Hello Thomas, > -----Original Message----- > From: Thomas Gleixner [mailto:t...@linutronix.de] > Sent: Friday, February 21, 2014 7:53 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: > > > > > 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. > > Indeed, you are completely right. Great detective work! Thanks your encouraging.
> > I'm inclined to remove the waitqueue_active() alltogether. It's > creating more headache than it's worth. If I am understanding well, removing the checking of waitqueue_active(), and call wakeup() directly which will check list with spinlock protection. If so, I can prepare one patch for it:) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/