* Ingo Molnar <[email protected]> wrote:
> no. Write-locks are unfair too, and there's no guarantee that writes
> are listened to. That's why nested read_lock() is valid, while nested
> down_read() is invalid.
>
> Take a look at arch/i386/kernel/semaphore.c, __write_lock_failed()
> just adds back the RW_LOCK_BIAS and retries in a loop. There's no
> difference to an open-coded write_trylock loop - unless i'm missing
> something fundamental.
did i ever mention that i find rwlocks evil, inefficient and bug-prone,
and that we should get rid of them? :-)
(Most rwlock users can be converted to straight spinlocks just fine, but
there are a couple of places that rely on read-lock nesting. The
hardest-to-fix offenders are nested rcu_read_locks() in the netfilter
code. I gave up converting them to saner locking, PREEMPT_RCU works it
around in the -rt tree, by not being rwlock based.)
Ingo
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