From: Chao Yu Date: Thu, 31 Aug 2017 10:56:05 +0000 (+0800) Subject: f2fs: avoid race in between atomic_read & atomic_inc X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=edd748e6c8e824a8281f8a8450f12c4a95ec61ee;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git 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 --- 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 */