From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 29 Jul 2002 04:09:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 29 Jul 2002 04:09:53 -0400 Received: from dell-paw-3.cambridge.redhat.com ([195.224.55.237]:46069 "EHLO executor.cambridge.redhat.com") by vger.kernel.org with ESMTP id ; Mon, 29 Jul 2002 04:09:50 -0400 To: torvalds@transmeta.com, Christoph Hellwig , dhowells@redhat.com, linux-kernel@vger.kernel.org Subject: [PATCH] rwsem trylock and downgrade part II In-Reply-To: Message from Christoph Hellwig of "Sun, 28 Jul 2002 20:24:19 +0200." <20020728202419.A24944@lst.de> User-Agent: EMH/1.14.1 SEMI/1.14.3 (Ushinoya) FLIM/1.14.3 (=?ISO-8859-4?Q?Unebigory=F2mae?=) APEL/10.3 Emacs/21.2 (i386-redhat-linux-gnu) MULE/5.0 (SAKAKI) MIME-Version: 1.0 (generated by SEMI 1.14.3 - "Ushinoya") Content-Type: text/plain; charset=US-ASCII Date: Mon, 29 Jul 2002 09:12:56 +0100 Message-ID: <17496.1027930376@warthog.cambridge.redhat.com> From: David Howells Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi Linus, Christoph, I'm not sure what happened, but I think I applied an old incomplete patch when patching 2.5.28, one that was missing Christoph's rwsem-spinlock stuff and the trylock stuff. The attached patch adds these back (as per Christoph's patch), it also adds a missing export to lib/rwsem.c. When compiled for PentiumIII SMP, I see: dhowells>nm vmlinux | grep rwsem c01c5dbd t .text.lock.rwsem c02995a0 ? __kstrtab_rwsem_down_read_failed c02995b7 ? __kstrtab_rwsem_down_write_failed c02995da ? __kstrtab_rwsem_downgrade_wake c02995cf ? __kstrtab_rwsem_wake c02a1cf8 ? __ksymtab_rwsem_down_read_failed c02a1d00 ? __ksymtab_rwsem_down_write_failed c02a1d10 ? __ksymtab_rwsem_downgrade_wake c02a1d08 ? __ksymtab_rwsem_wake c01c5870 T rwsem_down_read_failed c01c5a20 T rwsem_down_write_failed c01c5cf0 T rwsem_downgrade_wake c01c5bd0 T rwsem_wake When compiled for i386 SMP, I see: dhowells>nm vmlinux | grep 'rwsem\|__\(up\|down.*\)_\(read\|write\)' c01be49a t .text.lock.rwsem_spinlock c01bdf8c T __down_read c01be080 T __down_read_trylock c01be0f4 T __down_write c01be1ec T __down_write_trylock c01be3e4 T __downgrade_write c028c0f9 ? __kstrtab___down_read c028c120 ? __kstrtab___down_read_trylock c028c142 ? __kstrtab___down_write c028c160 ? __kstrtab___down_write_trylock c028c1c0 ? __kstrtab___downgrade_write c028c183 ? __kstrtab___up_read c028c19b ? __kstrtab___up_write c028c0e0 ? __kstrtab_init_rwsem c0295b80 ? __ksymtab___down_read c0295b88 ? __ksymtab___down_read_trylock c0295b90 ? __ksymtab___down_write c0295b98 ? __ksymtab___down_write_trylock c0295bb0 ? __ksymtab___downgrade_write c0295ba0 ? __ksymtab___up_read c0295ba8 ? __ksymtab___up_write c0295b78 ? __ksymtab_init_rwsem c01be264 T __up_read c01be2fc T __up_write c01bdf6c T init_rwsem So I think I've got all the functions there and that they're all exported now. David diff -uNr linux-2.5.29/include/asm-i386/rwsem.h linux-rwsem-2529/include/asm-i386/rwsem.h --- linux-2.5.29/include/asm-i386/rwsem.h Mon Jul 29 08:26:56 2002 +++ linux-rwsem-2529/include/asm-i386/rwsem.h Mon Jul 29 08:32:49 2002 @@ -118,6 +118,29 @@ } /* + * trylock for reading -- returns 1 if successful, 0 if contention + */ +static inline int __down_read_trylock(struct rw_semaphore *sem) +{ + __s32 result, tmp; + __asm__ __volatile__( + "# beginning __down_read_trylock\n\t" + " movl %0,%1\n\t" + "1:\n\t" + " movl %1,%2\n\t" + " addl %3,%2\n\t" + " jle 2f\n\t" +LOCK_PREFIX " cmpxchgl %2,%0\n\t" + " jnz 1b\n\t" + "2:\n\t" + "# ending __down_read_trylock\n\t" + : "+m"(sem->count), "=&a"(result), "=&r"(tmp) + : "i"(RWSEM_ACTIVE_READ_BIAS) + : "memory", "cc"); + return result>=0 ? 