Hi! > Currently, the PF_FREEZE process flag is used to indicate that the process > should enter the refrigerator as soon as possible. Unfortunately it is set by > the freezer while the process may be changing its flags for another reason > and this may lead to a race between the freezer and the process itself. > > This problem may be solved by introducing an additional member, called (for > example) 'freezing', into task_struct which will only be used to indicate that > the process should enter the refrigerator. Then, if the 'freezing' member of > task_struct is reset by the process itself only after it has entered the > refrigerator, the modifications of it will be guaranteed to occur at different > times, because the freezer can only set it before the process enters the > refrigerator. Thus the code will be SMP-safe even though no explicit locking > is used. I do not think we can go without locking here. > @@ -31,7 +30,7 @@ static inline void freeze(struct task_st > */ > static inline void do_not_freeze(struct task_struct *p) > { > - p->flags &= ~PF_FREEZE; > + p->freezing = 0; > } > > /* > @@ -52,7 +51,8 @@ static inline int thaw_process(struct ta > */ > static inline void frozen_process(struct task_struct *p) > { > - p->flags = (p->flags & ~PF_FREEZE) | PF_FROZEN; > + p->flags |= PF_FROZEN; > + p->freezing = 0; > } Is mb() needed between |= and freezing = 0? > extern void refrigerator(void); > Index: linux-2.6.19-rc6-mm1/include/linux/sched.h > =================================================================== > --- linux-2.6.19-rc6-mm1.orig/include/linux/sched.h > +++ linux-2.6.19-rc6-mm1/include/linux/sched.h > @@ -1065,6 +1065,9 @@ struct task_struct { > #ifdef CONFIG_TASK_DELAY_ACCT > struct task_delay_info *delays; > #endif > +#ifdef CONFIG_PM > + int freezing; /* if set, we should be freezing for suspend */ > +#endif > #ifdef CONFIG_FAULT_INJECTION > int make_it_fail; > #endif It is int, imagine machine that can't do 32-bit atomic access (only does 64 bits). On such beast (alpha? something stranger?) this will clobber make_it_fail field, sometimes. OTOH on i386 normal instructions can be used. But that's okay, we should just use atomic_t here. Should be as fast on i386/x86-64, and still safe. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html