On 04/03, Srivatsa Vaddagiri wrote: > > On Tue, Apr 03, 2007 at 07:03:36PM +0400, Oleg Nesterov wrote: > > > is better to introduce a new helper for that, kthread_thaw_stop() or > > something. > > Will think of that.
I changed my mind :) The problem is general, I am starting to believe it is better to change kthread_stop(). > > > kthread_stop(p) > > > { > > > int old_exempt_flags; > > > > > > task_lock(p); > > > old_exempt_flags = p->flags; > > > p->flags |= PFE_ALL; /* Exempt 'p' from being frozen? */ > > > > I agree, we should mark this thread as non-freezable, but we can't modify > > p->flags, this is racy. "current" owns its ->flags and it is not atomic. > > Note that thaw_process() checks frozen(p) when it clears PF_FROZEN. > > I suspected that we cannot modify p->flags just like that. How abt > moving freezer exemption bits to a separate field, which is protected by > task_lock? Probably yes... In that case it makes sense to move PF_FREEZER_SKIP/PF_FROZEN to the new field as well. Perhaps we can ignore this problem for now. Freezer is not 100% reliable anyway. For example, worker_thread: for (;;) { try_to_freeze(); prepare_to_wait(); if (...) schedule(); finish_wait(); } This is racy, we can miss freeze_process()->signal_wake_up() if it happens between try_to_freeze() and prepare_to_wait(). We have to check TIF_FREEZE before entering schedule() if we want to fix this race. Should we? I don't know. This will uglify the code, and the probability of this race is very low. Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/