[PATCH] ext4, jbd2: add REQ_FUA flag when recording an error flag

[Daeho Jeong <daeho.jeong@xxxxxxxxxxx>]

When an error condition is detected, an error status should be recorded into
superblocks of EXT4 or JBD2. However, the write request is submitted now
without REQ_FUA flag, even in "barrier=1" mode, which is followed by
panic() function in "errors=panic" mode. On mobile devices which make
whole system reset as soon as kernel panic occurs, this write request
containing an error flag will disappear just from storage cache without
written to the physical cells. Therefore, when next start, even forever,
the error flag cannot be shown in both superblocks, and e2fsck cannot fix
the filesystem problems automatically, unless e2fsck is executed in
force checking mode.

Signed-off-by: Daeho Jeong <daeho.jeong@xxxxxxxxxxx>
---
 fs/ext4/super.c   |    6 +++++-
 fs/jbd2/journal.c |    2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ca9d4a2..4194328 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4588,6 +4588,7 @@ static int ext4_commit_super(struct super_block *sb, int sync)
 {
  struct ext4_super_block *es = EXT4_SB(sb)->s_es;
  struct buffer_head *sbh = EXT4_SB(sb)->s_sbh;
+ journal_t *journal = EXT4_SB(sb)->s_journal;
  int error = 0;
 
  if (!sbh)
@@ -4638,7 +4639,10 @@ static int ext4_commit_super(struct super_block *sb, int sync)
  ext4_superblock_csum_set(sb);
  mark_buffer_dirty(sbh);
  if (sync) {
-  error = sync_dirty_buffer(sbh);
+  if (journal->j_flags & JBD2_BARRIER)
+   error = __sync_dirty_buffer(sbh, WRITE_FUA);
+  else
+   error = sync_dirty_buffer(sbh);
   if (error)
    return error;
 
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index b96bd80..5b9693d 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1455,7 +1455,7 @@ void jbd2_journal_update_sb_errno(journal_t *journal)
  sb->s_errno    = cpu_to_be32(journal->j_errno);
  read_unlock(&journal->j_state_lock);
 
- jbd2_write_superblock(journal, WRITE_SYNC);
+ jbd2_write_superblock(journal, WRITE_FUA);
 }
 EXPORT_SYMBOL(jbd2_journal_update_sb_errno);
 
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