Date:	Sun, 27 Sep 2015 10:41:39 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sedat Dilek <sedat.dilek@...il.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL rcu/urgent] Fix two more 4.3 regressions

On Sun, Sep 27, 2015 at 07:24:22PM +0200, Sedat Dilek wrote:
> On Sun, Sep 27, 2015 at 6:42 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > On Sun, Sep 27, 2015 at 05:55:43PM +0200, Sedat Dilek wrote:
> >> On Sun, Sep 27, 2015 at 5:49 PM, Paul E. McKenney
> >> <paulmck@...ux.vnet.ibm.com> wrote:
> >> > On Sun, Sep 27, 2015 at 09:37:05AM +0200, Sedat Dilek wrote:
> >> >> On Sun, Sep 27, 2015 at 9:32 AM, Paul E. McKenney
> >> >> <paulmck@...ux.vnet.ibm.com> wrote:
> >> >> > On Sun, Sep 27, 2015 at 08:28:39AM +0200, Sedat Dilek wrote:
> >
> > [ . . . ]
> >
> >> Hi Paul :-),
> >>
> >> Here is the stack trace.
> >>
> >> [   23.045871] BUG: sleeping function called from invalid context at
> >> kernel/workqueue.c:2678
> >> [   23.045982] in_atomic(): 0, irqs_disabled(): 1, pid: 1399, name: acpid
> >> [   23.046064] 3 locks held by acpid/1399:
> >> [   23.046066]  #0:  (&evdev->mutex){+.+...}, at: [<ffffffff8174ac7c>]
> >> evdev_release+0xbc/0xf0
> >> [   23.046081]  #1:  (&dev->mutex#2){+.+...}, at: [<ffffffff81742397>]
> >> input_close_device+0x27/0x70
> >> [   23.046093]  #2:  (hid_open_mut){+.+...}, at: [<ffffffffa0056388>]
> >> usbhid_close+0x28/0xb0 [usbhid]
> >> [   23.046106] irq event stamp: 3306
> >> [   23.046109] hardirqs last  enabled at (3305): [<ffffffff8192ae32>]
> >> _raw_spin_unlock_irq+0x32/0x60
> >> [   23.046115] hardirqs last disabled at (3306): [<ffffffff81121017>]
> >> del_timer_sync+0x37/0x110
> >> [   23.046122] softirqs last  enabled at (2704): [<ffffffff818b12c9>]
> >> local_bh_enable+0x9/0x20
> >> [   23.046128] softirqs last disabled at (2702): [<ffffffff818b12a9>]
> >> local_bh_disable+0x9/0x20
> >> [   23.046136] CPU: 2 PID: 1399 Comm: acpid Not tainted
> >> 4.3.0-rc3-3-llvmlinux-amd64 #1
> >> [   23.046139] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
> >> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
> >> [   23.046143]  ffff8800d36ee948 0000000000000092 0000000000000000
> >> ffff8800bbacfae8
> >> [   23.046151]  ffffffff8149adad ffff8800bbacfb18 ffffffff810cd1ea
> >> ffffffff81c56f0a
> >> [   23.046158]  ffff8800c22dc400 0000000000000000 0000000000000a76
> >> ffff8800bbacfb58
> >> [   23.046165] Call Trace:
> >> [   23.046172]  [<ffffffff8149adad>] dump_stack+0x7d/0xa0
> >> [   23.046177]  [<ffffffff810cd1ea>] ___might_sleep+0x28a/0x2a0
> >> [   23.046182]  [<ffffffff810cceef>] __might_sleep+0x4f/0xc0
> >> [   23.046187]  [<ffffffff810afbff>] start_flush_work+0x2f/0x290
> >> [   23.046192]  [<ffffffff810afbac>] flush_work+0x5c/0x80
> >> [   23.046195]  [<ffffffff810afb6a>] ? flush_work+0x1a/0x80
> >> [   23.046202]  [<ffffffff810eed0d>] ? trace_hardirqs_off+0xd/0x10
> >> [   23.046206]  [<ffffffff810aecc8>] ? try_to_grab_pending+0x48/0x360
