linux-kernel - [PATCH 2/2] quota: fix warning in dqgrab()

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Date:   Sat, 27 May 2023 09:40:18 +0800
From:   Ye Bin <yebin10@...wei.com>
To:     <jack@...e.com>, <linux-kernel@...r.kernel.org>
CC:     <yebin10@...wei.com>
Subject: [PATCH 2/2] quota: fix warning in dqgrab()

There's issue as follows when do fault injection:
WARNING: CPU: 1 PID: 14870 at include/linux/quotaops.h:51 dquot_disable+0x13b7/0x18c0
Modules linked in:
CPU: 1 PID: 14870 Comm: fsconfig Not tainted 6.3.0-next-20230505-00006-g5107a9c821af-dirty #541
RIP: 0010:dquot_disable+0x13b7/0x18c0
RSP: 0018:ffffc9000acc79e0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88825e41b980
RDX: 0000000000000000 RSI: ffff88825e41b980 RDI: 0000000000000002
RBP: ffff888179f68000 R08: ffffffff82087ca7 R09: 0000000000000000
R10: 0000000000000001 R11: ffffed102f3ed026 R12: ffff888179f68130
R13: ffff888179f68110 R14: dffffc0000000000 R15: ffff888179f68118
FS:  00007f450a073740(0000) GS:ffff88882fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe96f2efd8 CR3: 000000025c8ad000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 dquot_load_quota_sb+0xd53/0x1060
 dquot_resume+0x172/0x230
 ext4_reconfigure+0x1dc6/0x27b0
 reconfigure_super+0x515/0xa90
 __x64_sys_fsconfig+0xb19/0xd20
 do_syscall_64+0x39/0xb0
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Above issue may happens as follows:
ProcessA              ProcessB                    ProcessC
sys_fsconfig
  vfs_fsconfig_locked
   reconfigure_super
     ext4_remount
      dquot_suspend -> suspend all type quota

                 sys_fsconfig
                  vfs_fsconfig_locked
                    reconfigure_super
                     ext4_remount
                      dquot_resume
                       ret = dquot_load_quota_sb
                        add_dquot_ref
                                           do_open  -> open file O_RDWR
                                            vfs_open
                                             do_dentry_open
                                              get_write_access
                                               atomic_inc_unless_negative(&inode->i_writecount)
                                              ext4_file_open
                                               dquot_file_open
                                                dquot_initialize
                                                  __dquot_initialize
                                                   dqget
						    atomic_inc(&dquot->dq_count);

                          __dquot_initialize
                           __dquot_initialize
                            dqget
                             if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
                               ext4_acquire_dquot
			        -> Return error DQ_ACTIVE_B flag isn't set
                         dquot_disable
			  invalidate_dquots
			   if (atomic_read(&dquot->dq_count))
	                    dqgrab
			     WARN_ON_ONCE(!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
	                      -> Trigger warning

In the above scenario, 'dquot->dq_flags' has no DQ_ACTIVE_B is normal when
dqgrab().
So just remove 'WARN_ON_ONCE(!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))'
in dqgrab().

Signed-off-by: Ye Bin <yebin10@...wei.com>
---
 include/linux/quotaops.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
index 11a4becff3a9..cb5e4c11e503 100644
--- a/include/linux/quotaops.h
+++ b/include/linux/quotaops.h
@@ -48,7 +48,6 @@ static inline struct dquot *dqgrab(struct dquot *dquot)
 {
 	/* Make sure someone else has active reference to dquot */
 	WARN_ON_ONCE(!atomic_read(&dquot->dq_count));
-	WARN_ON_ONCE(!test_bit(DQ_ACTIVE_B, &dquot->dq_flags));
 	atomic_inc(&dquot->dq_count);
 	return dquot;
 }
-- 
2.31.1