Quoted from Jing Xia's report, there is a potential deadlock may happen
between kworker and checkpoint as below:
[T:writeback] [T:checkpoint]
- wb_writeback
- blk_start_plug
bio contains NodeA was plugged in writeback threads
- do_writepages -- sync write inodeB,
inc wb_sync_req[DATA]
- f2fs_write_data_pages
- f2fs_write_single_data_page --
write last dirty page
- f2fs_do_write_data_page
- set_page_writeback -- clear page
dirty flag and
PAGECACHE_TAG_DIRTY tag in radix
tree
- f2fs_outplace_write_data
- f2fs_update_data_blkaddr
- f2fs_wait_on_page_writeback --
wait NodeA to writeback here
- inode_dec_dirty_pages
- writeback_sb_inodes
- writeback_single_inode
- do_writepages
- f2fs_write_data_pages -- skip writepages due to wb_sync_req[DATA]
- wbc->pages_skipped += get_dirty_pages() -- PAGECACHE_TAG_DIRTY is not
set but get_dirty_pages() returns one
- requeue_inode -- requeue inode to wb->b_dirty queue due to
non-zero.pages_skipped
- blk_finish_plug
Let's try to avoid deadlock condition by forcing unplugging previous bio via
blk_finish_plug(current->plug) once we'v skipped writeback in writepages()
due to valid sbi->wb_sync_req[DATA/NODE].
Fixes: 687de7f1010c ("f2fs: avoid IO split due to mixed WB_SYNC_ALL and
WB_SYNC_NONE")
Signed-off-by: Zhiguo Niu <[email protected]>
Signed-off-by: Jing Xia <[email protected]>
Signed-off-by: Chao Yu <[email protected]>
---
fs/f2fs/data.c | 6 +++++-
fs/f2fs/node.c | 6 +++++-
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 76d6fe7b0c8f..932a4c81acaf 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3174,8 +3174,12 @@ static int __f2fs_write_data_pages(struct address_space
*mapping,
/* to avoid spliting IOs due to mixed WB_SYNC_ALL and WB_SYNC_NONE */
if (wbc->sync_mode == WB_SYNC_ALL)
atomic_inc(&sbi->wb_sync_req[DATA]);
- else if (atomic_read(&sbi->wb_sync_req[DATA]))
+ else if (atomic_read(&sbi->wb_sync_req[DATA])) {
+ /* to avoid potential deadlock */
+ if (current->plug)
+ blk_finish_plug(current->plug);
goto skip_write;
+ }
if (__should_serialize_io(inode, wbc)) {
mutex_lock(&sbi->writepages);
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 556fcd8457f3..69c6bcaf5aae 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -2106,8 +2106,12 @@ static int f2fs_write_node_pages(struct address_space
*mapping,
if (wbc->sync_mode == WB_SYNC_ALL)
atomic_inc(&sbi->wb_sync_req[NODE]);
- else if (atomic_read(&sbi->wb_sync_req[NODE]))
+ else if (atomic_read(&sbi->wb_sync_req[NODE])) {
+ /* to avoid potential deadlock */
+ if (current->plug)
+ blk_finish_plug(current->plug);
goto skip_write;
+ }
trace_f2fs_writepages(mapping->host, wbc, NODE);
--
2.32.0
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