Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [CHECKER] a couple potential deadlocks in 2.4.5-ac8 | Date | Sun, 10 Jun 2001 21:53:24 +1000 |
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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? > > A B > read_lock() > write_lock() > ...sleeps... > read_lock() > ...sleeps... > > 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).
Also, netfilter will break (brlocks inherit this property from their spinlocks constituents).
Rusty. [1] Well, we could, but we'd have to do a special "same CPU?" check, which would suck badly. -- Premature optmztion is rt of all evl. --DK - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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