Re: [RFC] aio_down() for i386 and x86_64

[Suparna Bhattacharya]

On Tue, Jun 14, 2005 at 05:50:22PM -0400, Benjamin LaHaise wrote:
> 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.

Interesting approach - using ki_wait.private for this.
Could we make aio_down take a wait queue parameter as well instead of
the iocb ?

Need to think a little about impact on io cancellation.

BTW, is the duplication of functions across architectures still needed ? I
thought that one of advantages of implementing a separate aio_down
routine vs modifiying down to become retryable was to get away from
that ... or wasn't it ?

Meanwhile, I probably need to repost my aio_wait_bit patches - there
may be some impact here.

Regards
Suparna

> 
> 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;
> --
> To unsubscribe, send a message with 'unsubscribe linux-aio' in
> the body to majordomo@xxxxxxxxxx  For more info on Linux AIO,
> see: http://www.kvack.org/aio/
> Don't email: <a href=mailto:"aart@xxxxxxxxx";>aart@xxxxxxxxx</a>

-- 
Suparna Bhattacharya (suparna@xxxxxxxxxx)
Linux Technology Center
IBM Software Lab, India

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