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Subject: Re: [PATCH 2/2] quota: fix warning in dqgrab()
To:     Jan Kara <jack@suse.cz>
References: <20230527014018.47396-1-yebin10@huawei.com>
 <20230527014018.47396-3-yebin10@huawei.com>
 <20230530101521.37k7hcjyly2tqj5g@quack3>
CC:     <jack@suse.com>, <linux-kernel@vger.kernel.org>
From:   "yebin (H)" <yebin10@huawei.com>
Message-ID: <647AAC22.9020409@huawei.com>
Date:   Sat, 3 Jun 2023 10:57:38 +0800
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On 2023/5/30 18:15, Jan Kara wrote:
> On Sat 27-05-23 09:40:18, Ye Bin wrote:
>> 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@huawei.com>
> Thanks for the patch! Actually rather than deleting the assertion from
> dqgrab() (which can be and is used by filesystems) I'd replace the dqgrab()
> use in invalidate_dquots() with plain:
>
> 	atomic_inc(&dquot->dq_count);
>
> 								Honza
This is indeed a good idea, I will send a new version.
>> ---
>>   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
>>