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SubjectRe: [PATCH 2/2] quota: fix warning in dqgrab()
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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
>>

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