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, 12 insertions, 3 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 779ef4c11bc1..4d8ebbe00456 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2612,11 +2612,14 @@ static int ext4_writepages(struct address_space *mapping,
         struct blk_plug plug;
         bool give_up_on_write = false;
 
+        percpu_down_read(&sbi->s_journal_flag_rwsem);
         trace_ext4_writepages(inode, wbc);
 
-        if (dax_mapping(mapping))
-                return dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev,
-                                                   wbc);
+        if (dax_mapping(mapping)) {
+                ret = dax_writeback_mapping_range(mapping, inode->i_sb->s_bdev,
+                                                  wbc);
+                goto out_writepages;
+        }
 
         /*
          * No pages to write? This is mainly a kludge to avoid starting
@@ -2786,6 +2789,7 @@ retry:
 out_writepages:
         trace_ext4_writepages_result(inode, wbc, ret,
                                      nr_to_write - wbc->nr_to_write);
+        percpu_up_read(&sbi->s_journal_flag_rwsem);
         return ret;
 }
 
@@ -5436,6 +5440,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
         journal_t *journal;
         handle_t *handle;
         int err;
+        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
         /*
          * We have to be very careful here: changing a data block's
@@ -5475,6 +5480,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
                 }
         }
 
+        percpu_down_write(&sbi->s_journal_flag_rwsem);
         jbd2_journal_lock_updates(journal);
 
         /*
@@ -5491,6 +5497,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
                 err = jbd2_journal_flush(journal);
                 if (err < 0) {
                         jbd2_journal_unlock_updates(journal);
+                        percpu_up_write(&sbi->s_journal_flag_rwsem);
                         ext4_inode_resume_unlocked_dio(inode);
                         return err;
                 }
@@ -5499,6 +5506,8 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
         ext4_set_aops(inode);
 
         jbd2_journal_unlock_updates(journal);
+        percpu_up_write(&sbi->s_journal_flag_rwsem);
+
         if (val)
                 up_write(&EXT4_I(inode)->i_mmap_sem);
         ext4_inode_resume_unlocked_dio(inode);