Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit edd748e6 authored by Chao Yu's avatar Chao Yu Committed by Jaegeuk Kim
Browse files

f2fs: avoid race in between atomic_read & atomic_inc 



Previously, we will miss merging flush command during fsync due to below
race condition:

Thread A 		Thread B		Thread C
- f2fs_issue_flush
 - atomic_read(&issing_flush)
			- f2fs_issue_flush
			 - atomic_read(&issing_flush)
						- f2fs_issue_flush
						 - atomic_read(&issing_flush)
  - atomic_inc(&issing_flush)
			  - atomic_inc(&issing_flush)
						  - atomic_inc(&issing_flush)
   - submit_flush_wait
			   - submit_flush_wait
						   - submit_flush_wait

It needs to use atomic_inc_return instead to avoid such race.

Signed-off-by: default avatarChao Yu <yuchao0@huawei.com>
Signed-off-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
parent 025d63a4

fs/f2fs/segment.c

+1 −3
Original line number Diff line number Diff line
@@ -536,8 +536,7 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi) 
		return ret;

	}



	if (!atomic_read(&fcc->issing_flush)) {

		atomic_inc(&fcc->issing_flush);

	if (atomic_inc_return(&fcc->issing_flush) == 1) {

		ret = submit_flush_wait(sbi);

		atomic_dec(&fcc->issing_flush);
@@ -547,7 +546,6 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi) 


	init_completion(&cmd.wait);



	atomic_inc(&fcc->issing_flush);

	llist_add(&cmd.llnode, &fcc->issue_list);



	/* update issue_list before we wake up issue_flush thread */