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