[PATCH] fs: reintroduce freezing nesting
From: Florian Margaine
Date: Tue Apr 19 2016 - 16:47:36 EST
The behavior was removed inÂ18e9e5104fcd9a973ffe3eed3816c87f2a1b6cd2
noting that this was a better idea than using a counter. However, this
behavior is actually wanted if multiple applications want to freeze
concurrently while remaining non-racy.
This patch reintroduces this feature by using a counter.
---
Âfs/super.cÂÂÂÂÂÂÂÂÂ| 15 +++++++++++----
Âinclude/linux/fs.h |ÂÂ1 +
Â2 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index 74914b1..9fa8ca1 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -231,6 +231,7 @@ static struct super_block *alloc_super(struct
file_system_type *type, int flags)
 Â*/
 down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
 s->s_count = 1;
+ s->s_freezers = 0;
 atomic_set(&s->s_active, 1);
 mutex_init(&s->s_vfs_rename_mutex);
 lockdep_set_class(&s->s_vfs_rename_mutex, &type-
>s_vfs_rename_key);
@@ -1275,12 +1276,12 @@ int freeze_super(struct super_block *sb)
Â{
 int ret;
Â
+ sb->s_freezers++;
+ if (sb->s_writers.frozen != SB_UNFROZEN)
+ return 0;
+
 atomic_inc(&sb->s_active);
 down_write(&sb->s_umount);
- if (sb->s_writers.frozen != SB_UNFROZEN) {
- deactivate_locked_super(sb);
- return -EBUSY;
- }
Â
 if (!(sb->s_flags & MS_BORN)) {
 up_write(&sb->s_umount);
@@ -1338,14 +1339,20 @@ EXPORT_SYMBOL(freeze_super);
 * @sb: the super to thaw
 *
 * Unlocks the filesystem and marks it writeable again after
freeze_super().
+ * Since nesting freezes is allowed, only the last freeze actually
unlocks.
 */
Âint thaw_super(struct super_block *sb)
Â{
 int error;
Â
+ sb->s_freezers--;
+ if (sb->s_freezers > 0)
+ return 0;
+
 down_write(&sb->s_umount);
 if (sb->s_writers.frozen == SB_UNFROZEN) {
 up_write(&sb->s_umount);
+ sb->s_freezers++;
 return -EINVAL;
 }
Â
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e514f76..c045e2a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1333,6 +1333,7 @@ struct super_block {
 struct quota_info s_dquot; /* Diskquota specific
options */
Â
 struct sb_writers s_writers;
+ int s_freezers;
Â
 char s_id[32]; /* Informational
name */
 u8 s_uuid[16]; /* UUID */
--Â
2.8.0