On Sun, 7 Jul 2002, Zwane Mwaikambo wrote:
> Hi Bart, Martin
> I'm seeing a number of deadlocks, most of them due to ide__sti
> enabling interrupts in a critical section which needs to be protected
> against interrupts too.
I'm seeing blue sky ;-)
Which IDE patch?
> Another dangerous scenario is the following, from here the usage of
> ide__sti becomes questionable.
>
> queue_commands() {
> ide__sti();
> start_request();
> }
> ...
> start_request() {
> spin_unlock_irq();
> frob_ide();
Whats that?
> spin_lock_irq();
> }
>
> and also;
>
> if (ch->unmask)
> ide__sti(); /* local CPU only */
>
> /* service this interrupt, may set handler for next interrupt */
> startstop = handler(drive, drive->rq);
> spin_lock_irq(ch->lock);
>
> If someone can explain to me what ide__sti really is trying to achieve
> i'd greatly appreciate it.
ide_sti() its just __sti() (except atari).
Note that ide_do_request() is called under spin_lock_irqsave(ch->lock,
flags). We have to unlock or we will get deadlock - imagine we are holding
lock and we get irq (shared irq, unexpected one) and we try to lock in
ata_irq_request() -> deadlock.
Also for most code in start_request() we dont need lock, we need it only
for calling block layer helpers, changing/reading IDE_BUSY bit and
ch->handler, timer and drive->rq.
Also we cannot disable interrupts, because we wont know when drive is
interrupting us, missed irqs.
Please also read my previous mails to Alex...
Regards
-- Bartlomiej> Regards, > Zwane Mwaikambo > > -- > function.linuxpower.ca >
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This archive was generated by hypermail 2b29 : Sun Jul 07 2002 - 22:00:18 EST