f2fs: fix potential deadlock in gc_merge path of f2fs_balance_fs()

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>

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 7c8ac62b1b0d8f3285e2c60f23f0e8f954e83013..1ef4edb770784271181c02adf94fda9d261fe4b4 100644 (file)
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -445,6 +445,13 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
        if (has_enough_free_secs(sbi, 0, 0))
                return;
 
+       /*
+        * 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);
@@ -464,13 +471,6 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
                        .err_gc_skipped = false,
                        .nr_free_secs = 1 };
 
-               /*
-                * 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);
-
                f2fs_down_write_trace(&sbi->gc_lock, &gc_control.lc);
                stat_inc_gc_call_count(sbi, FOREGROUND);
                f2fs_gc(sbi, &gc_control);