1 : 0; +} + +/* * lock for writing */ static inline void __down_write(struct rw_semaphore *sem) @@ -145,6 +168,19 @@ } /* + * trylock for writing -- returns 1 if successful, 0 if contention + */ +static inline int __down_write_trylock(struct rw_semaphore *sem) +{ + signed long ret = cmpxchg(&sem->count, + RWSEM_UNLOCKED_VALUE, + RWSEM_ACTIVE_WRITE_BIAS); + if (ret == RWSEM_UNLOCKED_VALUE) + return 1; + return 0; +} + +/* * unlock after reading */ static inline void __up_read(struct rw_semaphore *sem) diff -uNr linux-2.5.29/include/linux/rwsem-spinlock.h linux-rwsem-2529/include/linux/rwsem-spinlock.h --- linux-2.5.29/include/linux/rwsem-spinlock.h Thu Jul 11 19:35:21 2002 +++ linux-rwsem-2529/include/linux/rwsem-spinlock.h Mon Jul 29 08:32:49 2002 @@ -54,9 +54,12 @@ extern void FASTCALL(init_rwsem(struct rw_semaphore *sem)); extern void FASTCALL(__down_read(struct rw_semaphore *sem)); +extern int FASTCALL(__down_read_trylock(struct rw_semaphore *sem)); extern void FASTCALL(__down_write(struct rw_semaphore *sem)); +extern int FASTCALL(__down_write_trylock(struct rw_semaphore *sem)); extern void FASTCALL(__up_read(struct rw_semaphore *sem)); extern void FASTCALL(__up_write(struct rw_semaphore *sem)); +extern void FASTCALL(__downgrade_write(struct rw_semaphore *sem)); #endif /* __KERNEL__ */ #endif /* _LINUX_RWSEM_SPINLOCK_H */ diff -uNr linux-2.5.29/include/linux/rwsem.h linux-rwsem-2529/include/linux/rwsem.h --- linux-2.5.29/include/linux/rwsem.h Mon Jul 29 08:26:57 2002 +++ linux-rwsem-2529/include/linux/rwsem.h Mon Jul 29 08:32:49 2002 @@ -46,6 +46,18 @@ } /* + * trylock for reading -- returns 1 if successful, 0 if contention + */ +static inline int down_read_trylock(struct rw_semaphore *sem) +{ + int ret; + rwsemtrace(sem,"Entering down_read_trylock"); + ret = __down_read_trylock(sem); + rwsemtrace(sem,"Leaving down_read_trylock"); + return ret; +} + +/* * lock for writing */ static inline void down_write(struct rw_semaphore *sem) @@ -56,6 +68,18 @@ } /* + * trylock for writing -- returns 1 if successful, 0 if contention + */ +static inline int down_write_trylock(struct rw_semaphore *sem) +{ + int ret; + rwsemtrace(sem,"Entering down_write_trylock"); + ret = __down_write_trylock(sem); + rwsemtrace(sem,"Leaving down_write_trylock"); + return ret; +} + +/* * release a read lock */ static inline void up_read(struct rw_semaphore *sem) @@ -85,6 +109,5 @@ rwsemtrace(sem,"Leaving downgrade_write"); } - #endif /* __KERNEL__ */ #endif /* _LINUX_RWSEM_H */ diff -uNr linux-2.5.29/lib/rwsem-spinlock.c linux-rwsem-2529/lib/rwsem-spinlock.c --- linux-2.5.29/lib/rwsem-spinlock.c Thu Jul 11 19:35:17 2002 +++ linux-rwsem-2529/lib/rwsem-spinlock.c Mon Jul 29 08:32:49 2002 @@ -46,8 +46,9 @@ * - the 'waiting count' is non-zero * - the spinlock must be held by the caller * - woken process blocks are discarded from the list after having flags zeroised + * - writers are only woken if wakewrite is non-zero */ -static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem) +static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) { struct rwsem_waiter *waiter; int woken; @@ -56,7 +57,14 @@ waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list); - /* try to grant a single write lock if there's