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([2601:600:947f:f020:85dc:d2b2:c5ee:e3c4]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8997c691113sm117137576d6.1.2026.02.24.06.30.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Feb 2026 06:30:32 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Tue, 24 Feb 2026 09:30:30 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [cgroups?] general protection fault in rebuild_sched_domains_locked To: Chen Ridong , Waiman Long , syzbot , cgroups@vger.kernel.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, mkoutny@suse.com, syzkaller-bugs@googlegroups.com, tj@kernel.org References: <6992351f.050a0220.2757fb.0035.GAE@google.com> <544a0eb5-3c03-463b-911b-6f3b8037f8e1@redhat.com> <30efbec6-b80d-471f-a445-5b7f06dd0f49@huaweicloud.com> <02712184-b1b7-4501-9e6e-b8d4432fb11f@redhat.com> <09d89416-2160-486e-8675-ffe898ac2612@huaweicloud.com> Content-Language: en-US In-Reply-To: <09d89416-2160-486e-8675-ffe898ac2612@huaweicloud.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2/24/26 1:56 AM, Chen Ridong wrote: > > On 2026/2/24 13:37, Waiman Long wrote: >> On 2/23/26 11:03 PM, Chen Ridong wrote: >>> On 2026/2/16 13:57, Waiman Long wrote: >>>> On 2/15/26 4:05 PM, syzbot wrote: >>>>> Hello, >>>>> >>>>> syzbot found the following issue on: >>>>> >>>>> HEAD commit:    37a93dd5c49b Merge tag 'net-next-7.0' of git://git.kernel... >>>>> git tree:       upstream >>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1649d073980000 >>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=a512b4a06724b76a >>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=460792609a79c085f79f >>>>> compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for >>>>> Debian) 2.44 >>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=152086e6580000 >>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=139c2eef980000 >>>>> >>>>> Downloadable assets: >>>>> disk image: >>>>> https://storage.googleapis.com/syzbot-assets/0dedaafff2ad/disk-37a93dd5.raw.xz >>>>> vmlinux: >>>>> https://storage.googleapis.com/syzbot-assets/aa7fae081497/vmlinux-37a93dd5.xz >>>>> kernel image: >>>>> https://storage.googleapis.com/syzbot-assets/9096b39b53e1/bzImage-37a93dd5.xz >>>>> >>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit: >>>>> Reported-by: syzbot+460792609a79c085f79f@syzkaller.appspotmail.com >>>>> >>>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 >>>>> R13: 00007fe00de15fac R14: 00007fe00de15fa0 R15: 00007fe00de15fa0 >>>>>    >>>>> Oops: general protection fault, probably for non-canonical address >>>>> 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI >>>>> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] >>>>> CPU: 1 UID: 0 PID: 5994 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) >>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google >>>>> 01/24/2026 >>>>> RIP: 0010:bitmap_subset include/linux/bitmap.h:433 [inline] >>>>> RIP: 0010:cpumask_subset include/linux/cpumask.h:836 [inline] >>>>> RIP: 0010:rebuild_sched_domains_locked+0x2aa/0x980 kernel/cgroup/cpuset.c:967 >>>>> Code: 7d 05 00 41 83 c4 01 89 de 48 83 c5 08 44 89 e7 e8 fb 76 05 00 41 39 dc >>>>> 0f 8d 4c 04 00 00 e8 fd 7c 05 00 48 89 e8 48 c1 e8 03 <42> 80 3c 30 00 0f 85 >>>>> 1d 06 00 00 48 8b 04 24 48 23 45 00 31 ff 44 >>>>> RSP: 0018:ffffc90003ecfbc0 EFLAGS: 00010246 >>>>> RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000020 >>>>> RDX: ffff888028de0000 RSI: ffffffff8200f003 RDI: ffffffff8df14f28 >>>>> RBP: 0000000000000000 R08: 0000000000000cc0 R09: 00000000ffffffff >>>>> R10: ffffffff8e7d95b3 R11: 0000000000000001 R12: 0000000000000000 >>>>> R13: 00000000000f4240 R14: dffffc0000000000 R15: 0000000000000000 >>>>> FS:  000055555c694500(0000) GS:ffff8881246a5000(0000) knlGS:0000000000000000 >>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>>> CR2: 0000001b2f463fff CR3: 000000003704c000 CR4: 00000000003526f0 >>>>> Call Trace: >>>>>    >>>>>    rebuild_sched_domains_cpuslocked kernel/cgroup/cpuset.c:983 [inline] >>>>>    rebuild_sched_domains+0x21/0x40 kernel/cgroup/cpuset.c:990 >>>>>    sched_rt_handler+0xb5/0xe0 kernel/sched/rt.c:2911 >>>>>    proc_sys_call_handler+0x47f/0x5a0 fs/proc/proc_sysctl.c:600 >>>>>    new_sync_write fs/read_write.c:595 [inline] >>>>>    vfs_write+0x6ac/0x1070 fs/read_write.c:688 >>>>>    ksys_write+0x12a/0x250 fs/read_write.c:740 >>>>>    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] >>>>>    do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94 >>>>>    entry_SYSCALL_64_after_hwframe+0x77/0x7f >>>>> RIP: 0033:0x7fe00db9bf79 >>>>> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 >>>>> 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 >>>>> 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 >>>>> RSP: 002b:00007fff27bcda88 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 >>>>> RAX: ffffffffffffffda RBX: 00007fe00de15fa0 RCX: 00007fe00db9bf79 >>>>> RDX: 00000000000000f6 RSI: 0000200000000000 RDI: 0000000000000003 >>>>> RBP: 00007fff27bcdaf0 R08: 0000000000000000 R09: 0000000000000000 >>>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 >>>>> R13: 00007fe00de15fac R14: 00007fe00de15fa0 R15: 00007fe00de15fa0 >>>>>    >>>>> Modules linked in: >>>>> ---[ end trace 0000000000000000 ]--- >>>>> RIP: 0010:bitmap_subset include/linux/bitmap.h:433 [inline] >>>>> RIP: 0010:cpumask_subset include/linux/cpumask.h:836 [inline] >>>>> RIP: 0010:rebuild_sched_domains_locked+0x2aa/0x980 kernel/cgroup/cpuset.c:967 >>>>> Code: 7d 05 00 41 83 c4 01 89 de 48 83 c5 08 44 89 e7 e8 fb 76 05 00 41 39 dc >>>>> 0f 8d 4c 04 00 00 e8 fd 7c 05 00 48 89 e8 48 c1 e8 03 <42> 80 3c 30 00 0f 85 >>>>> 1d 06 00 00 48 8b 04 24 48 23 45 00 31 ff 44 >>>>> RSP: 0018:ffffc90003ecfbc0 EFLAGS: 00010246 >>>>> RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000020 >>>>> RDX: ffff888028de0000 RSI: ffffffff8200f003 RDI: ffffffff8df14f28 >>>>> RBP: 0000000000000000 R08: 0000000000000cc0 R09: 00000000ffffffff >>>>> R10: ffffffff8e7d95b3 R11: 0000000000000001 R12: 0000000000000000 >>>>> R13: 00000000000f4240 R14: dffffc0000000000 R15: 0000000000000000 >>>>> FS:  000055555c694500(0000) GS:ffff8881246a5000(0000) knlGS:0000000000000000 >>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>>> CR2: 0000001b2f463fff CR3: 000000003704c000 CR4: 00000000003526f0 >>>>> ---------------- >>>>> Code disassembly (best guess), 1 bytes skipped: >>>>>      0:    05 00 41 83 c4           add    $0xc4834100,%eax >>>>>      5:    01 89 de 48 83 c5        add    %ecx,-0x3a7cb722(%rcx) >>>>>      b:    08 44 89 e7              or     %al,-0x19(%rcx,%rcx,4) >>>>>      f:    e8 fb 76 05 00           call   0x5770f >>>>>     14:    41 39 dc                 cmp    %ebx,%r12d >>>>>     17:    0f 8d 4c 04 00 00        jge    0x469 >>>>>     1d:    e8 fd 7c 05 00           call   0x57d1f >>>>>     22:    48 89 e8                 mov    %rbp,%rax >>>>>     25:    48 c1 e8 03              shr    $0x3,%rax >>>>> * 29:    42 80 3c 30 00           cmpb   $0x0,(%rax,%r14,1) <-- trapping >>>>> instruction >>>>>     2e:    0f 85 1d 06 00 00        jne    0x651 >>>>>     34:    48 8b 04 24              mov    (%rsp),%rax >>>>>     38:    48 23 45 00              and    0x0(%rbp),%rax >>>>>     3c:    31 ff                    xor    %edi,%edi >>>>>     3e:    44                       rex.R >>>> The cpuset.c:967 is: >>>> >>>>      966         for (i = 0; i < ndoms; ++i) { >>>>      967                 if (WARN_ON_ONCE(!cpumask_subset(doms[i], >>>> cpu_active_mask))) >>>>      968                         