linux-kernel - Re: [PATCH] m32r: Revise __raw_read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 24 Sep 2006 00:20:36 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Hirokazu Takata <takata@...ux-m32r.org>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m32r: Revise __raw_read_trylock()

On Fri, Sep 22, 2006 at 03:29:53PM +0900, Hirokazu Takata wrote:
>  
> -#define __raw_read_trylock(lock) generic__raw_read_trylock(lock)
> +static inline int __raw_read_trylock(raw_rwlock_t *lock)
> +{
> +	atomic_t *count = (atomic_t*)lock;
> +	atomic_dec(count);
> +	if (atomic_read(count) >= 0)
> +		return 1;
> +	atomic_inc(count);
> +	return 0;
> +}
>  

Is there a race here between __raw_read_trylock and __raw_write_trylock?

CPU A			CPU B
__raw_read_trylock
atomic_dec(count);
			__raw_write_trylock
			atomic_sub_and_test(RW_LOCK_BIAS, count)
atomic_read(count)

It'd be fairly harmless as neither would manage to get the lock.  But
I think it's not too hard to fix.  Seems to me you want to do:

static inline int __raw_read_trylock(raw_rwlock_t *lock)
{
	atomic_t *count = (atomic_t*)lock;
	if (atomic_dec_return(count) >= 0)
		return 1;
	atomic_inc(count);
	return 0;
}

eliminating the race.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/