] syscall_call+0x7/0xb
>
> [ 213.324929] [ 213.324929] -> #1 (&mm->mmap_sem){++++++}:
> [ 213.324943] [<c1101e89>] lock_acquire+0x198/0x1d3
> [ 213.324956] [<c11f3bcb>] might_fault+0xbf/0xf8
> [ 213.324970] [<c13e1cd3>] _copy_from_user+0x40/0x8a
> [ 213.324982] [<c14da3cf>] copy_from_user+0x16/0x26
> [ 213.324994] [<c14dc80b>] tty_write+0x282/0x3c7
> [ 213.325006] [<c14dca34>] redirected_tty_write+0xe4/0xfd
> [ 213.325020] [<c123f955>] vfs_write+0xf5/0x1a3
> [ 213.325033] [<c123fcb8>] sys_write+0x6c/0xa9
> [ 213.325045] [<c18b169f>] sysenter_do_call+0x12/0x38
>
> [ 213.325062] [ 213.325062] -> #0 (&tty->atomic_write_lock){+.+...}:
> [ 213.325078] [<c1100e70>] __lock_acquire+0x15bb/0x1b98
> [ 213.325091] [<c1101e89>] lock_acquire+0x198/0x1d3
> [ 213.325105] [<c189fb16>] __mutex_lock_common+0x52/0x7cd
> [ 213.325118] [<c18a0439>] mutex_lock_nested+0x5c/0x70
> [ 213.325130] [<c14dcc02>] tty_write_message+0x40/0x103
> [ 213.325144] [<c12bf9fd>] flush_warnings+0x17c/0x313
> [ 213.325157] [<c12c47c4>] dquot_alloc_inode+0x1e4/0x1fc
> [ 213.325207] [<f8a4db1e>] ext4_new_inode+0x11f5/0x1576 [ext4]
> [ 213.325262] [<f8a6166d>] ext4_create+0x160/0x230 [ext4]
> [ 213.325276] [<c1253dc2>] vfs_create+0xc4/0x106
> [ 213.325297] [<c1254ee2>] do_last+0x437/0xdcc
> [ 213.325310] [<c125762a>] path_openat+0x10e/0x5a7
> [ 213.325323] [<c1257c57>] do_filp_open+0x39/0xc2
> [ 213.325335] [<c123e362>] do_sys_open+0xb5/0x1bb
> [ 213.325347] [<c123e4a1>] sys_open+0x39/0x5b
> [ 213.325360] [<c18a5224>] syscall_call+0x7/0xb
> [ 213.325368] [ 213.325368] other info that might help us debug this:
> [ 213.325368] [ 213.325391] Chain exists of:
> [ 213.325391] &tty->atomic_write_lock --> &mm->mmap_sem --> jbd2_handle
> [ 213.325391] [ 213.325401] Possible unsafe locking scenario:
> [ 213.325401] [ 213.325410] CPU0 CPU1
> [ 213.325417] ---- ----
> [ 213.325558] lock(jbd2_handle);
> [ 213.325571] lock(&mm->mmap_sem);
> [ 213.325583] lock(jbd2_handle);
> [ 213.325595] lock(&tty->atomic_write_lock);
> [ 213.325602] [ 213.325602] *** DEADLOCK ***
> [ 213.325602] [ 213.325613] 2 locks held by touch/2237:
> [ 213.325639] #0: (&type->i_mutex_dir_key#3){+.+.+.}, at: [<c1254da1>] do_last+0x2f6/0xdcc
> [ 213.325673] #1: (jbd2_handle){+.+...}, at: [<f8202060>] start_this_handle+0xa19/0xa8a [jbd2]
> [ 213.325682] [ 213.325682] stack backtrace:
> [ 213.325693] Pid: 2237, comm: touch Not tainted 3.5.0-rc4 #201
> [ 213.325702] Call Trace:
> [ 213.325717] [<c10faac9>] print_circular_bug+0x3fa/0x412
> [ 213.325732] [<c1100e70>] __lock_acquire+0x15bb/0x1b98
> [ 213.325747] [<c1101e89>] lock_acquire+0x198/0x1d3
> [ 213.325761] [<c14dcc02>] ? tty_write_message+0x40/0x103
> [ 213.325776] [<c189fb16>] __mutex_lock_common+0x52/0x7cd
> [ 213.325789] [<c14dcc02>] ? tty_write_message+0x40/0x103
> [ 213.325804] [<c18a525d>] ? restore_all+0xf/0xf
> [ 213.325819] [<c10b396c>] ? need_resched+0x22/0x3a
> [ 213.325833] [<c18a0439>] mutex_lock_nested+0x5c/0x70
> [ 213.325847] [<c14dcc02>] ? tty_write_message+0x40/0x103
> [ 213.325860] [<c14dcc02>] tty_write_message+0x40/0x103
> [ 213.325874] [<c12bf9fd>] flush_warnings+0x17c/0x313
> [ 213.325888] [<c12c47c4>] dquot_alloc_inode+0x1e4/0x1fc
> [ 213.325941] [<f8a4db1e>] ext4_new_inode+0x11f5/0x1576 [ext4]
> [ 213.326000] [<f8a6166d>] ext4_create+0x160/0x230 [ext4]
> [ 213.326018] [<c1253dc2>] vfs_create+0xc4/0x106
> [ 213.326033] [<c1254ee2>] do_last+0x437/0xdcc
> [ 213.326048] [<c125762a>] path_openat+0x10e/0x5a7
> [ 213.326063] [<c1257c57>] do_filp_open+0x39/0xc2
> [ 213.326077] [<c1101cdc>] ? lock_release+0x4b3/0x4c8
> [ 213.326090] [<c18a5116>] ? _raw_spin_unlock+0x4c/0x5d
> [ 213.326104] [<c126c821>] ? alloc_fd+0x2fe/0x317
> [ 213.326118] [<c123e362>] do_sys_open+0xb5/0x1bb
> [ 213.326132] [<c123e4a1>] sys_open+0x39/0x5b
> [ 213.326145] [<c18a5224>] syscall_call+0x7/0xb
>
> looks this issue is caused by the tty_write_message()->....->tty_write() because it will call copy_from_user() which will
> produce page faults and kick off ext4 inode dirty process on another CPU if possible.
> According to my understood, if the current process was be preempted when its time quantum expires, the need_resched field of
> the current process is set, so the scheduler is invoked and the current process will be re-scheduled to run and call
> next tty_write_message() at dquot.c->print_warning(), and it need to acquire atomic_write_lock again, however, this lock has
> already been hold by another process, so the race situation is occurred.
>
> I know such kind of issue should be better to fix at quota module, I have also tried to fix it there but no luck. :(
> For now, I could only work out a stupid patch set to let lockdep happy by making both tty_write_lock and BTM lock sleepable.
>
>
> Thanks,
> -Jeff
>
>
>
>
>
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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