fs: Skip atime update on frozen filesystem

It is unexpected to block reading of frozen filesystem because of atime update.
Also handling blocking on frozen filesystem because of atime update would make
locking more complex than it already is. So just skip atime update when
filesystem is frozen like we skip it when filesystem is remounted read-only.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 006c85ca06eb..74d7c20fac88 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1542,9 +1542,11 @@ void touch_atime(struct path *path)
         if (timespec_equal(&inode->i_atime, &now))
                 return;
 
-        if (mnt_want_write(mnt))
+        if (!sb_start_write_trylock(inode->i_sb))
                 return;
 
+        if (__mnt_want_write(mnt))
+                goto skip_update;
         /*
          * File systems can error out when updating inodes if they need to
          * allocate new space to modify an inode (such is the case for
@@ -1553,7 +1555,9 @@ void touch_atime(struct path *path)
          * so just ignore the return value.
          */
         update_time(inode, &now, S_ATIME);
-        mnt_drop_write(mnt);
+        __mnt_drop_write(mnt);
+skip_update:
+        sb_end_write(inode->i_sb);
 }
 EXPORT_SYMBOL(touch_atime);