drop ->s_umount around acct_auto_close()

just repeat the frozen check after regaining it, and check that sb
is still alive.  If several threads hit acct_auto_close() at the
same time, acct_auto_close() will survive that just fine.  And we
really don't want to play with writes and closing the file with
->s_umount held exclusive - it's a deadlock country.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 14 insertions, 4 deletions

diff --git a/fs/super.c b/fs/super.c
index 52ed93eb63df..a369f8964dc1 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -702,12 +702,22 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
                 return -EACCES;
 #endif
 
-        if (flags & MS_RDONLY)
-                acct_auto_close(&sb->s_pins);
-        shrink_dcache_sb(sb);
-
         remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
 
+        if (remount_ro) {
+                if (sb->s_pins.first) {
+                        up_write(&sb->s_umount);
+                        acct_auto_close(&sb->s_pins);
+                        down_write(&sb->s_umount);
+                        if (!sb->s_root)
+                                return 0;
+                        if (sb->s_writers.frozen != SB_UNFROZEN)
+                                return -EBUSY;
+                        remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
+                }
+        }
+        shrink_dcache_sb(sb);
+
         /* If we are remounting RDONLY and current sb is read/write,
            make sure there are no rw files opened */
         if (remount_ro) {