sysfs: move sysfs file poll implementation to sysfs_open_dirent

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>

1 files changed, 19 insertions, 6 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index b13ba94cf8ac..c05f9618b2dc 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);