Re: [CHECKER] a couple potential deadlocks in 2.4.5-ac8

David Woodhouse
2001-06-10T12:00:47Z

rusty@rustcorp.com.au said:
> In message <19317.992115181@redhat.com> you write:
> > torvalds@transmeta.com said:
> > > Good point. Spinlocks (with the exception of read-read locks, of
> > > course) and semaphores will deadlock on recursive use, while the BKL
> > > has this "process usage counter" recursion protection.
> >
> > Obtaining a read lock twice can deadlock too, can't it
> > Or do we not make new readers sleep if there's a writer waiting?
>
> We can never[1] make new readers sleep if there's a writer waiting, as
> Linus guaranteed that an IRQ handler which only ever grabs a read lock
> means the rest of the code doesn't need to block interrupts on its
> read locks (see Documentation/spinlock.txt IIRC).

You're right. Despite the fact that upon closer examination it's obvious
that Linus was only referring to rw-spinlocks as safe, I was actually
thinking of rw-semaphores.

--
dwmw2