Commit edd748e6 authored Aug 31, 2017 by Chao Yu Committed by Jaegeuk Kim Sep 05, 2017

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: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk 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 */

Admin message