On Tue, 2012-10-30 at 14:45 -0400, Steven Rostedt wrote: > On Wed, 2012-10-31 at 03:33 +0900, anish kumar wrote: > > > > CPU 0 CPU 1 > > > > > > data = something flags = IRQ_WORK_BUSY > > > smp_mb() (implicit with cmpxchg smp_mb() > > > on flags in claim) execute_work (sees data from CPU > > > 0) > > > try to claim > > > > > As I understand without the memory barrier proposed by you the situation > > would be as below: > > CPU 0 CPU 1 > > > > data = something flags = IRQ_WORK_BUSY > > smp_mb() (implicit with cmpxchg execute_work (sees data from CPU 0) > > on flags in claim) > > _success_ in claiming and goes > > Correct, because it would see the stale value of flags. > > > ahead and execute the work(wrong?) > > cmpxchg cause flag to IRQ_WORK_BUSY > > > > Now knows the flag==IRQ_WORK_BUSY > > > > Am I right? > > right. > > > > > Probably a stupid question.Why do we return the bool from irq_work_queue > > when no one bothers to check the return value?Wouldn't it be better if > > this function is void as used by the users of this function or am I > > looking at the wrong code. > > Not a stupid question, as I was asking that to myself just earlier > today. But forgot to mention it as well. Especially, because it makes it > look like there's a bug in the code. Maybe someday someone will care if > their work was finished by itself, or some other CPU. > > Probably should just nix the return value. Can I send a patch to fix this? > > -- Steve > >
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