[RFC] aio_down() for i386 and x86_64
From: Benjamin LaHaise
Date: Tue Jun 14 2005 - 16:50:02 EST
Hello all,
The patch below (which applies on top of the previous wait_private patch
and the do_sync_(read|write) fix) introduces a new pair of primatives for
semaphores: aio_down() and aio_up(). The aio_down() function takes an
iocb and locks the semaphore for use within the iocb's context. If taking
the semaphore would block, aio_down() returns -EIOCBRETRY and will do an
kick_iocb() on the iocb once the semaphore is acquired.
This is a first pass patch, so please ignore the debugging printk()s.
Any comments on the approach?
-ben
--
"Time is what keeps everything from happening all at once." -- John Wheeler
... v2.6.12-rc6-aio_down-A0.diff
diff -purN 10_wait_private/arch/i386/kernel/semaphore.c aio_down-rc6.diff/arch/i386/kernel/semaphore.c
--- 10_wait_private/arch/i386/kernel/semaphore.c 2005-06-13 02:07:54.000000000 -0400
+++ aio_down-rc6.diff/arch/i386/kernel/semaphore.c 2005-06-14 16:59:56.723150064 -0400
@@ -91,6 +91,55 @@ static fastcall void __attribute_used__
tsk->state = TASK_RUNNING;
}
+static int aio_down_wait(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+ struct kiocb *iocb = io_wait_to_kiocb(wait);
+ struct semaphore *sem = wait->private;
+ int sleepers = sem->sleepers;
+
+ printk("aio_down_wait(%p, %p): contended\n", sem, iocb);
+ /*
+ * Add "everybody else" into it. They aren't
+ * playing, because we own the spinlock in
+ * the wait_queue_head.
+ */
+ if (!atomic_add_negative(sleepers - 1, &sem->count)) {
+ printk("aio_down_wait: got it!\n");
+ sem->sleepers = 0;
+ sem->aio_owner = iocb;
+ list_del_init(&wait->task_list);
+ wake_up_locked(&sem->wait);
+ kick_iocb(iocb);
+ return 1;
+ }
+ sem->sleepers = 1; /* us - see -1 above */
+
+ return 1;
+}
+
+static fastcall int __attribute_used__ __sched __aio_down(struct kiocb *iocb, struct semaphore * sem)
+{
+ unsigned long flags;
+
+ printk("aio_down(%p, %p): contended\n", sem, iocb);
+ if (sem->aio_owner == iocb) {
+ printk("aio_down: own lock\n");
+ atomic_inc(&sem->count); /* undo dec in aio_down() */
+ return 0;
+ }
+
+ spin_lock_irqsave(&sem->wait.lock, flags);
+ iocb->ki_wait.private = sem;
+ iocb->ki_wait.func = aio_down_wait;
+ add_wait_queue_exclusive_locked(&sem->wait, &iocb->ki_wait);
+
+ sem->sleepers++;
+
+ aio_down_wait(&iocb->ki_wait, 0, 0, NULL);
+ spin_unlock_irqrestore(&sem->wait.lock, flags);
+ return -EIOCBRETRY;
+}
+
static fastcall int __attribute_used__ __sched __down_interruptible(struct semaphore * sem)
{
int retval = 0;
@@ -211,6 +260,28 @@ asm(
asm(
".section .sched.text\n"
