On 12/23, Ingo Molnar wrote: > > * Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > Initially I thought that this is obviously wrong, irqsave/irqrestore > > assume that "flags" is owned by the caller, not by the lock. And > > iirc this was certainly wrong in the past. > > > > But when I look at spinlock.c it seems that this code can actually > > work. _irqsave() writes to FLAGS after it takes the lock, and > > _irqrestore() has a copy of FLAGS before it drops this lock. > > I don't think that's true: if it was then the lock would not be > irqsave, a hardware-irq could come in after the lock has been taken > and before flags are saved+disabled. I do agree that this pattern is not safe, that is why I decided to ask. But, unless I missed something, with the current implementation spin_lock_irqsave(lock, global_flags) does: unsigned long local_flags; local_irq_save(local_flags); spin_lock(lock); global_flags = local_flags; so the access to global_flags is actually serialized by lock. > So AFAICS this is an unsafe pattern, beyond being ugly as hell. Yes, I think the same. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
