linux-kernel - Re: [PATCH v2] f2fs: avoid race condition for shinker count

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Message-ID: <20201112053414.GB3826485@google.com>
Date:   Wed, 11 Nov 2020 21:34:14 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com
Cc:     Light Hsieh <Light.Hsieh@...iatek.com>
Subject: Re: [PATCH v2] f2fs: avoid race condition for shinker count

Light reported sometimes shinker gets nat_cnt < dirty_nat_cnt resulting in
wrong do_shinker work. Let's avoid to get stale data by using nat_tree_lock.

Reported-by: Light Hsieh <Light.Hsieh@...iatek.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 fs/f2fs/shrinker.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/shrinker.c b/fs/f2fs/shrinker.c
index d66de5999a26..d42245ab07f4 100644
--- a/fs/f2fs/shrinker.c
+++ b/fs/f2fs/shrinker.c
@@ -18,7 +18,11 @@ static unsigned int shrinker_run_no;
 
 static unsigned long __count_nat_entries(struct f2fs_sb_info *sbi)
 {
-	long count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt;
+	long count;
+
+	down_read(&nm_i->nat_tree_lock);
+	count = NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt;
+	up_read(&nm_i->nat_tree_lock);
 
 	return count > 0 ? count : 0;
 }
-- 
2.29.2.299.gdc1121823c-goog