From: Nick Piggin Lindent rwsem.c and rwsem-spinlock.c and fix a few things by hand. Also added a couple of comments for the memory barriers. Added the __sched annotation that was left out of rwsem-spinlock.c. Signed-off-by: Andrew Morton --- 25-akpm/lib/rwsem-spinlock.c | 97 ++++++++++++++++++++------------------ 25-akpm/lib/rwsem.c | 109 +++++++++++++++++++++++-------------------- 2 files changed, 110 insertions(+), 96 deletions(-) diff -puN lib/rwsem.c~lindent-rwsem lib/rwsem.c --- 25/lib/rwsem.c~lindent-rwsem 2004-06-20 02:48:25.273508152 -0700 +++ 25-akpm/lib/rwsem.c 2004-06-20 02:48:25.281506936 -0700 @@ -9,9 +9,9 @@ #include struct rwsem_waiter { - struct list_head list; - struct task_struct *task; - unsigned int flags; + struct list_head list; + struct task_struct *task; + unsigned int flags; #define RWSEM_WAITING_FOR_READ 0x00000001 #define RWSEM_WAITING_FOR_WRITE 0x00000002 }; @@ -20,31 +20,32 @@ struct rwsem_waiter { #undef rwsemtrace void rwsemtrace(struct rw_semaphore *sem, const char *str) { - printk("sem=%p\n",sem); - printk("(sem)=%08lx\n",sem->count); + printk("sem=%p\n", sem); + printk("(sem)=%08lx\n", sem->count); if (sem->debug) - printk("[%d] %s({%08lx})\n",current->pid,str,sem->count); + printk("[%d] %s({%08lx})\n", current->pid, str, sem->count); } #endif /* - * handle the lock being released whilst there are processes blocked on it that can now run + * handle the lock release when processes blocked on it that can now run * - if we come here from up_xxxx(), then: - * - the 'active part' of the count (&0x0000ffff) had reached zero (but may have changed) - * - the 'waiting part' of the count (&0xffff0000) is negative (and will still be so) + * - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed) + * - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so) * - there must be someone on the queue * - the spinlock must be held by the caller * - woken process blocks are discarded from the list after having task zeroed * - writers are only woken if downgrading is false */ -static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int downgrading) +static inline struct rw_semaphore * +__rwsem_do_wake(struct rw_semaphore *sem, int downgrading) { struct rwsem_waiter *waiter; struct task_struct *tsk; struct list_head *next; signed long oldcount, woken, loop; - rwsemtrace(sem,"Entering __rwsem_do_wake"); + rwsemtrace(sem, "Entering __rwsem_do_wake"); if (downgrading) goto dont_wake_writers; @@ -53,19 +54,24 @@ static inline struct rw_semaphore *__rws * if we can transition the active part of the count from 0 -> 1 */ try_again: - oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS,sem) - RWSEM_ACTIVE_BIAS; + oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS, sem) + - RWSEM_ACTIVE_BIAS; if (oldcount & RWSEM_ACTIVE_MASK) goto undo; - waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list); + 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 - * - note we leave the 'active part' of the count incremented by 1 and the waiting part - * incremented by 0x00010000 + /* try to grant a single write lock if there's a writer at the front + * of the queue - note we leave the 'active part' of the count + * incremented by 1 and the waiting part incremented by 0x00010000 */ if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE)) goto readers_only; + /* We must be careful not to touch 'waiter' after we set ->task = NULL. + * It is an allocated on the waiter's stack and may become invalid at + * any time after that point (due to a wakeup from another source). + */ list_del(&waiter->list); tsk = waiter->task; mb(); @@ -76,7 +82,7 @@ static inline struct rw_semaphore *__rws /* don't want to wake any writers */ dont_wake_writers: - waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list); + waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (waiter->flags & RWSEM_WAITING_FOR_WRITE) goto out; @@ -90,23 +96,25 @@ static inline struct rw_semaphore *__rws do { woken++; - if (waiter->list.next==&sem->wait_list) + if (waiter->list.next == &sem->wait_list) break; - waiter = list_entry(waiter->list.next,struct rwsem_waiter,list); + waiter = list_entry(waiter->list.next, + struct rwsem_waiter, list); } while (waiter->flags & RWSEM_WAITING_FOR_READ); loop = woken; woken *= RWSEM_ACTIVE_BIAS - RWSEM_WAITING_BIAS; if (!downgrading) - woken -= RWSEM_ACTIVE_BIAS; /* we'd already done one increment - * earlier */ - rwsem_atomic_add(woken,sem); + /* we'd already done one increment earlier */ + woken -= RWSEM_ACTIVE_BIAS; + + rwsem_atomic_add(woken, sem); next = sem->wait_list.next; - for (; loop>0; loop--) { - waiter = list_entry(next,struct rwsem_waiter,list); + for (; loop > 0; loop--) { + waiter = list_entry(next, struct rwsem_waiter, list); next = waiter->list.next; tsk = waiter->task; mb(); @@ -119,12 +127,12 @@ static inline struct rw_semaphore *__rws next->prev = &sem->wait_list; out: - rwsemtrace(sem,"Leaving __rwsem_do_wake"); + rwsemtrace(sem, "Leaving __rwsem_do_wake"); return sem; /* undo the change to count, but check for a transition 1->0 */ undo: - if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS,sem)!=0) + if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) != 0) goto out; goto try_again; } @@ -132,28 +140,26 @@ static inline struct rw_semaphore *__rws /* * wait for a lock to be granted */ -static inline struct rw_semaphore *rwsem_down_failed_common(struct rw_semaphore *sem, - struct rwsem_waiter *waiter, - signed long adjustment) +static inline struct rw_semaphore * +rwsem_down_failed_common(struct rw_semaphore *sem, + struct rwsem_waiter *waiter, signed long adjustment) { struct task_struct *tsk = current; signed long count; - set_task_state(tsk,TASK_UNINTERRUPTIBLE); + set_task_state(tsk, TASK_UNINTERRUPTIBLE); /* set up my own style of waitqueue */ spin_lock(&sem->wait_lock); waiter->task = tsk; get_task_struct(tsk); - list_add_tail(&waiter->list,&sem->wait_list); + list_add_tail(&waiter->list, &sem->wait_list); - /* note that we're now waiting on the lock, but no longer actively read-locking */ - count = rwsem_atomic_update(adjustment,sem); + /* we're now waiting on the lock, but no longer actively read-locking */ + count = rwsem_atomic_update(adjustment, sem); - /* if there are no longer active locks, wake the front queued process(es) up - * - it might even be this process, since the waker takes a more active part - */ + /* if there are no active locks, wake the front queued process(es) up */ if (!(count & RWSEM_ACTIVE_MASK)) sem = __rwsem_do_wake(sem, 0); @@ -175,42 +181,45 @@ static inline struct rw_semaphore *rwsem /* * wait for the read lock to be granted */ -struct rw_semaphore fastcall __sched *rwsem_down_read_failed(struct rw_semaphore *sem) +struct rw_semaphore fastcall __sched * +rwsem_down_read_failed(struct rw_semaphore *sem) { struct rwsem_waiter waiter; - rwsemtrace(sem,"Entering rwsem_down_read_failed"); + rwsemtrace(sem, "Entering rwsem_down_read_failed"); waiter.flags = RWSEM_WAITING_FOR_READ; - rwsem_down_failed_common(sem,&waiter,RWSEM_WAITING_BIAS-RWSEM_ACTIVE_BIAS); + rwsem_down_failed_common(sem, &waiter, + RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS); - rwsemtrace(sem,"Leaving