".align 4\n"
+".globl __aio_down_failed\n"
+"__aio_down_failed:\n\t"
+#if defined(CONFIG_FRAME_POINTER)
+ "pushl %ebp\n\t"
+ "movl %esp,%ebp\n\t"
+#endif
+ "pushl %edx\n\t"
+ "pushl %ecx\n\t"
+ "call __aio_down\n\t"
+ "popl %ecx\n\t"
+ "popl %edx\n\t"
+#if defined(CONFIG_FRAME_POINTER)
+ "movl %ebp,%esp\n\t"
+ "popl %ebp\n\t"
+#endif
+ "ret"
+);
+EXPORT_SYMBOL(__aio_down_failed);
+
+asm(
+".section .sched.text\n"
+".align 4\n"
".globl __down_failed_interruptible\n"
"__down_failed_interruptible:\n\t"
#if defined(CONFIG_FRAME_POINTER)
diff -purN 10_wait_private/arch/x86_64/kernel/semaphore.c aio_down-rc6.diff/arch/x86_64/kernel/semaphore.c
--- 10_wait_private/arch/x86_64/kernel/semaphore.c 2005-06-13 02:07:56.000000000 -0400
+++ aio_down-rc6.diff/arch/x86_64/kernel/semaphore.c 2005-06-14 16:59:56.755145200 -0400
@@ -14,9 +14,8 @@
*/
#include <linux/config.h>
#include <linux/sched.h>
+#include <linux/err.h>
#include <linux/init.h>
-#include <asm/errno.h>
-
#include <asm/semaphore.h>
/*
@@ -92,6 +91,55 @@ void __sched __down(struct semaphore * s
tsk->state = TASK_RUNNING;
}
+static int aio_down_wait(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+ struct kiocb *iocb = io_wait_to_kiocb(wait);
+ struct semaphore *sem = wait->private;
+ int sleepers = sem->sleepers;
+
+ printk("aio_down_wait(%p, %p): contended\n", sem, iocb);
+ /*
+ * Add "everybody else" into it. They aren't
+ * playing, because we own the spinlock in
+ * the wait_queue_head.
+ */
+ if (!atomic_add_negative(sleepers - 1, &sem->count)) {
+ printk("aio_down_wait: got it!\n");
+ sem->sleepers = 0;
+ sem->aio_owner = iocb;
+ list_del_init(&wait->task_list);
+ wake_up_locked(&sem->wait);
+ kick_iocb(iocb);
+ return 1;
+ }
+ sem->sleepers = 1; /* us - see -1 above */
+
+ return 1;
+}
+
+long __aio_down(struct kiocb *iocb, struct semaphore * sem)
+{
+ unsigned long flags;
+
+ printk("aio_down(%p, %p): contended\n", sem, iocb);
+ if (sem->aio_owner == iocb) {
+ printk("aio_down: own lock\n");
+ atomic_inc(&sem->count); /* undo dec in aio_down() */
+ return 0;
+ }
+
+ spin_lock_irqsave(&sem->wait.lock, flags);
+ iocb->ki_wait.private = sem;
+ iocb->ki_wait.func = aio_down_wait;
+ add_wait_queue_exclusive_locked(&sem->wait, &iocb->ki_wait);
+
+ sem->sleepers++;
+
+ aio_down_wait(&iocb->ki_wait, 0, 0, NULL);
+ spin_unlock_irqrestore(&sem->wait.lock, flags);
+ return -EIOCBRETRY;
+}
+
int __sched __down_interruptible(struct semaphore * sem)
{
int retval = 0;
diff -purN 10_wait_private/arch/x86_64/kernel/x8664_ksyms.c aio_down-rc6.diff/arch/x86_64/kernel/x8664_ksyms.c
