[PATCH 5.14 078/432] f2fs: quota: fix potential deadlock

Greg Kroah-Hartman
2021-09-16T17:17:41Z

From: Chao Yu <chao@kernel.org>

[ Upstream commit 9de71ede81e6d1a111fdd868b2d78d459fa77f80 ]

xfstest generic/587 reports a deadlock issue as below:

======================================================
WARNING: possible circular locking dependency detected
5.14.0-rc1 #69 Not tainted
------------------------------------------------------
repquota/8606 is trying to acquire lock:
ffff888022ac9320 (&sb->s_type->i_mutex_key#18){+.+.}-{3:3}, at: f2fs_quota_sync+0x207/0x300 [f2fs]

but task is already holding lock:
ffff8880084bcde8 (&sbi->quota_sem){.+.+}-{3:3}, at: f2fs_quota_sync+0x59/0x300 [f2fs]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&sbi->quota_sem){.+.+}-{3:3}:
__lock_acquire+0x648/0x10b0
lock_acquire+0x128/0x470
down_read+0x3b/0x2a0
f2fs_quota_sync+0x59/0x300 [f2fs]
f2fs_quota_on+0x48/0x100 [f2fs]
do_quotactl+0x5e3/0xb30
__x64_sys_quotactl+0x23a/0x4e0
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #1 (&sbi->cp_rwsem){++++}-{3:3}:
__lock_acquire+0x648/0x10b0
lock_acquire+0x128/0x470
down_read+0x3b/0x2a0
f2fs_unlink+0x353/0x670 [f2fs]
vfs_unlink+0x1c7/0x380
do_unlinkat+0x413/0x4b0
__x64_sys_unlinkat+0x50/0xb0
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (&sb->s_type->i_mutex_key#18){+.+.}-{3:3}:
check_prev_add+0xdc/0xb30
validate_chain+0xa67/0xb20
__lock_acquire+0x648/0x10b0
lock_acquire+0x128/0x470
down_write+0x39/0xc0
f2fs_quota_sync+0x207/0x300 [f2fs]
do_quotactl+0xaff/0xb30
__x64_sys_quotactl+0x23a/0x4e0
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

Chain exists of:
&sb->s_type->i_mutex_key#18 --> &sbi->cp_rwsem --> &sbi->quota_sem

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&sbi->quota_sem);
lock(&sbi->cp_rwsem);
lock(&sbi->quota_sem);
lock(&sb->s_type->i_mutex_key#18);

*** DEADLOCK ***

3 locks held by repquota/8606:
#0: ffff88801efac0e0 (&type->s_umount_key#53){++++}-{3:3}, at: user_get_super+0xd9/0x190
#1: ffff8880084bc380 (&sbi->cp_rwsem){++++}-{3:3}, at: f2fs_quota_sync+0x3e/0x300 [f2fs]
#2: ffff8880084bcde8 (&sbi->quota_sem){.+.+}-{3:3}, at: f2fs_quota_sync+0x59/0x300 [f2fs]

stack backtrace:
CPU: 6 PID: 8606 Comm: repquota Not tainted 5.14.0-rc1 #69
Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
Call Trace:
dump_stack_lvl+0xce/0x134
dump_stack+0x17/0x20
print_circular_bug.isra.0.cold+0x239/0x253
check_noncircular+0x1be/0x1f0
check_prev_add+0xdc/0xb30
validate_chain+0xa67/0xb20
__lock_acquire+0x648/0x10b0
lock_acquire+0x128/0x470
down_write+0x39/0xc0
f2fs_quota_sync+0x207/0x300 [f2fs]
do_quotactl+0xaff/0xb30
__x64_sys_quotactl+0x23a/0x4e0
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f883b0b4efe

The root cause is ABBA deadlock of inode lock and cp_rwsem,
reorder locks in f2fs_quota_sync() as below to fix this issue:
- lock inode
- lock cp_rwsem
- lock quota_sem

Fixes: db6ec53b7e03 ("f2fs: add a rw_sem to cover quota flag changes")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/super.c | 84 ++++++++++++++++++++++++++++---------------------
1 file changed, 48 insertions(+), 36 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 2f4e4bfb31d3..7cdccb79b378 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2527,6 +2527,33 @@ static int f2fs_enable_quotas(struct super_block *sb)
return 0;
}

+static int f2fs_quota_sync_file(struct f2fs_sb_info *sbi, int type)
+{
+ struct quota_info *dqopt = sb_dqopt(sbi->sb);
+ struct address_space *mapping = dqopt->files[type]->i_mapping;
+ int ret = 0;
+
+ ret = dquot_writeback_dquots(sbi->sb, type);
+ if (ret)
+ goto out;
+
+ ret = filemap_fdatawrite(mapping);
+ if (ret)
+ goto out;
+
+ /* if we are using journalled quota */
+ if (is_journalled_quota(sbi))
+ goto out;
+
+ ret = filemap_fdatawait(mapping);
+
+ truncate_inode_pages(&dqopt->files[type]->i_data, 0);
+out:
+ if (ret)
+ set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
+ return ret;
+}
+
int f2fs_quota_sync(struct super_block *sb, int type)
{
struct f2fs_sb_info *sbi = F2FS_SB(sb);
@@ -2534,57 +2561,42 @@ int f2fs_quota_sync(struct super_block *sb, int type)
int cnt;
int ret;

- /*
- * do_quotactl
- * f2fs_quota_sync
- * down_read(quota_sem)
- * dquot_writeback_dquots()
- * f2fs_dquot_commit
- * block_operation
- * down_read(quota_sem)
- */
- f2fs_lock_op(sbi);
-
- down_read(&sbi->quota_sem);
- ret = dquot_writeback_dquots(sb, type);
- if (ret)
- goto out;
-
/*
* Now when everything is written we can discard the pagecache so
* that userspace sees the changes.
*/
for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
- struct address_space *mapping;

if (type != -1 && cnt != type)
continue;
- if (!sb_has_quota_active(sb, cnt))
- continue;

- mapping = dqopt->files[cnt]->i_mapping;
+ if (!sb_has_quota_active(sb, type))
+ return 0;

- ret = filemap_fdatawrite(mapping);
- if (ret)
- goto out;
+ inode_lock(dqopt->files[cnt]);

- /* if we are using journalled quota */
- if (is_journalled_quota(sbi))
- continue;
+ /*
+ * do_quotactl
+ * f2fs_quota_sync
+ * down_read(quota_sem)
+ * dquot_writeback_dquots()
+ * f2fs_dquot_commit
+ * block_operation
+ * down_read(quota_sem)
+ */
+ f2fs_lock_op(sbi);
+ down_read(&sbi->quota_sem);

- ret = filemap_fdatawait(mapping);
- if (ret)
- set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
+ ret = f2fs_quota_sync_file(sbi, cnt);
+
+ up_read(&sbi->quota_sem);
+ f2fs_unlock_op(sbi);

- inode_lock(dqopt->files[cnt]);
- truncate_inode_pages(&dqopt->files[cnt]->i_data, 0);
inode_unlock(dqopt->files[cnt]);
+
+ if (ret)
+ break;
}
-out:
- if (ret)
- set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
- up_read(&sbi->quota_sem);
- f2fs_unlock_op(sbi);
return ret;
}

--
2.30.2