RE: [PATCH 1/2] genirq: Fix the possible synchronize_irq() wait-forever

[Liu, Chuansheng]

Hello Thomas,

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@xxxxxxxxxxxxx]
> Sent: Monday, February 10, 2014 4:58 PM
> To: Liu, Chuansheng
> Cc: linux-kernel@xxxxxxxxxxxxxxx; Wang, Xiaoming
> Subject: Re: [PATCH 1/2] genirq: Fix the possible synchronize_irq() wait-forever
> 
> On Mon, 10 Feb 2014, Chuansheng Liu wrote:
> > There is below race between irq handler and irq thread:
> > irq handler                             irq thread
> >
> > irq_wake_thread()                       irq_thread()
> >   set bit RUNTHREAD
> >   ...                                    clear bit RUNTHREAD
> >                                          thread_fn()
> >                                          [A]test_and_decrease
> >                                                thread_active
> >   [B]increase thread_active
> >
> > If action A is before action B, after that the thread_active
> > will be always > 0, and for synchronize_irq() calling, which
> > will be waiting there forever.
> 
> No. thread_active is 0, simply because after the atomic_dec_and_test()
> it is -1 and the atomic_inc on the other side will bring it back to 0.
> 
Yes, you are right. The thread_active is back to 0 at last.

The case we meet is:
1/ T1: blocking at disable_irq() -- > sync_irq() -- > wait_event()
[  142.678681]  [<c1a5b353>] schedule+0x23/0x60
[  142.683466]  [<c12b24c5>] synchronize_irq+0x75/0xb0
[  142.688931]  [<c125fad0>] ? wake_up_bit+0x30/0x30
[  142.694201]  [<c12b33ab>] disable_irq+0x1b/0x20
[  142.699278]  [<c17a79bc>] smb347_shutdown+0x2c/0x50
[  142.704744]  [<c1789f7d>] i2c_device_shutdown+0x2d/0x40
[  142.710597]  [<c1601734>] device_shutdown+0x14/0x140
[  142.716161]  [<c12535f2>] kernel_restart_prepare+0x32/0x40
[  142.722307]  [<c1253613>] kernel_restart+0x13/0x60

2/ The corresponding irq thread is at sleep state:
[  587.552408] irq/388-SMB0349 S f1c47620  7276   119      2 0x00000000
[  587.552439]  f1d6bf20 00000046 f1c47a48 f1c47620 f1d6bec4 9e91731c 00000001 c1a5f3a5
[  587.552468]  c20469c0 00000001 c20469c0 f36559c0 f1c47620 f307bde0 c20469c0 f1d6bef0
[  587.552497]  00000296 00000000 00000296 f1d6bef0 c1a5bfa6 f1c47620 f1d6bf14 c126e329
[  587.552501] Call Trace:
[  587.552519]  [<c1a5f3a5>] ? sub_preempt_count+0x55/0xe0
[  587.552535]  [<c1a5bfa6>] ? _raw_spin_unlock_irqrestore+0x26/0x50
[  587.552548]  [<c126e329>] ? set_cpus_allowed_ptr+0x59/0xe0
[  587.552563]  [<c1a5b093>] schedule+0x23/0x60
[  587.552576]  [<c12b2ae1>] irq_thread+0xa1/0x130
[  587.552588]  [<c12b27f0>] ? irq_thread_dtor+0xa0/0xa0

3/ All the cpus are in the idle task;

So we guess the thread_active is not 0 at that time, but irq thread is doing nothing at that time.
Thought for a long time, but there is no idea, and it is just hit once.

Appreciated if you have some idea, thanks.



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