Re: [PATCH][RFC]: mutex: adaptive spin

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Tue, 6 Jan 2009, Linus Torvalds wrote:
> > 
> > Right now, if some process deadlocks on a mutex, we get hung process, 
> > but with a nice backtrace and hopefully other things (that don't need 
> > that lock) still continue to work.
> 
> Clarification: the "nice backtrace" we only get with something like 
> sysrq-W, of course. We don't get a backtrace _automatically_, but with 
> an otherwise live machine, there's a better chance that people do get 
> wchan or other info. IOW, it's at least a fairly debuggable situation.

btw., the softlockup watchdog detects non-progressing uninterruptible 
tasks (regardless of whether they locked up due to mutexes or any other 
reason).

This does occasionally help in debugging deadlocks:

  http://marc.info/?l=linux-mm&m=122889587725061&w=2

but it would indeed be also good to have the most common self-deadlock 
case checked unconditionally in the mutex slowpath.

	Ingo
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