Date:	Fri, 26 Dec 2014 18:38:49 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Leon Ma <xindong.ma@...el.com>, Al Viro <viro@...IV.linux.org.uk>
Cc:	akpm@...ux-foundation.org, mhocko@...e.cz, mingo@...nel.org,
	peterz@...radead.org, riel@...hat.com, ionut.m.alexa@...il.com,
	peter@...leysoftware.com, linux-kernel@...r.kernel.org,
	di.zhang@...el.com, zhonghua.sun@...el.com
Subject: Re: [PATCH] move exit_task_work() before exit_fs().

On 12/26, Leon Ma wrote:
>
> We encountered following panic. The scenario is the process is exiting and executing its
> task work. When closing dev node, the driver triggers a firmware reload according to device
> status. Because task->fs is set to NULL in exit_fs(), panic happens.

I think this should be fixed somewhere else...

> Task work is a common interface, we should not limite the resource the user will utilize.

Exactly. And note that with this patch exit_mm()..disassociate_ctty() paths
can't use task works.

Not to mention that this patch moves exit_files() up, even before exit_mm(),
without any explanation.

Add Al. May be we can move exit_fs() down after exit_task_work(), I dunno,
but to me it would be better to change the driver.


> [  118.521972] task: ffff880038de5cd0 ti: ffff880038e86000 task.ti: ffff880038e86000
> [  118.521977] RIP: 0010:[<ffffffff8217a0a6>]  [<ffffffff8217a0a6>] path_init+0x336/0x440
> [  118.521986] RSP: 0000:ffff880038e876a0  EFLAGS: 00010246
> [  118.521991] RAX: 0000000000000000 RBX: ffff880038e87790 RCX: 0000000000000071
> [  118.521996] RDX: ffff88003f30f5d4 RSI: ffffffff82179f75 RDI: ffffffff8209b167
> [  118.522000] RBP: ffff880038e876e0 R08: ffff880038e87730 R09: ffff8800218b44c0
> [  118.522005] R10: 0000000000000000 R11: 000000000000000f R12: ffff880038ebf000
> [  118.522010] R13: ffff880038e87870 R14: ffff880038e87850 R15: 00000000ffffff9c
> [  118.522015] FS:  0000000000000000(0000) GS:ffff88003f300000(0000) knlGS:0000000000000000
> [  118.522020] CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
> [  118.522025] CR2: 0000000000000020 CR3: 0000000039d4f000 CR4: 00000000001007e0
> [  118.522030] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  118.522035] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [  118.522039] Stack:
> [  118.522043]  ffff880038dbc300 ffff880038e876b8 ffffffff822cf046 ffff88002e434f00
> [  118.522056]  ffff880038e87790 ffff880038e87870 ffff880038e87850 00000000ffffff9c
> [  118.522069]  ffff880038e87780 ffffffff8217d419 ffff88003b1de480 ffff88003bbf7700
> [  118.522082] Call Trace:
> [  118.522092]  [<ffffffff822cf046>] ? security_file_alloc+0x16/0x20
> [  118.522100]  [<ffffffff8217d419>] path_openat+0x69/0x4b0
> [  118.522109]  [<ffffffff826b5c7f>] ? is_connected_output_ep+0x15f/0x260
> [  118.522117]  [<ffffffff8217dae9>] do_filp_open+0x39/0x90
> [  118.522125]  [<ffffffff823316ca>] ? string.isra.3+0x3a/0xe0
> [  118.522133]  [<ffffffff82332809>] ? vsnprintf+0x209/0x620
