Re: [PATCHv3 9/9] zram: add dynamic device add/remove functionality

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

On (04/30/15 15:34), Sergey Senozhatsky wrote:
> > Isn't it related to bd_mutex?
> 
> I think it is:
> 

I meant: I think it's related

> [  216.713922]  Possible unsafe locking scenario:
> [  216.713923]        CPU0                    CPU1
> [  216.713924]        ----                    ----
> [  216.713925]   lock(&bdev->bd_mutex);
> [  216.713927]                                lock(s_active#162);
> [  216.713929]                                lock(&bdev->bd_mutex);
> [  216.713930]   lock(s_active#162);
> [  216.713932] 
>                 *** DEADLOCK ***
> 
> > I think the problem of deadlock is that you are trying to remove sysfs file
> > in sysfs handler.
> > 
> > #> echo 1 > /sys/xxx/zram_remove
> > 
> > kernfs_fop_write - hold s_active
> >   -> zram_remove_store
> >     -> zram_remove
> >       -> sysfs_remove_group - hold s_active *again*
> > 
> > Right?
> > 
> 
> are those same s_active locks?
> 

I meant: sysfs handler, s_active locks are from different kernfs nodes.
it should be fine: we remove sysfs group from another sysfs group's handler
(zram_control_class_attrs removes zram_disk_attr_group).

