In article <19317.992115181@redhat.com>,
David Woodhouse <dwmw2@infradead.org> wrote:
>
>Obtaining a read lock twice can deadlock too, can't it?
If it does (with spinlocks), then that's an implementation bug (which
might well be there). We depend on the read-lock being recursive in a
lot of places, notably the fact that we don't disable interrupts while
holding read-locks if we know that the interrupt routines only take a
read-lock.
> A B
> read_lock()
> write_lock()
> ...sleeps...
> read_lock()
> ...sleeps...
>
>Or do we not make new readers sleep if there's a writer waiting?
The writer-waiter should not be spinning with the write lock held.
Note that the blocking versions are different, and I explicitly meant
only the read-spinlocks, not read-semaphores. For the semaphores I think
your schenario is indeed correct.
Linus
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This archive was generated by hypermail 2b29 : Fri Jun 15 2001 - 21:00:11 EST