On Sun, 27 Jun 1999, Peter Wemm wrote:
> Matthew Dillon wrote:
> > Ah, yes, some of us were just discussing this in a small mailing list.
> > Hopefully Kirk will pick up on it soon. Ah well.. someone else gets to b
> e
> > the brunt of it for a change :-). Kirk doesn't have an SMP box so he
> > didn't see the bug.
> >
> > I have tentitively tracked the problem down to the apparent inability of
> > lockmgr() locks to function from interrupts, even when used in a
> > non-blocking manner, due to the simplelock's it uses internally. The
> > new buffer cache code Kirk committed switched from B_BUSY (manually
> > implemented locks) to lockmgr() locks. I think what is going on is
> > that mainline code is getting a simplelock and then an interrupt is
> > coming along and also trying to get the same lock, but I can't be sure
> > because my DDB backtraces are somewhat munged.
>
> In this case, it was just a programming error.. The key to remember is that
> the simplelocks are used to protect the state of the complex lock, they are
> not the lock themselves. lockmgr() holds the interlock while gaining or
> removing references etc and then frees the simplelock so that it can sleep
> if required etc. The actual implementation of the simplelock routines
> is interrupt safe (and has to be).
The simple_lock* macros don't seem to use the interrupt safe versions
(ss_lock etc). What happens if an interrupt is recieved after gaining
buftimelock and the interrupt routine also tries to call BUF_LOCK?
--
Doug Rabson Mail: [EMAIL PROTECTED]
Nonlinear Systems Ltd. Phone: +44 181 442 9037
To Unsubscribe: send mail to [EMAIL PROTECTED]
with "unsubscribe freebsd-current" in the body of the message