a writer at the front of the queue + if (!wakewrite) { + if (waiter->flags & RWSEM_WAITING_FOR_WRITE) + goto out; + goto dont_wake_writers; + } + + /* if we are allowed to wake writers try to grant a single write lock if there's a + * writer at the front of the queue * - we leave the 'waiting count' incremented to signify potential contention */ if (waiter->flags & RWSEM_WAITING_FOR_WRITE) { @@ -68,16 +76,19 @@ } /* grant an infinite number of read locks to the readers at the front of the queue */ + dont_wake_writers: woken = 0; - do { + while (waiter->flags&RWSEM_WAITING_FOR_READ) { + struct list_head *next = waiter->list.next; + list_del(&waiter->list); waiter->flags = 0; wake_up_process(waiter->task); woken++; if (list_empty(&sem->wait_list)) break; - waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list); - } while (waiter->flags&RWSEM_WAITING_FOR_READ); + waiter = list_entry(next,struct rwsem_waiter,list); + } sem->activity += woken; @@ -149,6 +160,28 @@ } /* + * trylock for reading -- returns 1 if successful, 0 if contention + */ +int __down_read_trylock(struct rw_semaphore *sem) +{ + int ret = 0; + rwsemtrace(sem,"Entering __down_read_trylock"); + + spin_lock(&sem->wait_lock); + + if (sem->activity>=0 && list_empty(&sem->wait_list)) { + /* granted */ + sem->activity++; + ret = 1; + } + + spin_unlock(&sem->wait_lock); + + rwsemtrace(sem,"Leaving __down_read_trylock"); + return ret; +} + +/* * get a write lock on the semaphore * - note that we increment the waiting count anyway to indicate an exclusive lock */ @@ -195,6 +228,28 @@ } /* + * trylock for writing -- returns 1 if successful, 0 if contention + */ +int __down_write_trylock(struct rw_semaphore *sem) +{ + int ret = 0; + rwsemtrace(sem,"Entering __down_write_trylock"); + + spin_lock(&sem->wait_lock); + + if (sem->activity==0 && list_empty(&sem->wait_list)) { + /* granted */ + sem->activity = -1; + ret = 1; + } + + spin_unlock(&sem->wait_lock); + + rwsemtrace(sem,"Leaving __down_write_trylock"); + return ret; +} + +/* * release a read lock on the semaphore */ void __up_read(struct rw_semaphore *sem) @@ -222,18 +277,40 @@ sem->activity = 0; if (!list_empty(&sem->wait_list)) - sem = __rwsem_do_wake(sem); + sem = __rwsem_do_wake(sem, 1); spin_unlock(&sem->wait_lock); rwsemtrace(sem,"Leaving __up_write"); } +/* + * downgrade a write lock into a read lock + * - just wake up any readers at the front of the queue + */ +void __downgrade_write(struct rw_semaphore *sem) +{ + rwsemtrace(sem,"Entering __rwsem_downgrade"); + + spin_lock(&sem->wait_lock); + + sem->activity = 1; + if (!list_empty(&sem->wait_list)) + sem = __rwsem_do_wake(sem,0); + + spin_unlock(&sem->wait_lock); + + rwsemtrace(sem,"Leaving __rwsem_downgrade"); +} + EXPORT_SYMBOL(init_rwsem); EXPORT_SYMBOL(__down_read); +EXPORT_SYMBOL(__down_read_trylock); EXPORT_SYMBOL(__down_write); +EXPORT_SYMBOL(__down_write_trylock); EXPORT_SYMBOL(__up_read); EXPORT_SYMBOL(__up_write); +EXPORT_SYMBOL(__downgrade_write); #if RWSEM_DEBUG EXPORT_SYMBOL(rwsemtrace); #endif diff -uNr linux-2.5.29/lib/rwsem.c linux-rwsem-2529/lib/rwsem.c --- linux-2.5.29/lib/rwsem.c Mon Jul 29 08:26:57 2002 +++ linux-rwsem-2529/lib/rwsem.c Mon Jul 29 08:35:47 2002 @@ -236,6 +236,7 @@ EXPORT_SYMBOL_NOVERS(rwsem_down_read_failed); EXPORT_SYMBOL_NOVERS(rwsem_down_write_failed); EXPORT_SYMBOL_NOVERS(rwsem_wake); +EXPORT_SYMBOL_NOVERS(rwsem_downgrade_wake); #if RWSEM_DEBUG EXPORT_SYMBOL(rwsemtrace); #endif