Re: [PATCH] cgroup/cpuset: fix panic caused by partcmd_update

[Waiman Long <longman@redhat.com>]

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*?
>
> 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@huawei.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.

Cheers,
Longman