This is a note to let you know that I've just added the patch titled
fs-writeback: do not requeue a clean inode having skipped pages
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fs-writeback-do-not-requeue-a-clean-inode-having-ski.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 91fd6d0b1a881061fa737b9afd5f1a4714d326c1
Author: Chunhai Guo <guochunhai@xxxxxxxx>
Date: Fri Sep 15 22:51:31 2023 -0600
fs-writeback: do not requeue a clean inode having skipped pages
[ Upstream commit be049c3a088d512187407b7fd036cecfab46d565 ]
When writing back an inode and performing an fsync on it concurrently, a
deadlock issue may arise as shown below. In each writeback iteration, a
clean inode is requeued to the wb->b_dirty queue due to non-zero
pages_skipped, without anything actually being written. This causes an
infinite loop and prevents the plug from being flushed, resulting in a
deadlock. We now avoid requeuing the clean inode to prevent this issue.
wb_writeback fsync (inode-Y)
blk_start_plug(&plug)
for (;;) {
iter i-1: some reqs with page-X added into plug->mq_list // f2fs node page-X with PG_writeback
filemap_fdatawrite
__filemap_fdatawrite_range // write inode-Y with sync_mode WB_SYNC_ALL
do_writepages
f2fs_write_data_pages
__f2fs_write_data_pages // wb_sync_req[DATA]++ for WB_SYNC_ALL
f2fs_write_cache_pages
f2fs_write_single_data_page
f2fs_do_write_data_page
f2fs_outplace_write_data
f2fs_update_data_blkaddr
f2fs_wait_on_page_writeback
wait_on_page_writeback // wait for f2fs node page-X
iter i:
progress = __writeback_inodes_wb(wb, work)
. writeback_sb_inodes
. __writeback_single_inode // write inode-Y with sync_mode WB_SYNC_NONE
. . do_writepages
. . f2fs_write_data_pages
. . . __f2fs_write_data_pages // skip writepages due to (wb_sync_req[DATA]>0)
. . . wbc->pages_skipped += get_dirty_pages(inode) // wbc->pages_skipped = 1
. if (!(inode->i_state & I_DIRTY_ALL)) // i_state = I_SYNC | I_SYNC_QUEUED
. total_wrote++; // total_wrote = 1
. requeue_inode // requeue inode-Y to wb->b_dirty queue due to non-zero pages_skipped
if (progress) // progress = 1
continue;
iter i+1:
queue_io
// similar process with iter i, infinite for-loop !
}
blk_finish_plug(&plug) // flush plug won't be called
Signed-off-by: Chunhai Guo <guochunhai@xxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Message-Id: <20230916045131.957929-1-guochunhai@xxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index c76537a6826a7..5f0abea107e46 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1557,10 +1557,15 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
if (wbc->pages_skipped) {
/*
- * writeback is not making progress due to locked
- * buffers. Skip this inode for now.
+ * Writeback is not making progress due to locked buffers.
+ * Skip this inode for now. Although having skipped pages
+ * is odd for clean inodes, it can happen for some
+ * filesystems so handle that gracefully.
*/
- redirty_tail_locked(inode, wb);
+ if (inode->i_state & I_DIRTY_ALL)
+ redirty_tail_locked(inode, wb);
+ else
+ inode_cgwb_move_to_attached(inode, wb);
return;
}
