I am encountering a deadlock issue as shown below. There is a commit
344150999b7f ("f2fs: fix to avoid potential deadlock") can fix this issue.
However, from log analysis, it appears that this is more likely a fake
progress issue similar to commit 68f4c6eba70d ("fs-writeback:
writeback_sb_inodes: Recalculate 'wrote' according skipped pages"). In each
writeback iteration, nothing is written, while writeback_sb_inodes()
increases 'total_wrote' each time, causing an infinite loop. This patch
fixes this issue by not increasing 'total_wrote' when nothing is written.
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>
---
fs/fs-writeback.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 969ce991b0b0..54cdee906be9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1820,6 +1820,7 @@ static long writeback_sb_inodes(struct super_block *sb,
struct inode *inode = wb_inode(wb->b_io.prev);
struct bdi_writeback *tmp_wb;
long wrote;
+ bool is_dirty_before;
if (inode->i_sb != sb) {
if (work->sb) {
@@ -1881,6 +1882,7 @@ static long writeback_sb_inodes(struct super_block *sb,
continue;
}
inode->i_state |= I_SYNC;
+ is_dirty_before = inode->i_state & I_DIRTY_ALL;
wbc_attach_and_unlock_inode(&wbc, inode);
write_chunk = writeback_chunk_size(wb, work);
@@ -1918,7 +1920,7 @@ static long writeback_sb_inodes(struct super_block *sb,
*/
tmp_wb = inode_to_wb_and_lock_list(inode);
spin_lock(&inode->i_lock);
- if (!(inode->i_state & I_DIRTY_ALL))
+ if (!(inode->i_state & I_DIRTY_ALL) && is_dirty_before)
total_wrote++;
requeue_inode(inode, tmp_wb, &wbc);
inode_sync_complete(inode);
--
2.25.1
