sysfs: Support sysfs_notify from atomic context with new sysfs_notify_dirent

Support sysfs_notify from atomic context with new sysfs_notify_dirent

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: Neil Brown <neilb@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index a5db496f71c..93c6d6b27c4 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -124,7 +124,7 @@ 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)
+static inline struct sysfs_dirent *__sysfs_get(struct sysfs_dirent *sd)
 {
 	if (sd) {
 		WARN_ON(!atomic_read(&sd->s_count));
@@ -132,12 +132,14 @@ static inline struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
 	}
 	return sd;
 }
+#define sysfs_get(sd) __sysfs_get(sd)
 
-static inline void sysfs_put(struct sysfs_dirent *sd)
+static inline void __sysfs_put(struct sysfs_dirent *sd)
 {
 	if (sd && atomic_dec_and_test(&sd->s_count))
 		release_sysfs_dirent(sd);
 }
+#define sysfs_put(sd) __sysfs_put(sd)
 
 /*
  * inode.c