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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: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
hifive-unleashed-5.1
Tejun Heo 2007-06-14 03:45:18 +09:00 committed by Greg Kroah-Hartman
parent b6b4a4399c
commit 8619f97989
2 changed files with 50 additions and 37 deletions
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74
fs/sysfs/dir.c
View File

@ -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();
}
return sd;
}
/**
@ -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;
/* s_active will be unlocked by the thread doing the final put
* on @sd. Lie to lockdep.
BUG_ON(!list_empty(&sd->s_sibling));
sd->s_sibling.next = (void *)&wait;
/* 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);

13
fs/sysfs/sysfs.h
View File

@ -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;