[PATCH 66/75] sysfs: move sysfs file poll implementation to sysfs_open_dirent

Greg Kroah-Hartman
2007-10-12T22:57:13Z

From: Tejun Heo <htejun@gmail.com>

Sysfs file poll implementation is scattered over sysfs and kobject.
Event numbering is done in sysfs_dirent but wait itself is done on
kobject. This not only unecessarily bloats both kobject and
sysfs_dirent but is also buggy - if a sysfs_dirent is removed while
there still are pollers, the associaton betwen the kobject and
sysfs_dirent breaks and kobject may be freed with the pollers still
sleeping on it.

This patch moves whole poll implementation into sysfs_open_dirent.
Each time a sysfs_open_dirent is created, event number restarts from 1
and pollers sleep on sysfs_open_dirent. As event sequence number is
meaningless without any open file and pollers should have open file
and thus sysfs_open_dirent, this ephemeral event counting works and is
a saner implementation.

This patch fixes the dnagling sleepers bug and reduces the sizes of
kobject and sysfs_dirent by one pointer.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/sysfs/dir.c | 1 -
fs/sysfs/file.c | 25 +++++++++++++++++++------
fs/sysfs/sysfs.h | 1 -
include/linux/kobject.h | 1 -
lib/kobject.c | 1 -
5 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 4ad9422..e301a12 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -318,7 +318,6 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)

atomic_set(&sd->s_count, 1);
atomic_set(&sd->s_active, 0);
- atomic_set(&sd->s_event, 1);

sd->s_name = name;
sd->s_mode = mode;
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index b13ba94..c05f961 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -62,6 +62,8 @@ static spinlock_t sysfs_open_dirent_lock = SPIN_LOCK_UNLOCKED;

struct sysfs_open_dirent {
atomic_t refcnt;
+ atomic_t event;
+ wait_queue_head_t poll;
struct list_head buffers; /* goes through sysfs_buffer.list */
};

@@ -104,7 +106,7 @@ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer
if (!sysfs_get_active_two(attr_sd))
return -ENODEV;

- buffer->event = atomic_read(&attr_sd->s_event);
+ buffer->event = atomic_read(&attr_sd->s_attr.open->event);
count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);

sysfs_put_active_two(attr_sd);
@@ -301,6 +303,8 @@ static int sysfs_get_open_dirent(struct sysfs_dirent *sd,
return -ENOMEM;

atomic_set(&new_od->refcnt, 0);
+ atomic_set(&new_od->event, 1);
+ init_waitqueue_head(&new_od->poll);
INIT_LIST_HEAD(&new_od->buffers);
goto retry;
}
@@ -443,17 +447,17 @@ static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
{
struct sysfs_buffer * buffer = filp->private_data;
struct sysfs_dirent *attr_sd = filp->f_path.dentry->d_fsdata;
- struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
+ struct sysfs_open_dirent *od = attr_sd->s_attr.open;

/* need parent for the kobj, grab both */
if (!sysfs_get_active_two(attr_sd))
goto trigger;

- poll_wait(filp, &kobj->poll, wait);
+ poll_wait(filp, &od->poll, wait);

sysfs_put_active_two(attr_sd);

- if (buffer->event != atomic_read(&attr_sd->s_event))
+ if (buffer->event != atomic_read(&od->event))
goto trigger;

return 0;
@@ -474,8 +478,17 @@ void sysfs_notify(struct kobject *k, char *dir, char *attr)
if (sd && attr)
sd = sysfs_find_dirent(sd, attr);
if (sd) {
- atomic_inc(&sd->s_event);
- wake_up_interruptible(&k->poll);
+ struct sysfs_open_dirent *od;
+
+ spin_lock(&sysfs_open_dirent_lock);
+
+ od = sd->s_attr.open;
+ if (od) {
+ atomic_inc(&od->event);
+ wake_up_interruptible(&od->poll);
+ }
+
+ spin_unlock(&sysfs_open_dirent_lock);
}

mutex_unlock(&sysfs_mutex);
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 3adce7d..269c845 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -46,7 +46,6 @@ struct sysfs_dirent {
ino_t s_ino;
umode_t s_mode;
struct iattr *s_iattr;
- atomic_t s_event;
};

#define SD_DEACTIVATED_BIAS INT_MIN
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 0777b3f..a8a84fc 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -66,7 +66,6 @@ struct kobject {
struct kset * kset;
struct kobj_type * ktype;
struct sysfs_dirent * sd;
- wait_queue_head_t poll;
};

extern int kobject_set_name(struct kobject *, const char *, ...)
diff --git a/lib/kobject.c b/lib/kobject.c
index e8181d3..fc6db6b 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -131,7 +131,6 @@ void kobject_init(struct kobject * kobj)
return;
kref_init(&kobj->kref);
INIT_LIST_HEAD(&kobj->entry);
- init_waitqueue_head(&kobj->poll);
kobj->kset = kset_get(kobj->kset);
}

--
1.5.3.4