rwsem_down_read_failed"); + rwsemtrace(sem, "Leaving rwsem_down_read_failed"); return sem; } /* * wait for the write lock to be granted */ -struct rw_semaphore fastcall __sched *rwsem_down_write_failed(struct rw_semaphore *sem) +struct rw_semaphore fastcall __sched * +rwsem_down_write_failed(struct rw_semaphore *sem) { struct rwsem_waiter waiter; - rwsemtrace(sem,"Entering rwsem_down_write_failed"); + rwsemtrace(sem, "Entering rwsem_down_write_failed"); waiter.flags = RWSEM_WAITING_FOR_WRITE; - rwsem_down_failed_common(sem,&waiter,-RWSEM_ACTIVE_BIAS); + rwsem_down_failed_common(sem, &waiter, -RWSEM_ACTIVE_BIAS); - rwsemtrace(sem,"Leaving rwsem_down_write_failed"); + rwsemtrace(sem, "Leaving rwsem_down_write_failed"); return sem; } /* * handle waking up a waiter on the semaphore - * - up_read/up_write has decremented the active part of the count if we come here + * - up_read/up_write has decremented the active part of count if we come here */ struct rw_semaphore fastcall *rwsem_wake(struct rw_semaphore *sem) { - rwsemtrace(sem,"Entering rwsem_wake"); + rwsemtrace(sem, "Entering rwsem_wake"); spin_lock(&sem->wait_lock); @@ -220,19 +229,19 @@ struct rw_semaphore fastcall *rwsem_wake spin_unlock(&sem->wait_lock); - rwsemtrace(sem,"Leaving rwsem_wake"); + rwsemtrace(sem, "Leaving rwsem_wake"); return sem; } /* * downgrade a write lock into a read lock - * - caller incremented waiting part of count, and discovered it to be still negative + * - caller incremented waiting part of count and discovered it still negative * - just wake up any readers at the front of the queue */ struct rw_semaphore fastcall *rwsem_downgrade_wake(struct rw_semaphore *sem) { - rwsemtrace(sem,"Entering rwsem_downgrade_wake"); + rwsemtrace(sem, "Entering rwsem_downgrade_wake"); spin_lock(&sem->wait_lock); @@ -242,7 +251,7 @@ struct rw_semaphore fastcall *rwsem_down spin_unlock(&sem->wait_lock); - rwsemtrace(sem,"Leaving rwsem_downgrade_wake"); + rwsemtrace(sem, "Leaving rwsem_downgrade_wake"); return sem; } diff -puN lib/rwsem-spinlock.c~lindent-rwsem lib/rwsem-spinlock.c --- 25/lib/rwsem-spinlock.c~lindent-rwsem 2004-06-20 02:48:25.275507848 -0700 +++ 25-akpm/lib/rwsem-spinlock.c 2004-06-20 02:48:25.282506784 -0700 @@ -1,5 +1,5 @@ -/* rwsem-spinlock.c: R/W semaphores: contention handling functions for generic spinlock - * implementation +/* rwsem-spinlock.c: R/W semaphores: contention handling functions for + * generic spinlock implementation * * Copyright (c) 2001 David Howells (dhowells@redhat.com). * - Derived partially from idea by Andrea Arcangeli @@ -10,9 +10,9 @@ #include struct rwsem_waiter { - struct list_head list; - struct task_struct *task; - unsigned int flags; + struct list_head list; + struct task_struct *task; + unsigned int flags; #define RWSEM_WAITING_FOR_READ 0x00000001 #define RWSEM_WAITING_FOR_WRITE 0x00000002 }; @@ -22,7 +22,8 @@ void rwsemtrace(struct rw_semaphore *sem { if (sem->debug) printk("[%d] %s({%d,%d})\n", - current->pid,str,sem->activity,list_empty(&sem->wait_list)?0:1); + current->pid, str, sem->activity, + list_empty(&sem->wait_list) ? 