--- 10_wait_private/arch/x86_64/kernel/x8664_ksyms.c 2005-06-13 02:07:56.000000000 -0400
+++ aio_down-rc6.diff/arch/x86_64/kernel/x8664_ksyms.c 2005-06-14 16:59:56.761144288 -0400
@@ -62,6 +62,7 @@ EXPORT_SYMBOL(pm_idle);
EXPORT_SYMBOL(pm_power_off);
EXPORT_SYMBOL(get_cmos_time);
+EXPORT_SYMBOL(__aio_down_failed);
EXPORT_SYMBOL(__down_failed);
EXPORT_SYMBOL(__down_failed_interruptible);
EXPORT_SYMBOL(__down_failed_trylock);
diff -purN 10_wait_private/arch/x86_64/lib/thunk.S aio_down-rc6.diff/arch/x86_64/lib/thunk.S
--- 10_wait_private/arch/x86_64/lib/thunk.S 2004-12-24 16:34:44.000000000 -0500
+++ aio_down-rc6.diff/arch/x86_64/lib/thunk.S 2005-06-14 16:59:56.784140792 -0400
@@ -47,6 +47,7 @@
thunk __down_failed,__down
thunk_retrax __down_failed_interruptible,__down_interruptible
thunk_retrax __down_failed_trylock,__down_trylock
+ thunk_retrax __aio_down_failed,__aio_down
thunk __up_wakeup,__up
/* SAVE_ARGS below is used only for the .cfi directives it contains. */
diff -purN 10_wait_private/include/asm-i386/semaphore.h aio_down-rc6.diff/include/asm-i386/semaphore.h
--- 10_wait_private/include/asm-i386/semaphore.h 2005-06-13 02:08:02.000000000 -0400
+++ aio_down-rc6.diff/include/asm-i386/semaphore.h 2005-06-14 16:59:56.787140336 -0400
@@ -41,10 +41,12 @@
#include <linux/wait.h>
#include <linux/rwsem.h>
+struct kiocb;
struct semaphore {
atomic_t count;
int sleepers;
wait_queue_head_t wait;
+ struct kiocb *aio_owner;
};
@@ -52,7 +54,8 @@ struct semaphore {
{ \
.count = ATOMIC_INIT(n), \
.sleepers = 0, \
- .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
+ .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait), \
+ .aio_owner = NULL \
}
#define __MUTEX_INITIALIZER(name) \
@@ -75,6 +78,7 @@ static inline void sema_init (struct sem
atomic_set(&sem->count, val);
sem->sleepers = 0;
init_waitqueue_head(&sem->wait);
+ sem->aio_owner = NULL;
}
static inline void init_MUTEX (struct semaphore *sem)
@@ -142,6 +146,32 @@ static inline int down_interruptible(str
}
/*
+ * Non-blockingly attempt to down() a semaphore for use with aio.
+ * Returns zero if we acquired it
+ */
+static inline int aio_down(struct kiocb *iocb, struct semaphore * sem)
+{
+ int result;
+
+ __asm__ __volatile__(
+ "# atomic aio down operation\n\t"
+ LOCK "decl %1\n\t" /* --sem->count */
+ "js 2f\n\t"
+ "movl %3,%2\n"
+ "xorl %0,%0\n"
+ "1:\n"
+ LOCK_SECTION_START("")
+ "2:\tlea %1,%%edx\n\t"
+ "call __aio_down_failed\n\t"
+ "jmp 1b\n"
+ LOCK_SECTION_END
+ :"=a" (result), "+m" (sem->count), "=m" (sem->aio_owner)
+ :"0" (iocb)
+ :"memory","cc","dx");
+ return result;
+}
+
+/*
* Non-blockingly attempt to down() a semaphore.