> [  118.522141]  [<ffffffff8216ced2>] file_open_name+0xb2/0xf0
> [  118.522148]  [<ffffffff8216cf46>] filp_open+0x36/0x40
> [  118.522157]  [<ffffffff82404441>] _request_firmware+0x351/0x9c0
> [  118.522164]  [<ffffffff82404b26>] request_firmware+0x16/0x20
> [  118.522172]  [<ffffffff826dd733>] sst_request_fw+0x63/0x510
> [  118.522180]  [<ffffffff8283be10>] ? __mutex_lock_slowpath+0x280/0x3b0
> [  118.522188]  [<ffffffff826df047>] sst_load_fw+0x1f7/0x4a0
> [  118.522195]  [<ffffffff826da81f>] sst_download_fw+0xf/0x60
> [  118.522202]  [<ffffffff826db022>] intel_sst_check_device+0x92/0x1f0
> [  118.522209]  [<ffffffff826db4bd>] sst_set_generic_params+0x18d/0x500
> [  118.522218]  [<ffffffff826cee25>] sst_fill_and_send_cmd.constprop.7+0x95/0x130
> [  118.522226]  [<ffffffff826cf1dd>] sst_send_gain_cmd+0x9d/0xe0
> [  118.522233]  [<ffffffff826cf283>] sst_set_pipe_gain+0x63/0xa0
> [  118.522241]  [<ffffffff826d0665>] sst_send_pipe_gains+0xd5/0x2b0
> [  118.522248]  [<ffffffff826cb5d6>] sst_media_digital_mute+0x46/0x80
> [  118.522257]  [<ffffffff826ab5b1>] snd_soc_dai_digital_mute+0x21/0x60
> [  118.522265]  [<ffffffff826bc39d>] soc_pcm_close+0xbd/0x250
> [  118.522272]  [<ffffffff826bdf2a>] dpcm_fe_dai_close+0x7a/0x150
> [  118.522281]  [<ffffffff8267f138>] snd_pcm_release_substream+0x58/0xb0
> [  118.522289]  [<ffffffff8267f1cf>] snd_pcm_release+0x3f/0xa0//////////
> [  118.522296]  [<ffffffff8216f600>] __fput+0xf0/0x240
> [  118.522304]  [<ffffffff8216f75e>] ____fput+0xe/0x10
> [  118.522312]  [<ffffffff82090195>] task_work_run+0xa5/0xd0
> [  118.522320]  [<ffffffff82072a08>] do_exit+0x2b8/0xad0
> [  118.522327]  [<ffffffff8283d3bf>] ? __schedule+0x3df/0x820
> [  118.522335]  [<ffffffff820733af>] do_group_exit+0x3f/0xa0
> [  118.522343]  [<ffffffff82082b6e>] get_signal_to_deliver+0x24e/0x650
> [  118.522352]  [<ffffffff8200232d>] do_signal+0x4d/0x960
> [  118.522360]  [<ffffffff82097584>] ? hrtimer_start_range_ns+0x14/0x20
> [  118.522368]  [<ffffffff8262a98d>] ? binder_ioctl+0x15d/0x990
> [  118.522377]  [<ffffffff82002ca5>] do_notify_resume+0x65/0x80
> [  118.522384]  [<ffffffff82844efa>] int_signal+0x12/0x17
> 
> Signed-off-by: Leon Ma <xindong.ma@...el.com>
> Signed-off-by: Zhang Di <di.zhang@...el.com>
> Signed-off-by: Sun Zhonghua <zhonghua.sun@...el.com>
> ---
>  kernel/exit.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 1ea4369..64ba13b 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -729,6 +729,8 @@ void do_exit(long code)
>  	tsk->exit_code = code;
>  	taskstats_exit(tsk, group_dead);
>  
> +	exit_files(tsk);
> +	exit_task_work(tsk);
>  	exit_mm(tsk);
>  
>  	if (group_dead)
> @@ -737,12 +739,10 @@ void do_exit(long code)
>  
>  	exit_sem(tsk);
>  	exit_shm(tsk);
> -	exit_files(tsk);
>  	exit_fs(tsk);
>  	if (group_dead)
>  		disassociate_ctty(1);
>  	exit_task_namespaces(tsk);
> -	exit_task_work(tsk);
>  	exit_thread();
>  
>  	/*
> -- 
> 1.7.9.5
> 

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