linux-kernel - [PATCH] f2fs: remove circular locking between sb_internal and fs

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Message-Id: <20211014190503.717830-1-daeho43@gmail.com>
Date:   Thu, 14 Oct 2021 12:05:03 -0700
From:   Daeho Jeong <daeho43@...il.com>
To:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com
Cc:     Daeho Jeong <daehojeong@...gle.com>
Subject: [PATCH] f2fs: remove circular locking between sb_internal and fs_reclaim

From: Daeho Jeong <daehojeong@...gle.com>

We detected the below circular locking dependency between sb_internal
and fs_reclaim. So, removed it by calling dquot_initialize() before
sb_start_intwrite().

 ======================================================
 WARNING: possible circular locking dependency detected
 ------------------------------------------------------
 kswapd0/133 is trying to acquire lock:
ffffff80d5fb9680 (sb_internal#2){.+.+}-{0:0}, at: evict+0xd4/0x2f8

but task is already holding lock:
ffffffda597c93a8 (fs_reclaim){+.+.}-{0:0}, at:
__fs_reclaim_acquire+0x4/0x50

which lock already depends on the new lock.
...
other info that might help us debug this:

 Chain exists of:

sb_internal#2 --> &s->s_dquot.dqio_sem --> fs_reclaim

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(fs_reclaim);
                                lock(&s->s_dquot.dqio_sem);
                                lock(fs_reclaim);
   lock(sb_internal#2);

Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
---
 fs/f2fs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 86eeb019cc52..a133932333c5 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1370,6 +1370,8 @@ static int f2fs_drop_inode(struct inode *inode)
 			/* should remain fi->extent_tree for writepage */
 			f2fs_destroy_extent_node(inode);
 
+			dquot_initialize(inode);
+
 			sb_start_intwrite(inode->i_sb);
 			f2fs_i_size_write(inode, 0);
 
-- 
2.33.0.1079.g6e70778dc9-goog