On 02/13, Nicholas Mc Guire wrote: > > On Thu, 12 Feb 2015, Oleg Nesterov wrote: > > > Nicholas, sorry, I sent the patch but forgot to CC you. > > See https://lkml.org/lkml/2015/2/12/587 > > > > And please note that "completion" was specially designed to guarantee > > that complete() can't play with this memory after wait_for_completion/etc > > returns. > > > > hmmm.... I guess that "falling out of context" can happen in a number of cases > with completion - any of the timeout/interruptible variants e.g: > > void xxx(void) > { > struct completion c; > > init_completion(&c); > > expose_this_completion(&c); > > wait_for_completion_timeout(&c,A_FEW_JIFFIES); > } > > and if the other side did not call complete() within A_FEW_JIFFIES then > it would result in the same failure - I don't think the API can prevent > this type of bug.
Yes sure, but in this case the user of wait_for_completion_timeout() should blame itself, it is simply buggy. > Tt has to be ensured by additional locking Yes, but > drivers/misc/tifm_7xx1.c:tifm_7xx1_resume() resolve this issue by resetting > the completion to NULL and testing for !NULL before calling complete() > with appropriate locking protection access. I don't understand this code, I can be easily wrong. but at first glance it doesn't need completion at all. Exactly because it relies on the additional fm->lock. ->finish_me could be "task_struct *", the tifm_7xx1_resume() could simply do schedule_timeout(), tifm_7xx1_isr() could do wake_up_process(). Nevermind, this is off-topic and most probably I misread this code. > Never the less of course the proposed change in completion_done() was a bug - > many thanks for catching that so quickly ! OK, perhaps you can ack the fix I sent? Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
