Re: [patch] increase spinlock-debug looping timeouts from 1 sec to 1 min

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> 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