Messages in this thread | | | From | "Liu, Chuansheng" <> | Subject | RE: [PATCH 1/2] genirq: Fix the possible synchronize_irq() wait-forever | Date | Fri, 21 Feb 2014 11:26:04 +0000 |
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> -----Original Message----- > From: Thomas Gleixner [mailto:tglx@linutronix.de] > Sent: Friday, February 21, 2014 7:11 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 Fri, 21 Feb 2014, Liu, Chuansheng wrote: > > Hello Thomas, > > > > > -----Original Message----- > > > From: Thomas Gleixner [mailto:tglx@linutronix.de] > > > Sent: Friday, February 21, 2014 6:34 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 Fri, 21 Feb 2014, Liu, Chuansheng wrote: > > > > But feels there is another case which the synchronize_irq waited there > > > forever, > > > > it is no waking up action from irq_thread(). > > > > > > > > CPU0 CPU1 > > > > disable_irq() irq_thread() > > > > synchronize_irq() > > > > wait_event() > > > > adding the __wait into the queue wake_threads_waitq > > > > test threads_active==0 > > > > atomic_dec_and_test(threads_active) 1 -- > 0 > > > > > > > waitqueue_active(&desc->wait_for_threads) > > > > <== Here without smp_mb(), > CPU1 > > > maybe detect > > > > the queue is still empty?? > > > > schedule() > > > > > > > > It will cause although the threads_active is 0, but irq_thread() didn't do > the > > > waking up action. > > > > Is it reasonable? Then maybe we can add one smp_mb() before > > > waitqueue_active. > > > > > > I think you have a point there, but not on x86 wherre the atomic_dec > > > and the spinlock on the queueing side are full barriers. For non-x86 > > > there is definitely a potential issue. > > > > > But even on X86, spin_unlock has no full barrier, the following scenario: > > CPU0 CPU1 > > spin_lock > > atomic_dec_and_test > > insert into queue > > spin_unlock > > checking waitqueue_active > > But CPU0 sees the 0, right? Not be clear here:) The atomic_read has no barrier.
Found commit 6cb2a21049b89 has one similar smp_mb() calling before waitqueue_active() on one X86 CPU.
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