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

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Message-Id: <20201109170012.2129411-1-jaegeuk@kernel.org>
Date:   Mon,  9 Nov 2020 09:00:12 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>,
        Light Hsieh <Light.Hsieh@...iatek.com>
Subject: [PATCH] f2fs: avoid race condition for shinker count

Light reported sometimes shinker gets nat_cnt < dirty_nat_cnt resulting in
wrong do_shinker work. Basically the two counts should not happen like that.

So, I suspect this race condtion where:
- f2fs_try_to_free_nats            __flush_nat_entry_set
 nat_cnt=2, dirty_nat_cnt=2
                                   __clear_nat_cache_dirty
                                    spin_lock(nat_list_lock)
                                    list_move()
                                    spin_unlock(nat_list_lock)
 spin_lock(nat_list_lock)
 list_del()
 spin_unlock(nat_list_lock)
 nat_cnt=1, dirty_nat_cnt=2
                                   nat_cnt=1, dirty_nat_cnt=1

Reported-by: Light Hsieh <Light.Hsieh@...iatek.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 fs/f2fs/node.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 42394de6c7eb..e8ec65e40f06 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -269,11 +269,10 @@ static void __clear_nat_cache_dirty(struct f2fs_nm_info *nm_i,
 {
 	spin_lock(&nm_i->nat_list_lock);
 	list_move_tail(&ne->list, &nm_i->nat_entries);
-	spin_unlock(&nm_i->nat_list_lock);
-
 	set_nat_flag(ne, IS_DIRTY, false);
 	set->entry_cnt--;
 	nm_i->dirty_nat_cnt--;
+	spin_unlock(&nm_i->nat_list_lock);
 }
 
 static unsigned int __gang_lookup_nat_set(struct f2fs_nm_info *nm_i,
-- 
2.29.2.222.g5d2a92d10f8-goog