From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262207AbVATQNk (ORCPT ); Thu, 20 Jan 2005 11:13:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262202AbVATQM1 (ORCPT ); Thu, 20 Jan 2005 11:12:27 -0500 Received: from mx1.elte.hu ([157.181.1.137]:50892 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S262181AbVATQJP (ORCPT ); Thu, 20 Jan 2005 11:09:15 -0500 Date: Thu, 20 Jan 2005 17:08:39 +0100 From: Ingo Molnar To: Linus Torvalds Cc: Peter Chubb , Chris Wedgwood , Andrew Morton , paulus@samba.org, linux-kernel@vger.kernel.org, tony.luck@intel.com, dsw@gelato.unsw.edu.au, benh@kernel.crashing.org, linux-ia64@vger.kernel.org, hch@infradead.org, wli@holomorphy.com, jbarnes@sgi.com Subject: [patch 1/3] spinlock fix #1, *_can_lock() primitives Message-ID: <20050120160839.GA13067@elte.hu> References: <16877.42598.336096.561224@wombat.chubb.wattle.id.au> <20050119080403.GB29037@elte.hu> <16878.9678.73202.771962@wombat.chubb.wattle.id.au> <20050119092013.GA2045@elte.hu> <16878.54402.344079.528038@cargo.ozlabs.ibm.com> <20050120023445.GA3475@taniwha.stupidest.org> <20050119190104.71f0a76f.akpm@osdl.org> <20050120031854.GA8538@taniwha.stupidest.org> <16879.29449.734172.893834@wombat.chubb.wattle.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Linus Torvalds wrote: > We have a sense problem with the "trylock()" cases - some return "it > was locked" (semaphores), and some return "I succeeded" (spinlocks), > so not only is the sense not immediately obvious from the usage, it's > actually _different_ for semaphores and for spinlocks. well, this is primarily a problem of the semaphore primitives. anyway, here's my first patch again, with s/trylock_test/can_lock/. Ingo -- it fixes the BUILD_LOCK_OPS() bug by introducing the following 3 new locking primitives: spin_can_lock(lock) read_can_lock(lock) write_can_lock(lock) this is what is needed by BUILD_LOCK_OPS(): a nonintrusive test to check whether the real (intrusive) trylock op would succeed or not. Semantics and naming is completely symmetric to the trylock counterpart. No changes to exit.c. build/boot-tested on x86. Architectures that want to support PREEMPT need to add these definitions. Signed-off-by: Ingo Molnar --- linux/kernel/spinlock.c.orig +++ linux/kernel/spinlock.c @@ -173,8 +173,8 @@ EXPORT_SYMBOL(_write_lock); * (We do this in a function because inlining it would be excessive.) */ -#define BUILD_LOCK_OPS(op, locktype, is_locked_fn) \ -void __lockfunc _##op##_lock(locktype *lock) \ +#define BUILD_LOCK_OPS(op, locktype) \ +void __lockfunc _##op##_lock(locktype##_t *lock) \ { \ preempt_disable(); \ for (;;) { \ @@ -183,7 +183,7 @@ void __lockfunc _##op##_lock(locktype *l preempt_enable(); \ if (!(lock)->break_lock) \ (lock)->break_lock = 1; \ - while (is_locked_fn(lock) && (lock)->break_lock) \ + while (!op##_can_lock(lock) && (lock)->break_lock) \ cpu_relax(); \ preempt_disable(); \ } \ @@ -191,7 +191,7 @@ void __lockfunc _##op##_lock(locktype *l \ EXPORT_SYMBOL(_##op##_lock); \ \ -unsigned long __lockfunc _##op##_lock_irqsave(locktype *lock) \ +unsigned long __lockfunc _##op##_lock_irqsave(locktype##_t *lock) \ { \ unsigned long flags; \ \ @@ -205,7 +205,7 @@ unsigned long __lockfunc _##op##_lock_ir preempt_enable(); \ if (!(lock)->break_lock) \ (lock)->break_lock = 1; \ - while (is_locked_fn(lock) && (lock)->break_lock) \ + while (!op##_can_lock(lock) && (lock)->break_lock) \ cpu_relax(); \ preempt_disable(); \ } \ @@ -214,14 +214,14 @@ unsigned long __lockfunc _##op##_lock_ir \ EXPORT_SYMBOL(_##op##_lock_irqsave); \ \ -void __lockfunc _##op##_lock_irq(locktype *lock) \ +void __lockfunc _##op##_lock_irq(locktype##_t *lock) \ { \ _##op##_lock_irqsave(lock); \ } \ \ EXPORT_SYMBOL(_##op##_lock_irq); \ \ -void __lockfunc _##op##_lock_bh(locktype *lock) \ +void __lockfunc _##op##_lock_bh(locktype##_t *lock) \ { \ unsigned long flags; \ \ @@ -246,9 +246,9 @@ EXPORT_SYMBOL(_##op##_lock_bh) * _[spin|read|write]_lock_irqsave() * _[spin|read|write]_lock_bh() */ -BUILD_LOCK_OPS(spin, spinlock_t, spin_is_locked); -BUILD_LOCK_OPS(read, rwlock_t, rwlock_is_locked); -BUILD_LOCK_OPS(write, rwlock_t, spin_is_locked); +BUILD_LOCK_OPS(spin, spinlock); +BUILD_LOCK_OPS(read, rwlock); +BUILD_LOCK_OPS(write, rwlock); #endif /* CONFIG_PREEMPT */ --- linux/include/linux/spinlock.h.orig +++ linux/include/linux/spinlock.h @@ -584,4 +584,10 @@ static inline int bit_spin_is_locked(int #define DEFINE_SPINLOCK(x) spinlock_t x = SPIN_LOCK_UNLOCKED #define DEFINE_RWLOCK(x) rwlock_t x = RW_LOCK_UNLOCKED +/** + * spin_can_lock - would spin_trylock() succeed? + * @lock: the spinlock in question. + */ +#define spin_can_lock(lock) (!spin_is_locked(lock)) + #endif /* __LINUX_SPINLOCK_H */ --- linux/include/asm-i386/spinlock.h.orig +++ linux/include/asm-i386/spinlock.h @@ -188,6 +188,18 @@ typedef struct { #define rwlock_is_locked(x) ((x)->lock != RW_LOCK_BIAS) +/** + * read_can_lock - would read_trylock() succeed? + * @lock: the rwlock in question. + */ +#define read_can_lock(x) (atomic_read((atomic_t *)&(x)->lock) > 0) + +/** + * write_can_lock - would write_trylock() succeed? + * @lock: the rwlock in question. + */ +#define write_can_lock(x) ((x)->lock == RW_LOCK_BIAS) + /* * On x86, we implement read-write locks as a 32-bit counter * with the high bit (sign) being the "contended" bit.