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

[Waiman Long]

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.
> > > 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@xxxxxxxxxx>
> > > ---
> > >   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