Hello Thomas, > -----Original Message----- > From: Thomas Gleixner [mailto:[email protected]] > Sent: Friday, February 21, 2014 6:34 PM > To: Liu, Chuansheng > Cc: [email protected]; 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
Here after inserting into the queue, before waitqueue_active, there is no mb. So is it still the case? Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
