[PATCH 5.15.y 2/2] f2fs: fix potential deadlock in gc_merge path of f2fs_balance_fs()

[Sasha Levin <sashal@kernel.org>]

From: Chao Yu <chao@kernel.org>

[ Upstream commit 8b4468ec023d0d1b4669dfb867588997cc03a06b ]

When we mount device w/ gc_merge mount option, we may suffer below
potential deadlock:

Kworker					GC trehad			Truncator
- f2fs_write_cache_pages
 - f2fs_write_single_data_page
  - f2fs_do_write_data_page
   - folio_start_writeback  --- set writeback flag on folio
   - f2fs_outplace_write_data
   : cached folio in internal bio cache
  - f2fs_balance_fs
   - wake_up(gc_thread)
   : wake up gc thread to run foreground GC
   - finish_wait(fggc_wq)
   : wait on the waitqueue --- wait on GC thread to finish the work
									- truncate_inode_pages_range
									 - __filemap_get_folio(, FGP_LOCK)  --- lock folio
									 - truncate_inode_partial_folio
									  - folio_wait_writeback            --- wait on writeback being cleared
					- do_garbage_collect
					 - move_data_page
					  - f2fs_get_lock_data_folio
					   - lock on folio  --- blocked on folio's lock

In order to avoid such deadlock, let's call below functions to commit
cached bios in GC_MERGE path of f2fs_balance_fs() as the same as we did
in NOGC_MERGE path.
- f2fs_submit_merged_write(sbi, DATA);
- f2fs_submit_all_merged_ipu_writes(sbi);

Cc: stable@kernel.org
Fixes: 351df4b20115 ("f2fs: add segment operations")
Cc: Ruipeng Qi <ruipengqi3@gmail.com>
Reported: Sandeep Dhavale <dhavale@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Chao Yu <chaseyu@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/f2fs/segment.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 2e05e899097a91..31b3ff1fa9ba5e 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -515,6 +515,13 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
 	 * dir/node pages without enough free segments.
 	 */
 	if (has_not_enough_free_secs(sbi, 0, 0)) {
+		/*
+		 * Submit all cached OPU/IPU DATA bios before triggering
+		 * foreground GC to avoid potential deadlocks.
+		 */
+		f2fs_submit_merged_write(sbi, DATA);
+		f2fs_submit_all_merged_ipu_writes(sbi);
+
 		if (test_opt(sbi, GC_MERGE) && sbi->gc_thread &&
 					sbi->gc_thread->f2fs_gc_task) {
 			DEFINE_WAIT(wait);
@@ -525,13 +532,6 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
 			io_schedule();
 			finish_wait(&sbi->gc_thread->fggc_wq, &wait);
 		} else {
-			/*
-			 * Submit all cached OPU/IPU DATA bios before triggering
-			 * foreground GC to avoid potential deadlocks.
-			 */
-			f2fs_submit_merged_write(sbi, DATA);
-			f2fs_submit_all_merged_ipu_writes(sbi);
-
 			down_write(&sbi->gc_lock);
 			f2fs_gc(sbi, false, false, false, NULL_SEGNO);
 		}
-- 
2.53.0