linux-kernel - Re: qrwlock && read-after-read

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Date:	Tue, 4 Aug 2015 19:32:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <Waiman.Long@...com>, linux-kernel@...r.kernel.org
Subject: Re: qrwlock && read-after-read

On Tue, Aug 04, 2015 at 03:40:43PM +0200, Oleg Nesterov wrote:
> Lets fix the lockdep annotaions?
> 
> Oleg.
> 
> --- x/include/linux/rwlock_api_smp.h
> +++ x/include/linux/rwlock_api_smp.h
> @@ -146,7 +146,7 @@ static inline int __raw_write_trylock(rw
>  static inline void __raw_read_lock(rwlock_t *lock)
>  {
>  	preempt_disable();
> -	rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
> +	lock_acquire(..., /* read */ in_interrupt() 2 : 1, ...);
>  	LOCK_CONTENDED(lock, do_raw_read_trylock, do_raw_read_lock);
>  }

I think that suffers the same problems we had before; see:

  8acd91e86208 ("locking/lockdep: Revert qrwlock recusive stuff")
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