Messages in this thread | | | From | "Liu, Chuansheng" <> | Subject | RE: [PATCH 1/2] genirq: Fix the possible synchronize_irq() wait-forever | Date | Thu, 20 Feb 2014 00:34:51 +0000 |
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Hello Thomas,
> -----Original Message----- > From: Thomas Gleixner [mailto:tglx@linutronix.de] > Sent: Monday, February 10, 2014 4:58 PM > To: Liu, Chuansheng > Cc: linux-kernel@vger.kernel.org; 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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