[PATCH 5.17 0282/1126] f2fs: fix to avoid potential deadlock

Greg Kroah-Hartman
2022-04-05T08:19:17Z

From: Chao Yu <chao@kernel.org>

[ Upstream commit 344150999b7fc88502a65bbb147a47503eca2033 ]

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 <zhiguo.niu@unisoc.com>
Signed-off-by: Jing Xia <jing.xia@unisoc.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 8c417864c66a..e1ef925be60c 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3163,8 +3163,12 @@ 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 50b2874e758c..4ff7dfb54250 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -2111,8 +2111,12 @@ 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);

--
2.34.1