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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>
This commit is contained in:
Chao Yu 2017-08-31 18:56:05 +08:00 committed by Jaegeuk Kim
parent 025d63a486
commit edd748e6c8
1 changed files with 1 additions and 3 deletions
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4
fs/f2fs/segment.c
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@ -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 */