On 3/5/07, Simon Arlott <[EMAIL PROTECTED]> wrote:
On Mon, March 5, 2007 11:19, Johannes Stezenbach wrote:
> On Mon, Mar 05, 2007 at 01:58:14AM +0100, Oliver Endriss wrote:
>> Simon Arlott wrote:
>> > Is any part of the patch going to be applied? I mentioned this
>> > problem in September last year and it looks like it's existed for
>> > years (the semaphore locking did the same thing).
>>
>> Well, I hoped that someone more familiar with the demuxer stuff would
>> comment on the patch. I am not very happy about using non-interruptible
>> lock operations...
Why? If there are deadlocks these should be fixed, not ignored.
>> Anyway, I'll apply the patch to HG master if you submit an updated patch:
>> - Please add a line of comment to each mutex_lock() stating _why_ the
>> non-interruptible lock has to be used at this place.
What's the point of doing that?
> IMHO using mutex_lock_interruptible() is almost always wrong.
>
> The only use it has in dvb-core is to recover from locking bugs --
> if it deadlocks you can Ctrl-C out of it
> (instead of being left with a non-killable program -> reboot).
This is what lockdep is for.
just as a small note here, lockdep doesn't support mutex/semaphore
based lockups. I figured out such a bug in the pcmcia subsystem when
ejecting a device with pccardctl eject;
[process1 semaphore got locked] - in the pcmcia framework
[process2 mutex got locked] - in the sysfs framework
[process1 trying to lock mutex]
[process2 trying to lock semaphore]
so I wouldn't always rely on lockdep at the moment.
> But with mutex_lock_interruptible() it's easy to introduce
> signal handling bugs, which Simon confirmed to exist.
It's also easy to find examples of people needing to rmmod/modprobe because
dvr0 started returning -EBUSY on
open() after they closed something.
> Fixing those up without reverting to mutex_lock() way might
> be possible, but is more difficult.
It'd introduce lot of unneccessary -ERESTARTSYS, just to avoid the
possiblity of waiting on mutex_lock for a
few msecs.
--
Simon Arlott
_______________________________________________
linux-dvb mailing list
[email protected]
http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
--
Markus Rechberger
_______________________________________________
linux-dvb mailing list
[email protected]
http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
