ext4: fix races between changing inode journal mode and ext4_writepages

In ext4, there is a race condition between changing inode journal mode
and ext4_writepages(). While ext4_writepages() is executed on a
non-journalled mode inode, the inode's journal mode could be enabled
by ioctl() and then, some pages dirtied after switching the journal
mode will be still exposed to ext4_writepages() in non-journaled mode.
To resolve this problem, we use fs-wide per-cpu rw semaphore by Jan
Kara's suggestion because we don't want to waste ext4_inode_info's
space for this extra rare case.

Signed-off-by: Daeho Jeong <daeho.jeong@samsung.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 304c712dbe12..20c5d52253b4 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -859,6 +859,7 @@ static void ext4_put_super(struct super_block *sb)
         percpu_counter_destroy(&sbi->s_freeinodes_counter);
         percpu_counter_destroy(&sbi->s_dirs_counter);
         percpu_counter_destroy(&sbi->s_dirtyclusters_counter);
+        percpu_free_rwsem(&sbi->s_journal_flag_rwsem);
         brelse(sbi->s_sbh);
 #ifdef CONFIG_QUOTA
         for (i = 0; i < EXT4_MAXQUOTAS; i++)
@@ -3930,6 +3931,9 @@ no_journal:
         if (!err)
                 err = percpu_counter_init(&sbi->s_dirtyclusters_counter, 0,
                                           GFP_KERNEL);
+        if (!err)
+                err = percpu_init_rwsem(&sbi->s_journal_flag_rwsem);
+
         if (err) {
                 ext4_msg(sb, KERN_ERR, "insufficient memory");
                 goto failed_mount6;