Commit 8619f979 authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman
Browse files

sysfs: slim down sysfs_dirent->s_active 



Make sysfs_dirent->s_active an atomic_t instead of rwsem.  This
reduces the size of sysfs_dirent from 136 to 104 on 64bit and from 76
to 60 on 32bit with lock debugging turned off.  With lock debugging
turned on the reduction is much larger.

s_active starts at zero and each active reference increments s_active.
Putting a reference decrements s_active.  Deactivation subtracts
SD_DEACTIVATED_BIAS which is currently INT_MIN and assumed to be small
enough to make s_active negative.  If s_active is negative,
sysfs_get() no longer grants new references.  Deactivation succeeds
immediately if there is no active user; otherwise, it waits using a
completion for the last put.

Due to the removal of lockdep tricks, this change makes things less
trickier in release_sysfs_dirent().  As all the complexity is
contained in three s_active functions, I think it's more readable this
way.

Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent b6b4a439

fs/sysfs/dir.c

+48 −26
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/kobject.h>

#include <linux/namei.h>

#include <linux/idr.h>

#include <linux/completion.h>

#include <asm/semaphore.h>

#include "sysfs.h"
@@ -32,11 +33,24 @@ static DEFINE_IDA(sysfs_ino_ida); 
 */

struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)

{

	if (sd) {

		if (unlikely(!down_read_trylock(&sd->s_active)))

			sd = NULL;

	}

	if (unlikely(!sd))

		return NULL;



	while (1) {

		int v, t;



		v = atomic_read(&sd->s_active);

		if (unlikely(v < 0))

			return NULL;



		t = atomic_cmpxchg(&sd->s_active, v, v + 1);

		if (likely(t == v))

			return sd;

		if (t < 0)

			return NULL;



		cpu_relax();

	}

}



/**
@@ -48,8 +62,21 @@ struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd) 
 */

void sysfs_put_active(struct sysfs_dirent *sd)

{

	if (sd)

		up_read(&sd->s_active);

	struct completion *cmpl;

	int v;



	if (unlikely(!sd))

		return;



	v = atomic_dec_return(&sd->s_active);

	if (likely(v != SD_DEACTIVATED_BIAS))

		return;



	/* atomic_dec_return() is a mb(), we'll always see the updated

	 * sd->s_sibling.next.

	 */

	cmpl = (void *)sd->s_sibling.next;

	complete(cmpl);

}



/**
@@ -95,17 +122,25 @@ void sysfs_put_active_two(struct sysfs_dirent *sd) 
 *	sysfs_deactivate - deactivate sysfs_dirent

 *	@sd: sysfs_dirent to deactivate

 *

 *	Deny new active references and drain existing ones.  s_active

 *	will be unlocked when the sysfs_dirent is released.

 *	Deny new active references and drain existing ones.

 */

void sysfs_deactivate(struct sysfs_dirent *sd)

{

	down_write_nested(&sd->s_active, SYSFS_S_ACTIVE_DEACTIVATE);

	DECLARE_COMPLETION_ONSTACK(wait);

	int v;



	BUG_ON(!list_empty(&sd->s_sibling));

	sd->s_sibling.next = (void *)&wait;



	/* s_active will be unlocked by the thread doing the final put

	 * on @sd.  Lie to lockdep.

	/* atomic_add_return() is a mb(), put_active() will always see

	 * the updated sd->s_sibling.next.

	 */

	rwsem_release(&sd->s_active.dep_map, 1, _RET_IP_);

	v = atomic_add_return(SD_DEACTIVATED_BIAS, &sd->s_active);



	if (v != SD_DEACTIVATED_BIAS)

		wait_for_completion(&wait);



	INIT_LIST_HEAD(&sd->s_sibling);

}



static int sysfs_alloc_ino(ino_t *pino)
@@ -141,19 +176,6 @@ void release_sysfs_dirent(struct sysfs_dirent * sd) 
 repeat:

	parent_sd = sd->s_parent;



	/* If @sd is being released after deletion, s_active is write

	 * locked.  If @sd is cursor for directory walk or being

	 * released prematurely, s_active has no reader or writer.

	 *

	 * sysfs_deactivate() lies to lockdep that s_active is

	 * unlocked immediately.  Lie one more time to cover the

	 * previous lie.

	 */

	if (!down_write_trylock(&sd->s_active))

		rwsem_acquire(&sd->s_active.dep_map,

			      SYSFS_S_ACTIVE_DEACTIVATE, 0, _RET_IP_);

	up_write(&sd->s_active);



	if (sd->s_type & SYSFS_KOBJ_LINK)

		sysfs_put(sd->s_elem.symlink.target_sd);

	if (sd->s_type & SYSFS_COPY_NAME)
@@ -213,8 +235,8 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type) 
		goto err_out;



	atomic_set(&sd->s_count, 1);

	atomic_set(&sd->s_active, 0);

	atomic_set(&sd->s_event, 1);

	init_rwsem(&sd->s_active);

	INIT_LIST_HEAD(&sd->s_children);

	INIT_LIST_HEAD(&sd->s_sibling);

fs/sysfs/sysfs.h

+2 −11
Original line number Diff line number Diff line
@@ -21,7 +21,7 @@ struct sysfs_elem_bin_attr { 
 */

struct sysfs_dirent {

	atomic_t		s_count;

	struct rw_semaphore	s_active;

	atomic_t		s_active;

	struct sysfs_dirent	* s_parent;

	struct list_head	s_sibling;

	struct list_head	s_children;
@@ -42,16 +42,7 @@ struct sysfs_dirent { 
	atomic_t		s_event;

};



/*

 * A sysfs file which deletes another file when written to need to

 * write lock the s_active of the victim while its s_active is read

 * locked for the write operation.  Tell lockdep that this is okay.

 */

enum sysfs_s_active_class

{

	SYSFS_S_ACTIVE_NORMAL,		/* file r/w access, etc - default */

	SYSFS_S_ACTIVE_DEACTIVATE,	/* file deactivation */

};

#define SD_DEACTIVATED_BIAS	INT_MIN



extern struct vfsmount * sysfs_mount;

extern struct kmem_cache *sysfs_dir_cachep;

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