This is a note to let you know that I've just added the patch titled
fs/super.c: fix race between freeze_super() and thaw_super()
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fs-super.c-fix-race-between-freeze_super-and-thaw_super.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 89f39af129382a40d7cd1f6914617282cfeee28e Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Date: Mon, 26 Sep 2016 18:07:48 +0200
Subject: fs/super.c: fix race between freeze_super() and thaw_super()
From: Oleg Nesterov <oleg@xxxxxxxxxx>
commit 89f39af129382a40d7cd1f6914617282cfeee28e upstream.
Change thaw_super() to check frozen != SB_FREEZE_COMPLETE rather than
frozen == SB_UNFROZEN, otherwise it can race with freeze_super() which
drops sb->s_umount after SB_FREEZE_WRITE to preserve the lock ordering.
In this case thaw_super() will wrongly call s_op->unfreeze_fs() before
it was actually frozen, and call sb_freeze_unlock() which leads to the
unbalanced percpu_up_write(). Unfortunately lockdep can't detect this,
so this triggers misc BUG_ON()'s in kernel/rcu/sync.c.
Reported-and-tested-by: Nikolay Borisov <kernel@xxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/super.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/fs/super.c
+++ b/fs/super.c
@@ -1346,8 +1346,8 @@ int freeze_super(struct super_block *sb)
}
}
/*
- * This is just for debugging purposes so that fs can warn if it
- * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
+ * For debugging purposes so that fs can warn if it sees write activity
+ * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().
*/
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
up_write(&sb->s_umount);
@@ -1366,7 +1366,7 @@ int thaw_super(struct super_block *sb)
int error;
down_write(&sb->s_umount);
- if (sb->s_writers.frozen == SB_UNFROZEN) {
+ if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) {
up_write(&sb->s_umount);
return -EINVAL;
}
Patches currently in stable-queue which might be from oleg@xxxxxxxxxx are
queue-3.18/fs-super.c-fix-race-between-freeze_super-and-thaw_super.patch