linux-kernel - Re: [PATCH] cgroup/cpuset: fix panic caused by partcmd

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Message-ID: <8281a529-23d6-45a1-85bb-8b7c0a543084@redhat.com>
Date: Mon, 29 Jul 2024 23:48:02 -0400
From: Waiman Long <longman@...hat.com>
To: chenridong <chenridong@...wei.com>, tj@...nel.org,
 lizefan.x@...edance.com, hannes@...xchg.org, adityakali@...gle.com,
 sergeh@...nel.org
Cc: bpf@...r.kernel.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup/cpuset: fix panic caused by partcmd_update

On 7/29/24 23:46, chenridong wrote:
>
>
> On 2024/7/30 11:15, Waiman Long wrote:
>> On 7/29/24 22:55, chenridong wrote:
>>>
>>>
>>> On 2024/7/30 10:34, Waiman Long wrote:
>>>> On 7/29/24 21:53, Chen Ridong wrote:
>>>>> We find a bug as below:
>>>>> BUG: unable to handle page fault for address: 00000003
>>>>> PGD 0 P4D 0
>>>>> Oops: 0000 [#1] PREEMPT SMP NOPTI
>>>>> CPU: 3 PID: 358 Comm: bash Tainted: G        W I 6.6.0-10893-g60d6
>>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
>>>>> 1.15.0-1 04/4
>>>>> RIP: 0010:partition_sched_domains_locked+0x483/0x600
>>>>> Code: 01 48 85 d2 74 0d 48 83 05 29 3f f8 03 01 f3 48 0f bc c2 89 
>>>>> c0 48 9
>>>>> RSP: 0018:ffffc90000fdbc58 EFLAGS: 00000202
>>>>> RAX: 0000000100000003 RBX: ffff888100b3dfa0 RCX: 0000000000000000
>>>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000002fe80
>>>>> RBP: ffff888100b3dfb0 R08: 0000000000000001 R09: 0000000000000000
>>>>> R10: ffffc90000fdbcb0 R11: 0000000000000004 R12: 0000000000000002
>>>>> R13: ffff888100a92b48 R14: 0000000000000000 R15: 0000000000000000
>>>>> FS:  00007f44a5425740(0000) GS:ffff888237d80000(0000) 
>>>>> knlGS:0000000000000
>>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>> CR2: 0000000100030973 CR3: 000000010722c000 CR4: 00000000000006e0
>>>>> Call Trace:
>>>>>   <TASK>
>>>>>   ? show_regs+0x8c/0xa0
>>>>>   ? __die_body+0x23/0xa0
>>>>>   ? __die+0x3a/0x50
>>>>>   ? page_fault_oops+0x1d2/0x5c0
>>>>>   ? partition_sched_domains_locked+0x483/0x600
>>>>>   ? search_module_extables+0x2a/0xb0
>>>>>   ? search_exception_tables+0x67/0x90
>>>>>   ? kernelmode_fixup_or_oops+0x144/0x1b0
>>>>>   ? __bad_area_nosemaphore+0x211/0x360
>>>>>   ? up_read+0x3b/0x50
>>>>>   ? bad_area_nosemaphore+0x1a/0x30
>>>>>   ? exc_page_fault+0x890/0xd90
>>>>>   ? __lock_acquire.constprop.0+0x24f/0x8d0
>>>>>   ? __lock_acquire.constprop.0+0x24f/0x8d0
>>>>>   ? asm_exc_page_fault+0x26/0x30
>>>>>   ? partition_sched_domains_locked+0x483/0x600
>>>>>   ? partition_sched_domains_locked+0xf0/0x600
>>>>>   rebuild_sched_domains_locked+0x806/0xdc0
>>>>>   update_partition_sd_lb+0x118/0x130
>>>>>   cpuset_write_resmask+0xffc/0x1420
>>>>>   cgroup_file_write+0xb2/0x290
>>>>>   kernfs_fop_write_iter+0x194/0x290
>>>>>   new_sync_write+0xeb/0x160
>>>>>   vfs_write+0x16f/0x1d0
>>>>>   ksys_write+0x81/0x180
>>>>>   __x64_sys_write+0x21/0x30
>>>>>   x64_sys_call+0x2f25/0x4630
>>>>>   do_syscall_64+0x44/0xb0
>>>>>   entry_SYSCALL_64_after_hwframe+0x78/0xe2
>>>>> RIP: 0033:0x7f44a553c887
>>>>>
>>>>> It can be reproduced with cammands:
>>>>> cd /sys/fs/cgroup/
>>>>> mkdir test
>>>>> cd test/
>>>>> echo +cpuset > ../cgroup.subtree_control
>>>>> echo root > cpuset.cpus.partition
>>>>> echo 0-3 > cpuset.cpus // 3 is nproc
>>>> What do you mean by "3 is nproc"? Are there only 3 CPUs in the 
>>>> system? What are the value of /sys/fs/cgroup/cpuset.cpu*?
>>> Yes, I tested it with qemu, only 3 cpus are available.
>>> # cat /sys/fs/cgroup/cpuset.cpus.effective
>>> 0-3
>>> This case is taking all cpus away from root, test should fail to be 
>>> a valid root, it should not rebuild scheduling domains.
>> I see. So there are 4 CPUs in the systems. So nproc should be 4. That 
>> is why I got confused when you said nproc is 3. I think you should 
>> clarify this in your patch.
>
> Sorry about that. Is it clear as below?
>
> It can be reproduced with cammands:
> cd /sys/fs/cgroup/
> mkdir test
> cd test/
> echo +cpuset > ../cgroup.subtree_control
> echo root > cpuset.cpus.partition
> # cat /sys/fs/cgroup/cpuset.cpus.effective
> 0-3
> echo 0-3 > cpuset.cpus // taking away all cpus from root

Yes, that looks good to me.

Thanks,
Longman