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f2fs: fix to avoid potential deadlock

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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: 687de7f101 ("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>
This commit is contained in:
Chao Yu 2022-01-27 13:44:49 +08:00 committed by Jaegeuk Kim
parent 680af5b824
commit 344150999b
2 changed files with 10 additions and 2 deletions
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6
fs/f2fs/data.c
View File

@ -3169,8 +3169,12 @@ 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);

6
fs/f2fs/node.c
View File

@ -2112,8 +2112,12 @@ 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);