Messages in this thread | | | Date | Sat, 21 Feb 2015 08:42:23 +0100 (CET) | From | Fabian Frederick <> | Subject | Re: [PATCH 6/7 linux-next] wan: cosa: replace current->state by set_current_state() |
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> On 20 February 2015 at 19:58 Peter Zijlstra <peterz@infradead.org> wrote: > > > On Fri, Feb 20, 2015 at 09:34:28PM +0300, Sergei Shtylyov wrote: > > Hello. > > > > On 02/20/2015 09:12 PM, Fabian Frederick wrote: > > > > >Use helper functions to access current->state. > > >Direct assignments are prone to races and therefore buggy. > > > > >current->state = TASK_RUNNING is replaced by __set_current_state() > > > > You sometimes use __set_current_state() and sometimes > >set_current_state(). > > It depends on which state; setting yourself TASK_RUNNING is free of > wakeup races -- you're already running after all, so it can safely use > __set_current_state(). > > Setting a blocking state otoh needs set_current_state() which issues a > full memory barriers with the store (critically in this case, > effectively after the store) such that it orders the state store with a > subsequent load in the condition check if it really needs to go to > sleep. > > > In full: > > current->state = TASK_UNINTERRUPTIBLE; wait = false; > smp_mb(); smp_wmb(); > if (wait) p->state = TASK_RUNNING; > schedule(); > > Without that smp_mb(); the following order is possible: > > if (wait) > wait = false; > smp_wmb(); > p->state = TASK_RUNNING; > current->state = TASK_UNINTERRUPTIBLE; > schedule(); > > And we'll wait forever more.. Do I have to add more comments in changelogs or is it OK for you ? Maybe something like: " current->state = TASK_RUNNING can safely be converted to __set_current_state() as we're already in that state. Other assignments are converted to set_current_state() (which uses set_mb()).
" Regards, Fabian >
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