[PATCH] Support sysfs_notify from atomic context with new sysfs_notify_dirent

[NeilBrown]

sysfs_notify currently takes sysfs_mutex.
This means that it cannot be called in atomic context.
sysfs_mutex  is sometimes held over a malloc (sysfs_rename_dir)
so it can block on low memory.

In md I want to be able to notify on a sysfs attribute from
atomic context, and I don't want to block on low memory because I
could be in the writeout path for freeing memory.

So:
 - export the "sysfs_dirent" structure along with sysfs_get, sysfs_put
   and sysfs_get_dirent so I can get the sysfs_dirent that I want to
   notify on and hold it in an md structure.
 - split sysfs_notify_dirent out of sysfs_notify so the sysfs_dirent
   can be notified on with no blocking (just a spinlock).

Signed-off-by: NeilBrown <neilb@xxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
---
 fs/sysfs/dir.c        |   18 ++++++++++++++++++
 fs/sysfs/file.c       |   31 ++++++++++++++++++-------------
 fs/sysfs/sysfs.h      |   15 ---------------
 include/linux/sysfs.h |   23 +++++++++++++++++++++++
 4 files changed, 59 insertions(+), 28 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 8c0e4b9..09e40a1 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -30,6 +30,23 @@ DEFINE_SPINLOCK(sysfs_assoc_lock);
 static DEFINE_SPINLOCK(sysfs_ino_lock);
 static DEFINE_IDA(sysfs_ino_ida);
 
+struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
+{
+	if (sd) {
+		WARN_ON(!atomic_read(&sd->s_count));
+		atomic_inc(&sd->s_count);
+	}
+	return sd;
+}
+EXPORT_SYMBOL_GPL(sysfs_get);
+
+void sysfs_put(struct sysfs_dirent *sd)
+{
+	if (sd && atomic_dec_and_test(&sd->s_count))
+		release_sysfs_dirent(sd);
+}
+EXPORT_SYMBOL_GPL(sysfs_put);
+
 /**
  *	sysfs_link_sibling - link sysfs_dirent into sibling list
  *	@sd: sysfs_dirent of interest
@@ -606,6 +623,7 @@ struct sysfs_dirent *sysfs_get_dirent(struct sysfs_dirent *parent_sd,
 
 	return sd;
 }
+EXPORT_SYMBOL_GPL(sysfs_get_dirent);
 
 static int create_dir(struct kobject *kobj, struct sysfs_dirent *parent_sd,
 		      const char *name, struct sysfs_dirent **p_sd)
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index e7735f6..c6060e8 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -440,6 +440,22 @@ static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
 	return POLLERR|POLLPRI;
 }
 
+void sysfs_notify_dirent(struct sysfs_dirent *sd)
+{
+	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);
+}
+EXPORT_SYMBOL_GPL(sysfs_notify_dirent);
+
 void sysfs_notify(struct kobject *k, char *dir, char *attr)
 {
 	struct sysfs_dirent *sd = k->sd;
@@ -450,19 +466,8 @@ void sysfs_notify(struct kobject *k, char *dir, char *attr)
 		sd = sysfs_find_dirent(sd, dir);
 	if (sd && attr)
 		sd = sysfs_find_dirent(sd, attr);
-	if (sd) {
-		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);
-	}
+	if (sd)
+		sysfs_notify_dirent(sd);
 
 	mutex_unlock(&sysfs_mutex);
 }
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index ce4e15f..ef5ecc1 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -123,21 +123,6 @@ int sysfs_create_subdir(struct kobject *kobj, const char *name,
 			struct sysfs_dirent **p_sd);
 void sysfs_remove_subdir(struct sysfs_dirent *sd);
 
-static inline struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
-{
-	if (sd) {
-		WARN_ON(!atomic_read(&sd->s_count));
-		atomic_inc(&sd->s_count);
-	}
-	return sd;
-}
-
-static inline void sysfs_put(struct sysfs_dirent *sd)
-{
-	if (sd && atomic_dec_and_test(&sd->s_count))
-		release_sysfs_dirent(sd);
-}
-
 /*
  * inode.c
  */
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 7858eac..3ab58db 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -78,6 +78,8 @@ struct sysfs_ops {
 	ssize_t	(*store)(struct kobject *,struct attribute *,const char *, size_t);
 };
 
+struct sysfs_dirent;
+
 #ifdef CONFIG_SYSFS
 
 int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
@@ -115,6 +117,11 @@ void sysfs_remove_file_from_group(struct kobject *kobj,
 			const struct attribute *attr, const char *group);
 
 void sysfs_notify(struct kobject *kobj, char *dir, char *attr);
+void sysfs_notify_dirent(struct sysfs_dirent *sd);
+struct sysfs_dirent *sysfs_get_dirent(struct sysfs_dirent *parent_sd,
+				      const unsigned char *name);
+struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd);
+void sysfs_put(struct sysfs_dirent *sd);
 
 extern int __must_check sysfs_init(void);
 
@@ -215,6 +222,22 @@ static inline void sysfs_remove_file_from_group(struct kobject *kobj,
 static inline void sysfs_notify(struct kobject *kobj, char *dir, char *attr)
 {
 }
+static inline void sysfs_notify_dirent(struct sysfs_dirent *sd)
+{
+}
+static inline
+struct sysfs_dirent *sysfs_get_dirent(struct sysfs_dirent *parent_sd,
+				      const unsigned char *name)
+{
+	return NULL;
+}
+static inline struct sysfs_dirent sysfs_get(struct sysfs_dirent *sd)
+{
+	return NULL;
+}
+static inline void sysfs_put(struct sysfs_dirent *sd)
+{
+}
 
 static inline int __must_check sysfs_init(void)
 {
-- 
1.5.6.3

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