From edd748e6c8e824a8281f8a8450f12c4a95ec61ee Mon Sep 17 00:00:00 2001 From: Chao Yu Date: Thu, 31 Aug 2017 18:56:05 +0800 Subject: [PATCH] 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 Signed-off-by: Jaegeuk Kim --- fs/f2fs/segment.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index d6c3f456ea51..1215ca1bd4e2 100644 --- a/fs/f2fs/segment.c +++ b/fs/f2fs/segment.c @@ -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 */