Re: interrupt checks for spinlocks

[Davide Libenzi <davidel@xmailserver.org>]

On Sun, 3 Nov 2002, William Lee Irwin III wrote:

> On Sun, 3 Nov 2002, William Lee Irwin III wrote:
> [...]
> >> The only action taken is printk() and dump_stack(). No arch code has
> >> been futzed with to provide irq tainting yet. Looks like a good way
> >> to shake out lurking bugs to me (somewhat like may_sleep() etc.).
>
> On Sun, Nov 03, 2002 at 04:15:46PM -0800, Davide Libenzi wrote:
> > Wouldn't it be interesting to keep a ( per task ) list of acquired
> > spinlocks to be able to diagnose cross locks in case of stall ?
> > ( obviously under CONFIG_DEBUG_SPINLOCK )
>
> That would appear to require cycle detection, but it sounds like a
> potential breakthrough usage of graph algorithms in the kernel.
> (I've always been told graph algorithms would come back to haunt me.)
> Or maybe not, deadlock detection has been done before.
>
> A separate patch/feature/whatever for deadlock detection could do that
> nicely, though. What I've presented here is meant only to flag far more
> trivial errors with interrupt enablement/disablement than the full
> deadlock detection problem.

It's not realy a graph Bill.  Each task has a list of acquired locks (
by address ). You keep __LINE__ and __FILE__ with you list items. When
there's a deadlock you'll have somewhere :

   TSK#N	TSK#M
   -------------
   ...		...
   LCK#I	LCK#J
   ...		...
-> LCK#J	LCK#I

Then with a SysReq key you dump the list of acquired locks for each task
who's spinning for a lock. IMO it might be usefull ...



- Davide