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, 15 insertions, 0 deletions

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 14f0023984d7..ab343e371d64 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -16,6 +16,7 @@
 #include <linux/mount.h>
 #include <linux/pagemap.h>
 #include <linux/init.h>
+#include <linux/module.h>
 
 #include "sysfs.h"
 
@@ -115,3 +116,17 @@ out_err:
 	sysfs_dir_cachep = NULL;
 	goto out;
 }
+
+#undef sysfs_get
+struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
+{
+	return __sysfs_get(sd);
+}
+EXPORT_SYMBOL_GPL(sysfs_get);
+
+#undef sysfs_put
+void sysfs_put(struct sysfs_dirent *sd)
+{
+	__sysfs_put(sd);
+}
+EXPORT_SYMBOL_GPL(sysfs_put);