[RFC PATCH 1/2] ext4: fix fast commit inode enqueueing during a full journal commit

Luis Henriques (SUSE)
2024-05-21T15:45:44Z

When a full journal commit is on-going, any fast commit has to be enqueued
into a different queue: FC_Q_STAGING instead of FC_Q_MAIN. This enqueueing
is done only once, i.e. if an inode is already queued in a previous fast
commit entry it won't be enqueued again. However, if a full commit starts
_after_ the inode is enqueued into FC_Q_MAIN, the next fast commit needs to
be done into FC_Q_STAGING. And this is not being done in function
ext4_fc_track_template().

This patch fixes the issue by simply re-enqueuing the inode from the MAIN
into the STAGING queue.

This bug was found using fstest generic/047. This test creates several 32k
bytes files, sync'ing each of them after it's creation, and then shutting
down the filesystem. Some data may be loss in this operation; for example a
file may have it's size truncated to zero.

Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev>
---
fs/ext4/fast_commit.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 87c009e0c59a..337b5289cf11 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -396,12 +396,19 @@ static int ext4_fc_track_template(
return ret;

spin_lock(&sbi->s_fc_lock);
- if (list_empty(&EXT4_I(inode)->i_fc_list))
- list_add_tail(&EXT4_I(inode)->i_fc_list,
- (sbi->s_journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
- sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING) ?
- &sbi->s_fc_q[FC_Q_STAGING] :
- &sbi->s_fc_q[FC_Q_MAIN]);
+ if (sbi->s_journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
+ sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING) {
+ if (list_empty(&EXT4_I(inode)->i_fc_list))
+ list_add_tail(&EXT4_I(inode)->i_fc_list,
+ &sbi->s_fc_q[FC_Q_STAGING]);
+ else
+ list_move_tail(&EXT4_I(inode)->i_fc_list,
+ &sbi->s_fc_q[FC_Q_STAGING]);
+ } else {
+ if (list_empty(&EXT4_I(inode)->i_fc_list))
+ list_add_tail(&EXT4_I(inode)->i_fc_list,
+ &sbi->s_fc_q[FC_Q_MAIN]);
+ }
spin_unlock(&sbi->s_fc_lock);

return ret;