return; >>>> >>>> The oops was caused by accessing doms[i] which was kmalloc'ed in >>>> generate_sched_domains() by calling alloc_sched_domains() in >>>> kernel/sched/topology.c. Looking at the console log just before the oops, I saw >>>> >>>> [  124.398850][ T5994] FAULT_INJECTION: forcing a failure. >>>> [  124.398850][ T5994] name failslab, interval 1, probability 0, space 0, >>>> times 1 >>>> [  124.434865][ T5994] CPU: 1 UID: 0 PID: 5994 Comm: syz.0.17 Not tainted >>>> syzkaller #0 PREEMPT(full) >>>> [  124.434909][ T5994] Hardware name: Google Google Compute Engine/Google >>>> Compute Engine, BIOS Google 01/24/2026 >>>> [  124.434936][ T5994] Call Trace: >>>> [  124.434947][ T5994]  >>>> [  124.434959][ T5994]  dump_stack_lvl+0x100/0x190 >>>> [  124.435026][ T5994]  should_fail_ex.cold+0x5/0xa >>>> [  124.435062][ T5994]  ? rebuild_sched_domains_locked+0x51/0x980 >>>> [  124.435113][ T5994]  should_failslab+0xc2/0x120 >>>> [  124.435153][ T5994]  __kmalloc_noprof+0xe0/0x850 >>>> [  124.435195][ T5994]  rebuild_sched_domains_locked+0x51/0x980 >>>> [  124.435266][ T5994]  rebuild_sched_domains+0x21/0x40 >>>> [  124.435314][ T5994]  sched_rt_handler+0xb5/0xe0 >>>> [  124.435359][ T5994]  proc_sys_call_handler+0x47f/0x5a0 >>>> [  124.435413][ T5994]  ? __pfx_proc_sys_call_handler+0x10/0x10 >>>> [  124.435475][ T5994]  vfs_write+0x6ac/0x1070 >>>> [  124.435511][ T5994]  ? __pfx_proc_sys_write+0x10/0x10 >>>> [  124.435562][ T5994]  ? __pfx_vfs_write+0x10/0x10 >>>> [  124.435597][ T5994]  ? __pfx_do_sys_openat2+0x10/0x10 >>>> [  124.435664][ T5994]  ksys_write+0x12a/0x250 >>>> [  124.435696][ T5994]  ? __pfx_ksys_write+0x10/0x10 >>>> [  124.435730][ T5994]  ? do_user_addr_fault+0x8d6/0x12f0 >>>> [  124.435787][ T5994]  do_syscall_64+0x106/0xf80 >>>> [  124.435834][ T5994]  ? clear_bhb_loop+0x40/0x90 >>>> [  124.435875][ T5994]  entry_SYSCALL_64_after_hwframe+0x77/0x7f >>>> >>>> So it looks like the oops may be expected. It may not be a bug in the cpuset >>>> AFAICS. >>>> >>> Hi Longman, >>> >>> Thank you for looking into this issue. >>> >>> Since partition_sched_domains_locked can handle the situation where 'doms' is >>> NULL, I think we should make it robust and fix it. >>> >>> The fix can be implemented as follows: >>> >>> In cpuset.c at line 964: >>> >>>          for (i = 0; i < ndoms; ++i) { >>> -               if (WARN_ON_ONCE(!cpumask_subset(doms[i], cpu_active_mask))) >>> +               if (doms && WARN_ON_ONCE(!cpumask_subset(doms[i], >>> +                                         cpu_active_mask))) >>>                          return; >>>          } >>> >> The problem is that doms is not NULL. It is 0xdffffc0000000000 as shown in the >> dmesg log. So the null check here won't do any good in this particular case. In >> fact, there is already a null check right after alloc_sched_domains() above. >> > Looking at the dmesg log: > > [ 124.660383][ T5994] Oops: general protection fault, probably for > non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI > [ 124.672366][ T5994] KASAN: null-ptr-deref in range > [0x0000000000000000-0x0000000000000007] > > The address 0xdffffc0000000000 appears to be the KASAN shadow offset, which is > configured in: > > arch/x86/Kconfig:413 > config KASAN_SHADOW_OFFSET > hex > depends on KASAN > default 0xdffffc0000000000 > > This indicates that doms is actually NULL. In generate_sched_domains(), doms is > first assigned to NULL. > > Indeed, there is already a NULL check right after alloc_sched_domains(), when > doms is NULL, it returns ndoms = 1 and doms = NULL. Therefore, I believe we need > to add 'doms' check in the rebuild_sched_domains_locked. > Right. The for loop shouldn't be run if doms is NULL. Sure. Please send a patch to make this change. Cheers, Longman