> >> [   23.046211]  [<ffffffff8192ac53>] ? _raw_spin_lock_irqsave+0x73/0x80
> >> [   23.046216]  [<ffffffff810afff9>] __cancel_work_timer+0x179/0x260
> >> [   23.046221]  [<ffffffff8192add2>] ? _raw_spin_unlock_irqrestore+0x52/0x80
> >> [   23.046226]  [<ffffffff81120fcd>] ? try_to_del_timer_sync+0xad/0xc0
> >> [   23.046230]  [<ffffffff810afe78>] cancel_work_sync+0x18/0x20
> >> [   23.046237]  [<ffffffffa00563d5>] usbhid_close+0x75/0xb0 [usbhid]
> >> [   23.046245]  [<ffffffffa00394d1>] hidinput_close+0x31/0x40 [hid]
> >> [   23.046251]  [<ffffffffa00394a0>] ? hidinput_open+0x40/0x40 [hid]
> >> [   23.046256]  [<ffffffff817423b8>] input_close_device+0x48/0x70
> >> [   23.046261]  [<ffffffff8174ac96>] evdev_release+0xd6/0xf0
> >> [   23.046267]  [<ffffffff812728c7>] __fput+0x107/0x240
> >> [   23.046271]  [<ffffffff81272756>] ____fput+0x16/0x20
> >> [   23.046276]  [<ffffffff810b945c>] task_work_run+0x6c/0xe0
> >> [   23.046282]  [<ffffffff81003aa7>] prepare_exit_to_usermode+0x117/0x120
> >> [   23.046287]  [<ffffffff81003ce1>] syscall_return_slowpath+0x231/0x2a0
> >> [   23.046292]  [<ffffffff8126efa5>] ? filp_close+0x65/0x90
> >> [   23.046298]  [<ffffffff810ef1c9>] ? trace_hardirqs_on_caller+0x19/0x290
> >> [   23.046303]  [<ffffffff81003017>] ? trace_hardirqs_on_thunk+0x17/0x19
> >> [   23.046308]  [<ffffffff8192bb62>] int_ret_from_sys_call+0x25/0x9f
> >>
> >> Can you give help on how to "debug" this?
> >>
> >> I switched from full-dynticks to simple cpu-accounting which did not help.
> >> But this was only a suspicion as Jiri pointed to the possibility
> >> del_timer_sync() could have get some mis-optimization.
> >>
> >> So, more empty head here.
> >
> > I am not familiar with the "hardirqs last  enabled" debug output, but
> > I am guessing that hardirqs are disabled because  the "last disabled"
> > number is greater than the "last  enabled" number.  So if I understand
> > correctly, something somewhere up the call stack has irqs disabled,
> > but is calling a function that needs them enabled.
> >
> > A quick look at usbhid_close() shows no problem, but then again, I am
> > looking at the v4.2 version rather than whatever you are testing.
> > But v4.3-rc2 looks the same.
> >
> > Looks like you are already in contact with Jiri, which is good.
> >
> > Another thing to try would be to insert might_sleep() calls, after
> > usbhid_close(), since it enables irqs explicitly, but before the call
> > to flush_work().  Jiri's comment can be interpreted as a suggestion
> > to insert a might_sleep() in try_to_del_timer_sync(), though
> > __cancel_work_timer() wouldn't be a bad place to try as well,
> > just before its call to flush_work().
> 
> With...
> 
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1026,6 +1026,8 @@ int try_to_del_timer_sync(struct timer_list *timer)
>         unsigned long flags;
>         int ret = -1;
> 
> +       might_sleep();
> +
>         debug_assert_init(timer);
> 
>         base = lock_timer_base(timer, &flags);
> 
> ...I get now...