0 : 1); } #endif @@ -40,7 +41,7 @@ void fastcall init_rwsem(struct rw_semap } /* - * handle the lock being released whilst there are processes blocked on it that can now run + * handle the lock release when processes blocked on it that can now run * - if we come here, then: * - the 'active count' _reached_ zero * - the 'waiting count' is non-zero @@ -48,15 +49,16 @@ void fastcall init_rwsem(struct rw_semap * - woken process blocks are discarded from the list after having task zeroed * - writers are only woken if wakewrite is non-zero */ -static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) +static inline struct rw_semaphore * +__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite) { struct rwsem_waiter *waiter; struct task_struct *tsk; int woken; - rwsemtrace(sem,"Entering __rwsem_do_wake"); + rwsemtrace(sem, "Entering __rwsem_do_wake"); - waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list); + waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (!wakewrite) { if (waiter->flags & RWSEM_WAITING_FOR_WRITE) @@ -64,14 +66,16 @@ static inline struct rw_semaphore *__rws 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 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) { sem->activity = -1; list_del(&waiter->list); tsk = waiter->task; + /* Don't touch waiter after ->task has been NULLed */ mb(); waiter->task = NULL; wake_up_process(tsk); @@ -79,10 +83,10 @@ static inline struct rw_semaphore *__rws goto out; } - /* grant an infinite number of read locks to the readers at the front of the queue */ + /* grant an infinite number of read locks to the front of the queue */ dont_wake_writers: woken = 0; - while (waiter->flags&RWSEM_WAITING_FOR_READ) { + while (waiter->flags & RWSEM_WAITING_FOR_READ) { struct list_head *next = waiter->list.next; list_del(&waiter->list); @@ -94,27 +98,28 @@ static inline struct rw_semaphore *__rws woken++; if (list_empty(&sem->wait_list)) break; - waiter = list_entry(next,struct rwsem_waiter,list); + waiter = list_entry(next, struct rwsem_waiter, list); } sem->activity += woken; out: - rwsemtrace(sem,"Leaving __rwsem_do_wake"); + rwsemtrace(sem, "Leaving __rwsem_do_wake"); return sem; } /* * wake a single writer */ -static inline struct rw_semaphore *__rwsem_wake_one_writer(struct rw_semaphore *sem) +static inline struct rw_semaphore * +__rwsem_wake_one_writer(struct rw_semaphore *sem) { struct rwsem_waiter *waiter; struct task_struct *tsk; sem->activity = -1; - waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list); + waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); list_del(&waiter->list); tsk = waiter->task; @@ -128,16 +133,16 @@ static inline struct rw_semaphore *__rws /* * get a read lock on the semaphore */ -void fastcall __down_read(struct rw_semaphore *sem) +void fastcall __sched __down_read(struct rw_semaphore *sem) { struct rwsem_waiter waiter; struct task_struct *tsk; - rwsemtrace(sem,"Entering __down_read"); + rwsemtrace(sem, "Entering __down_read"); spin_lock(&sem->wait_lock); - if (sem->activity>=0 && list_empty(&sem->wait_list)) { + if (sem->activity >= 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity++; spin_unlock(&sem->wait_lock); @@ -145,14 +150,14 @@ void fastcall __down_read(struct rw_sema } tsk = current; - set_task_state(tsk,TASK_UNINTERRUPTIBLE); + set_task_state(tsk, TASK_UNINTERRUPTIBLE); /* set up my own style of waitqueue */ waiter.task = tsk; waiter.flags = RWSEM_WAITING_FOR_READ; get_task_struct(tsk); - list_add_tail(&waiter.list,&sem->wait_list); + list_add_tail(&waiter.list, &sem->wait_list); /* we don't need to touch the semaphore struct anymore */ spin_unlock(&sem->wait_lock); @@ -168,7 +173,7 @@ void fastcall __down_read(struct rw_sema tsk->state = TASK_RUNNING; out: - rwsemtrace(sem,"Leaving __down_read"); + rwsemtrace(sem, "Leaving __down_read"); } /* @@ -177,11 +182,11 @@ void fastcall __down_read(struct rw_sema int fastcall __down_read_trylock(struct rw_semaphore *sem) { int ret = 0; - rwsemtrace(sem,"Entering __down_read_trylock"); + rwsemtrace(sem, "Entering __down_read_trylock"); spin_lock(&sem->wait_lock); - if (sem->activity>=0 && list_empty(&sem->wait_list)) { + if (sem->activity >= 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity++; ret = 1; @@ -189,24 +194,24 @@ int fastcall __down_read_trylock(struct spin_unlock(&sem->wait_lock); - rwsemtrace(sem,"Leaving __down_read_trylock"); + 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 + * - we increment the waiting count anyway to indicate an exclusive lock */ -void fastcall __down_write(struct rw_semaphore *sem) +void fastcall __sched __down_write(struct rw_semaphore *sem) { struct rwsem_waiter waiter; struct task_struct *tsk; - rwsemtrace(sem,"Entering __down_write"); + rwsemtrace(sem, "Entering __down_write"); spin_lock(&sem->wait_lock); - if (sem->activity==0 && list_empty(&sem->wait_list)) { + if (sem->activity == 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity = -1; spin_unlock(&sem->wait_lock); @@ -214,14 +219,14 @@ void fastcall __down_write(struct rw_sem } tsk = current; - set_task_state(tsk,TASK_UNINTERRUPTIBLE); + set_task_state(tsk, TASK_UNINTERRUPTIBLE); /* set up my own style of waitqueue */ waiter.task = tsk; waiter.flags = RWSEM_WAITING_FOR_WRITE; get_task_struct(tsk); - list_add_tail(&waiter.list,&sem->wait_list); + list_add_tail(&waiter.list, &sem->wait_list); /* we don't need to touch the semaphore struct anymore */ spin_unlock(&sem->wait_lock); @@ -237,7 +242,7 @@ void fastcall __down_write(struct rw_sem tsk->state = TASK_RUNNING; out: - rwsemtrace(sem,"Leaving __down_write"); + rwsemtrace(sem, "Leaving __down_write"); } /* @@ -246,11 +251,11 @@ void fastcall __down_write(struct rw_sem int fastcall __down_write_trylock(struct rw_semaphore *sem) { int ret = 0; - rwsemtrace(sem,"Entering __down_write_trylock"); + rwsemtrace(sem, "Entering __down_write_trylock"); spin_lock(&sem->wait_lock); - if (sem->activity==0 && list_empty(&sem->wait_list)) { + if (sem->activity == 0 && list_empty(&sem->wait_list)) { /* granted */ sem->activity = -1; ret = 1; @@ -258,7 +263,7 @@ int fastcall __down_write_trylock(struct spin_unlock(&sem->wait_lock); - rwsemtrace(sem,"Leaving __down_write_trylock"); + rwsemtrace(sem, "Leaving __down_write_trylock"); return ret; } @@ -267,16 +272,16 @@ int fastcall __down_write_trylock(struct */ void fastcall __up_read(struct rw_semaphore *sem) { - rwsemtrace(sem,"Entering __up_read"); + rwsemtrace(sem, "Entering __up_read"); spin_lock(&sem->wait_lock); - if (--sem->activity==0 && !list_empty(&sem->wait_list)) + if (--sem->activity == 0 && !list_empty(&sem->wait_list)) sem = __rwsem_wake_one_writer(sem); spin_unlock(&sem->wait_lock); - rwsemtrace(sem,"Leaving __up_read"); + rwsemtrace(sem, "Leaving __up_read"); } /* @@ -284,7 +289,7 @@ void fastcall __up_read(struct rw_semaph */ void fastcall __up_write(struct rw_semaphore *sem) { - rwsemtrace(sem,"Entering __up_write"); + rwsemtrace(sem, "Entering __up_write"); spin_lock(&sem->wait_lock); @@ -294,7 +299,7 @@ void fastcall __up_write(struct rw_semap spin_unlock(&sem->wait_lock); - rwsemtrace(sem,"Leaving __up_write"); + rwsemtrace(sem, "Leaving __up_write"); } /* @@ -303,17 +308,17 @@ void fastcall __up_write(struct rw_semap */ void fastcall __downgrade_write(struct rw_semaphore *sem) { - rwsemtrace(sem,"Entering __downgrade_write"); + rwsemtrace(sem, "Entering __downgrade_write"); spin_lock(&sem->wait_lock); sem->activity = 1; if (!list_empty(&sem->wait_list)) - sem = __rwsem_do_wake(sem,0); + sem = __rwsem_do_wake(sem, 0); spin_unlock(&sem->wait_lock); - rwsemtrace(sem,"Leaving __downgrade_write"); + rwsemtrace(sem, "Leaving __downgrade_write"); } EXPORT_SYMBOL(init_rwsem); _