	-ss

> 
> we hold (s_active#163) and (&bdev->bd_mutex) and want to acquire (s_active#162)
> 
> [  216.713934] 5 locks held by bash/342:
> [  216.713935]  #0:  (sb_writers#5){.+.+.+}, at: [<ffffffff811508a1>] vfs_write+0xaf/0x145
> [  216.713938]  #1:  (&of->mutex){+.+.+.}, at: [<ffffffff811af1d3>] kernfs_fop_write+0x9c/0x14c
> [  216.713942]  #2:  (s_active#163){.+.+.+}, at: [<ffffffff811af1dc>] kernfs_fop_write+0xa5/0x14c
> [  216.713946]  #3:  (zram_index_mutex){+.+.+.}, at: [<ffffffffa022276f>] zram_remove_store+0x45/0xba [zram]
> [  216.713950]  #4:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffffa022267b>] zram_remove+0x41/0xf0 [zram]
> 
> 
> full log:
> 
> [  216.713826] ======================================================
> [  216.713827] [ INFO: possible circular locking dependency detected ]
> [  216.713829] 4.1.0-rc1-next-20150430-dbg-00010-ga86accf-dirty #121 Tainted: G           O   
> [  216.713831] -------------------------------------------------------
> [  216.713832] bash/342 is trying to acquire lock:
> [  216.713833]  (s_active#162){++++.+}, at: [<ffffffff811ae88d>] kernfs_remove_by_name_ns+0x70/0x8c
> [  216.713840] 
>                but task is already holding lock:
> [  216.713842]  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffffa022267b>] zram_remove+0x41/0xf0 [zram]
> [  216.713846] 
>                which lock already depends on the new lock.
> 
> [  216.713848] 
>                the existing dependency chain (in reverse order) is:
> [  216.713849] 
>                -> #1 (&bdev->bd_mutex){+.+.+.}:
> [  216.713852]        [<ffffffff8107d806>] __lock_acquire+0x10c2/0x11cb
> [  216.713856]        [<ffffffff8107e11c>] lock_acquire+0x13d/0x250
> [  216.713858]        [<ffffffff81528fc6>] mutex_lock_nested+0x5e/0x35f
> [  216.713860]        [<ffffffff81184148>] revalidate_disk+0x4b/0x7c
> [  216.713863]        [<ffffffffa02224d0>] disksize_store+0x1b1/0x1f4 [zram]
> [  216.713866]        [<ffffffff813f8994>] dev_attr_store+0x19/0x23
> [  216.713870]        [<ffffffff811afd84>] sysfs_kf_write+0x48/0x54
> [  216.713872]        [<ffffffff811af238>] kernfs_fop_write+0x101/0x14c
> [  216.713874]        [<ffffffff811502c2>] __vfs_write+0x26/0xbe
> [  216.713877]        [<ffffffff811508b2>] vfs_write+0xc0/0x145
> [  216.713879]        [<ffffffff81150fd0>] SyS_write+0x51/0x8f
> [  216.713881]        [<ffffffff8152d097>] system_call_fastpath+0x12/0x6f
> [  216.713884] 
>                -> #0 (s_active#162){++++.+}:
> [  216.713886]        [<ffffffff8107b69e>] check_prevs_add+0x19e/0x747
> [  216.713889]        [<ffffffff8107d806>] __lock_acquire+0x10c2/0x11cb
> [  216.713891]        [<ffffffff8107e11c>] lock_acquire+0x13d/0x250
> [  216.713892]        [<ffffffff811adac4>] __kernfs_remove+0x1b6/0x2cd
> [  216.713895]        [<ffffffff811ae88d>] kernfs_remove_by_name_ns+0x70/0x8c
> [  216.713897]        [<ffffffff811b0872>] remove_files+0x42/0x67
> [  216.713899]        [<ffffffff811b0b39>] sysfs_remove_group+0x69/0x88
> [  216.713901]        [<ffffffffa02226a0>] zram_remove+0x66/0xf0 [zram]
> [  216.713904]        [<ffffffffa02227bf>] zram_remove_store+0x95/0xba [zram]
> [  216.713906]        [<ffffffff813fe053>] class_attr_store+0x1c/0x26
> [  216.713909]        [<ffffffff811afd84>] sysfs_kf_write+0x48/0x54
> [  216.713911]        [<ffffffff811af238>] kernfs_fop_write+0x101/0x14c
> [  216.713913]        [<ffffffff811502c2>] __vfs_write+0x26/0xbe
> [  216.713915]        [<ffffffff811508b2>] vfs_write+0xc0/0x145
> [  216.713917]        [<ffffffff81150fd0>] SyS_write+0x51/0x8f
> [  216.713918]        [<ffffffff8152d097>] system_call_fastpath+0x12/0x6f
> [  216.713920] 
>                other info that might help us debug this:
> 
> [  216.713922]  Possible unsafe locking scenario:
> 
> [  216.713923]        CPU0                    CPU1
> [  216.713924]        ----                    ----
> [  216.713925]   lock(&bdev->bd_mutex);
> [  216.713927]                                lock(s_active#162);
> [  216.713929]                                lock(&bdev->bd_mutex);
> [  216.713930]   lock(s_active#162);
> [  216.713932] 
>                 *** DEADLOCK ***
> 
> [  216.713934] 5 locks held by bash/342:
> [  216.713935]  #0:  (sb_writers#5){.+.+.+}, at: [<ffffffff811508a1>] vfs_write+0xaf/0x145
> [  216.713938]  #1:  (&of->mutex){+.+.+.}, at: [<ffffffff811af1d3>] kernfs_fop_write+0x9c/0x14c
> [  216.713942]  #2:  (s_active#163){.+.+.+}, at: [<ffffffff811af1dc>] kernfs_fop_write+0xa5/0x14c
> [  216.713946]  #3:  (zram_index_mutex){+.+.+.}, at: [<ffffffffa022276f>] zram_remove_store+0x45/0xba [zram]
> [  216.713950]  #4:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffffa022267b>] zram_remove+0x41/0xf0 [zram]
> [  216.713954] 
>                stack backtrace:
> [  216.713957] CPU: 1 PID: 342 Comm: bash Tainted: G           O    4.1.0-rc1-next-20150430-dbg-00010-ga86accf-dirty #121
> [  216.713958] Hardware name: SAMSUNG ELECTRONICS CO.,LTD Samsung DeskTop System/Samsung DeskTop System, BIOS 05CC                   04/09/2010
> [  216.713960]  ffffffff82400210 ffff8800ba367a28 ffffffff815265b1 ffffffff810785f2
> [  216.713962]  ffffffff8242f970 ffff8800ba367a78 ffffffff8107aac7 ffffffff817bd85e
> [  216.713965]  ffff8800bdeca1a0 ffff8800bdeca9c0 ffff8800bdeca998 ffff8800bdeca9c0
> [  216.713967] Call Trace:
> [  216.713971]  [<ffffffff815265b1>] dump_stack+0x4c/0x6e
> [  216.713973]  [<ffffffff810785f2>] ? up+0x39/0x3e
> [  216.713975]  [<ffffffff8107aac7>] print_circular_bug+0x2b1/0x2c2
> [  216.713976]  [<ffffffff8107b69e>] check_prevs_add+0x19e/0x747
> [  216.713979]  [<ffffffff8107d806>] __lock_acquire+0x10c2/0x11cb
> [  216.713981]  [<ffffffff8107e11c>] lock_acquire+0x13d/0x250
> [  216.713983]  [<ffffffff811ae88d>] ? kernfs_remove_by_name_ns+0x70/0x8c
> [  216.713985]  [<ffffffff811adac4>] __kernfs_remove+0x1b6/0x2cd
> [  216.713987]  [<ffffffff811ae88d>] ? kernfs_remove_by_name_ns+0x70/0x8c
> [  216.713989]  [<ffffffff811adca8>] ? kernfs_find_ns+0xcd/0x10e
> [  216.713990]  [<ffffffff81529294>] ? mutex_lock_nested+0x32c/0x35f
> [  216.713992]  [<ffffffff811ae88d>] kernfs_remove_by_name_ns+0x70/0x8c
> [  216.713994]  [<ffffffff811b0872>] remove_files+0x42/0x67
> [  216.713996]  [<ffffffff811b0b39>] sysfs_remove_group+0x69/0x88
> [  216.713999]  [<ffffffffa02226a0>] zram_remove+0x66/0xf0 [zram]
> [  216.714001]  [<ffffffffa02227bf>] zram_remove_store+0x95/0xba [zram]
> [  216.714003]  [<ffffffff813fe053>] class_attr_store+0x1c/0x26
> [  216.714005]  [<ffffffff811afd84>] sysfs_kf_write+0x48/0x54
> [  216.714007]  [<ffffffff811af238>] kernfs_fop_write+0x101/0x14c
> [  216.714009]  [<ffffffff811502c2>] __vfs_write+0x26/0xbe
> [  216.714011]  [<ffffffff8116b29b>] ? __close_fd+0x25/0xdd
> [  216.714013]  [<ffffffff81079a27>] ? __lock_is_held+0x3c/0x57
> [  216.714015]  [<ffffffff811508b2>] vfs_write+0xc0/0x145
> [  216.714017]  [<ffffffff81150fd0>] SyS_write+0x51/0x8f
> [  216.714019]  [<ffffffff8152d097>] system_call_fastpath+0x12/0x6f
> [  216.714063] zram: Removed device: zram0
> 
> 
> 	-ss
>