Re: panic: mutex Giant not owned

On Thursday 25 March 2004 07:53 pm, Bruce Evans wrote:
> On Thu, 25 Mar 2004, John Baldwin wrote:
> > On Thursday 25 March 2004 05:39 am, Lukas Ertl wrote:
> > > Hi,
> > >
> > > I was dropped into DDB after a panic and tried to save a coredump with
> > > "call doadump", which resulted in a:
> > >
> > > panic: mutex Giant not owned in /usr/src/sys/cam/cam_xpt.c:3970
> > >
> > > Second call to "doadump" succeeded, but savecore(8) couldn't save the
> > > core ('bad dump header' or something like this).
> >
> > Cute.  I should fix mtx_assert() to just bail and not panic if panicstr
> > is already set.
>
> Er, the panic is correct.  Panic dump code must not use normal locking,
> since then it won't work if it hits an unlockable lock.  panic() usually
> recursively panics earlier, near the sync() in boot(), if it hits an
> unlocakable lock.  Changing mtx_assert() to not panic if panicstr is
> set would be worse for this than for the panic dump part, since sync()
> is normal file system code that depends on normal locking for correctness.

I misread it at first.  mtx_assert() already doesn't recursively panic.  The 
current behavior does seem correct though annoying since you can't just take 
an arbitrary dump it seems.

-- 
John Baldwin <jhb_at_FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org