> 
> [   53.104411] BUG: sleeping function called from invalid context at
> kernel/time/timer.c:1029
> [   53.104417] in_atomic(): 0, irqs_disabled(): 1, pid: 2100, name: fusermount
> [   53.104419] 1 lock held by fusermount/2100:
> [   53.104420]  #0:  (&type->s_umount_key#33){+.+...}, at:
> [<ffffffff812746ab>] deactivate_super+0x5b/0x70
> [   53.104432] irq event stamp: 3734
> [   53.104433] hardirqs last  enabled at (3733): [<ffffffff810aefb8>]
> mod_delayed_work_on+0x78/0xa0
> [   53.104438] hardirqs last disabled at (3734): [<ffffffff810b045f>]
> flush_delayed_work+0x1f/0x70
> [   53.104441] softirqs last  enabled at (3730): [<ffffffff81204997>]
> wb_shutdown+0x47/0xb0
> [   53.104444] softirqs last disabled at (3728): [<ffffffff81204976>]
> wb_shutdown+0x26/0xb0
> [   53.104449] CPU: 3 PID: 2100 Comm: fusermount Not tainted
> 4.3.0-rc3-4-llvmlinux-amd64 #2
> [   53.104451] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
> [   53.104453]  000000000000000a 0000000000000096 0000000000000000
> ffff8800af39bb28
> [   53.104457]  ffffffff8149cadd ffff8800af39bb58 ffffffff810cd5aa
> ffffffff81c5f2e8
> [   53.104461]  ffff8800c5785940 0000000000000000 0000000000000405
> ffff8800af39bb98
> [   53.104465] Call Trace:
> [   53.104470]  [<ffffffff8149cadd>] dump_stack+0x7d/0xa0
> [   53.104473]  [<ffffffff810cd5aa>] ___might_sleep+0x28a/0x2a0
> [   53.104475]  [<ffffffff810cd2af>] __might_sleep+0x4f/0xc0
> [   53.104480]  [<ffffffff81122055>] try_to_del_timer_sync+0x25/0xe0
> [   53.104483]  [<ffffffff81122204>] del_timer_sync+0xf4/0x110
> [   53.104486]  [<ffffffff8112214b>] ? del_timer_sync+0x3b/0x110
> [   53.104497]  [<ffffffff810b0468>] flush_delayed_work+0x28/0x70
> [   53.104499]  [<ffffffff812049cb>] wb_shutdown+0x7b/0xb0
> [   53.104501]  [<ffffffff812046fd>] bdi_destroy+0x7d/0x2d0
> [   53.104505]  [<ffffffff810efe2d>] ? trace_hardirqs_on+0xd/0x10
> [   53.104509]  [<ffffffff813b7b08>] fuse_put_super+0xf8/0x140
> [   53.104511]  [<ffffffff813b7a10>] ? fuse_evict_inode+0x80/0x80
> [   53.104513]  [<ffffffff81274778>] generic_shutdown_super+0x68/0x120
> [   53.104515]  [<ffffffff81275a80>] kill_anon_super+0x20/0x70
> [   53.104518]  [<ffffffff813b6fcd>] fuse_kill_sb_anon+0x4d/0x60
> [   53.104520]  [<ffffffff812745dd>] deactivate_locked_super+0x4d/0xc0
> [   53.104522]  [<ffffffff812746b3>] deactivate_super+0x63/0x70
> [   53.104525]  [<ffffffff8129fa02>] cleanup_mnt+0xb2/0x140
> [   53.104528]  [<ffffffff8129f93a>] __cleanup_mnt+0x1a/0x30
> [   53.104531]  [<ffffffff810b97bc>] task_work_run+0x6c/0xe0
> [   53.104534]  [<ffffffff81003b8a>] prepare_exit_to_usermode+0x13a/0x140
> [   53.104537]  [<ffffffff81003e11>] syscall_return_slowpath+0x281/0x2f0
> [   53.104540]  [<ffffffff8129c121>] ? SyS_umount+0x341/0x620
> [   53.104542]  [<ffffffff810f02d9>] ? trace_hardirqs_on_caller+0x19/0x290
> [   53.104545]  [<ffffffff81003017>] ? trace_hardirqs_on_thunk+0x17/0x19
> [   53.104550]  [<ffffffff8192da22>] int_ret_from_sys_call+0x25/0x9f
> 
> A problem in fuse?

Or there is a need to qualify might_sleep() by its caller.  So perhaps
set a per-CPU variable in the caller and only call might_sleep() if that
per-CPU variable is set.  Of course, have the caller clear it on return.

							Thanx, Paul

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