* Returns zero if we acquired it
*/
@@ -190,5 +220,14 @@ static inline void up(struct semaphore *
:"memory","ax");
}
+static inline void aio_up(struct kiocb *iocb, struct semaphore *sem)
+{
+#ifdef CONFIG_DEBUG_KERNEL
+ BUG_ON(sem->aio_owner != iocb);
+#endif
+ sem->aio_owner = NULL;
+ up(sem);
+}
+
#endif
#endif
diff -purN 10_wait_private/include/asm-x86_64/semaphore.h aio_down-rc6.diff/include/asm-x86_64/semaphore.h
--- 10_wait_private/include/asm-x86_64/semaphore.h 2004-12-24 16:33:48.000000000 -0500
+++ aio_down-rc6.diff/include/asm-x86_64/semaphore.h 2005-06-14 16:59:56.794139272 -0400
@@ -43,17 +43,20 @@
#include <linux/rwsem.h>
#include <linux/stringify.h>
+struct kiocb;
struct semaphore {
atomic_t count;
int sleepers;
wait_queue_head_t wait;
+ struct kiocb *aio_owner;
};
#define __SEMAPHORE_INITIALIZER(name, n) \
{ \
.count = ATOMIC_INIT(n), \
.sleepers = 0, \
- .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
+ .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait), \
+ .aio_owner = NULL \
}
#define __MUTEX_INITIALIZER(name) \
@@ -76,6 +79,7 @@ static inline void sema_init (struct sem
atomic_set(&sem->count, val);
sem->sleepers = 0;
init_waitqueue_head(&sem->wait);
+ sem->aio_owner = NULL;
}
static inline void init_MUTEX (struct semaphore *sem)
@@ -88,11 +92,13 @@ static inline void init_MUTEX_LOCKED (st
sema_init(sem, 0);
}
+asmlinkage long __aio_down_failed(void /* special register calling convention */);
asmlinkage void __down_failed(void /* special register calling convention */);
asmlinkage int __down_failed_interruptible(void /* params in registers */);
asmlinkage int __down_failed_trylock(void /* params in registers */);
asmlinkage void __up_wakeup(void /* special register calling convention */);
+asmlinkage long __aio_down(struct kiocb *iocb, struct semaphore * sem);
asmlinkage void __down(struct semaphore * sem);
asmlinkage int __down_interruptible(struct semaphore * sem);
asmlinkage int __down_trylock(struct semaphore * sem);
@@ -148,6 +154,32 @@ static inline int down_interruptible(str
}
/*
+ * Non-blockingly attempt to down() a semaphore for use with aio.
+ * Returns zero if we acquired it, -EIOCBRETRY if the operation was
+ * queued and the iocb will receive a kick_iocb() on completion.
+ */
+static inline long aio_down(struct kiocb *iocb, struct semaphore * sem)
+{
+ long result;
+
+ __asm__ __volatile__(
+ "# atomic aio_down operation\n\t"
+ LOCK "decl %1\n\t" /* --sem->count */
+ "js 2f\n\t"
+ "movq %3,%2\n" /* sem->aio_owner = iocb */
+ "xorq %0,%0\n\t"
+ "1:\n"
+ LOCK_SECTION_START("")
+ "2:\tcall __aio_down_failed\n\t"
+ "jmp 1b\n"
+ LOCK_SECTION_END
+ :"=a" (result), "+m" (sem->count), "=m" (sem->aio_owner)
+ : "D" (iocb), "S" (sem)
+ :"memory");
+ return result;
+}
+
+/*
* Non-blockingly attempt to down() a semaphore.
* Returns zero if we acquired it
*/
@@ -192,5 +224,15 @@ static inline void up(struct semaphore *
:"D" (sem)
:"memory");
}
+
+static inline void aio_up(struct kiocb *iocb, struct semaphore *sem)
+{
+#ifdef CONFIG_DEBUG_KERNEL
+ BUG_ON(sem->aio_owner != iocb);
+#endif
+ sem->aio_owner = NULL;
+ up(sem);
+}
+
#endif /* __KERNEL__ */
#endif
diff -purN 10_wait_private/mm/filemap.c aio_down-rc6.diff/mm/filemap.c
--- 10_wait_private/mm/filemap.c 2005-06-13 02:08:03.000000000 -0400
+++ aio_down-rc6.diff/mm/filemap.c 2005-06-14 17:22:10.530380544 -0400
@@ -2208,10 +2208,12 @@ ssize_t generic_file_aio_write(struct ki
BUG_ON(iocb->ki_pos != pos);
- down(&inode->i_sem);
+ ret = aio_down(iocb, &inode->i_sem);
+ if (ret)
+ return ret;
ret = __generic_file_aio_write_nolock(iocb, &local_iov, 1,
&iocb->ki_pos);
- up(&inode->i_sem);
+ aio_up(iocb, &inode->i_sem);
if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
ssize_t err;
-
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