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authorOleg Nesterov <oleg@redhat.com>2016-09-26 18:07:48 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-10-28 03:01:32 -0400
commit2f634e1322f7e1ca0973a606cb24f5f669884359 (patch)
tree519a290265833ceff0a6c685427eb6b7d1ab90c6 /fs/super.c
parent8cffabab018cad0dfcfe3ab44ff8c2510fc2408d (diff)
fs/super.c: fix race between freeze_super() and thaw_super()
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@kyup.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/super.c')
-rw-r--r--fs/super.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/fs/super.c b/fs/super.c
index f5f4b328f860..d4d2591b77c8 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1326,8 +1326,8 @@ 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);
@@ -1346,7 +1346,7 @@ 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;
}