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

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Message-ID: <a3ff05d8-3acd-4d7d-b2b5-3c512fe93cbf@huawei.com>
Date: Tue, 30 Jul 2024 11:46:35 +0800
From: chenridong <chenridong@...wei.com>
To: Waiman Long <longman@...hat.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 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

Thanks
Ridong
>>
>>>>
>>>> This issue is caused by the incorrect rebuilding of scheduling domains.
>>>> In this scenario, test/cpuset.cpus.partition should be an invalid root
>>>> and should not trigger the rebuilding of scheduling domains. When 
>>>> calling
>>>> update_parent_effective_cpumask with partcmd_update, if newmask is not
>>>> null, it should recheck newmask whether there are cpus is available
>>>> for parect/cs that has tasks.
>>>>
>>>> Fixes: 0c7f293efc87 ("cgroup/cpuset: Add 
>>>> cpuset.cpus.exclusive.effective for v2")
>>>> Signed-off-by: Chen Ridong <chenridong@...wei.com>
>>>> ---
>>>>   kernel/cgroup/cpuset.c | 2 ++
>>>>   1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>>>> index 40ec4abaf440..a9b6d56eeffa 100644
>>>> --- a/kernel/cgroup/cpuset.c
>>>> +++ b/kernel/cgroup/cpuset.c
>>>> @@ -1991,6 +1991,8 @@ static int 
>>>> update_parent_effective_cpumask(struct cpuset *cs, int cmd,
>>>>               part_error = PERR_CPUSEMPTY;
>>>>               goto write_error;
>>>>           }
>>>> +        /* Check newmask again, whether cpus are available for 
>>>> parent/cs */
>>>> +        nocpu |= tasks_nocpu_error(parent, cs, newmask);
>>>>           /*
>>>>            * partcmd_update with newmask:
>>>
>>> The code change looks reasonable to me. However, I would like to know 
>>> more about the reproduction steps.
> 
> I am OK with this patch other than missing some information in your 
> reproduction step.
> 
> Cheers,
> Longman
> 
>