syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5786/1:b..l
rcu: 	(detected by 1, t=10502 jiffies, g=20893, q=251 ncpus=2)
task:syz-executor    state:R  running task     stack:21352 pid:5786  ppid:5783   flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 preempt_schedule_irq+0xb5/0x140 kernel/sched/core.c:7010
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:preempt_count arch/x86/include/asm/preempt.h:27 [inline]
RIP: 0010:rcu_lockdep_current_cpu_online+0x0/0x120 kernel/rcu/tree.c:4222
Code: df e8 f4 ed 6c 00 4c 85 3b 0f 95 c0 5b 41 5e 41 5f c3 89 fe 89 fb 48 c7 c7 40 50 d3 8c e8 b8 26 e1 02 89 df e9 53 ff ff ff 90 <f3> 0f 1e fa 41 57 41 56 53 65 8b 0d 48 cc 93 7e b0 01 f7 c1 00 00
RSP: 0018:ffffc9000462fa48 EFLAGS: 00000202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: f1c5425336e07d00
RDX: 0000000000000000 RSI: ffffffff8afc66e0 RDI: ffffffff8afc66a0
RBP: 0000000000000001 R08: dffffc0000000000 R09: 1ffffffff21b46a4
R10: dffffc0000000000 R11: fffffbfff21b46a5 R12: dffffc0000000000
R13: 00000000000001e0 R14: 000000000007d4c0 R15: ffff888019640000
 rcu_read_lock_held_common kernel/rcu/update.c:112 [inline]
 rcu_read_lock_held+0x1e/0x40 kernel/rcu/update.c:348
 lookup_page_ext mm/page_ext.c:240 [inline]
 page_ext_get+0x193/0x2b0 mm/page_ext.c:509
 __reset_page_owner+0x2e/0x190 mm/page_owner.c:145
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1154 [inline]
 free_unref_page_prepare+0x7ce/0x8e0 mm/page_alloc.c:2336
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2429
 discard_slab mm/slub.c:2122 [inline]
 __unfreeze_partials+0x1cf/0x210 mm/slub.c:2662
 put_cpu_partial+0x17c/0x250 mm/slub.c:2738
 __slab_free+0x31d/0x410 mm/slub.c:3686
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xe0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:305
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4d0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3485 [inline]
 slab_alloc mm/slub.c:3493 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3500 [inline]
 kmem_cache_alloc+0x11e/0x2e0 mm/slub.c:3509
 getname_flags+0xbb/0x500 fs/namei.c:140
 user_path_at_empty+0x2c/0x60 fs/namei.c:2908
 user_path_at include/linux/namei.h:57 [inline]
 ksys_umount fs/namespace.c:1912 [inline]
 __do_sys_umount fs/namespace.c:1920 [inline]
 __se_sys_umount fs/namespace.c:1918 [inline]
 __x64_sys_umount+0xf5/0x170 fs/namespace.c:1918
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f7cfd58fe97
RSP: 002b:00007fff69f3dba8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 00007f7cfd611bdd RCX: 00007f7cfd58fe97
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007fff69f3ecf0
RBP: 00007fff69f3ecdc R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff69f3ecf0
R13: 00007f7cfd611bdd R14: 0000000000031639 R15: 00007fff69f3ed30
 </TASK>
rcu: rcu_preempt kthread starved for 10025 jiffies! g20893 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:26920 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_timeout+0x160/0x280 kernel/time/timer.c:2167
 rcu_gp_fqs_loop+0x302/0x1560 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x99/0x380 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.6.100-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:148
Code: cc cc cc cc cc cc cc f3 0f 1e fa 0f 0b 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 66 90 0f 00 2d e3 16 3b 00 f3 0f 1e fa fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc 66 0f 1f 00 55 41 57 41 56
RSP: 0018:ffffffff8ca07d80 EFLAGS: 000002c6
RAX: d9d9f22fe0ed2c00 RBX: ffffffff81619a5b RCX: d9d9f22fe0ed2c00
RDX: 0000000000000001 RSI: ffffffff8aaaba40 RDI: ffffffff8afc6700
RBP: ffffffff8ca07eb8 R08: ffff8880b8e36d4b R09: 1ffff110171c6da9
R10: dffffc0000000000 R11: ffffed10171c6daa R12: ffffffff8e4a7da8
R13: 0000000000000000 R14: 0000000000000000 R15: 1ffffffff1952670
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe136ccf1b1 CR3: 000000005ba7e000 CR4: 00000000003506f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:108 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:753
 default_idle_call+0x6c/0xa0 kernel/sched/idle.c:97
 cpuidle_idle_call kernel/sched/idle.c:170 [inline]
 do_idle+0x1eb/0x510 kernel/sched/idle.c:282
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:380
 rest_init+0x2e2/0x300 init/main.c:732
 arch_call_rest_init+0xe/0x10 init/main.c:829
 start_kernel+0x459/0x4e0 init/main.c:1074
 x86_64_start_reservations+0x2a/0x30 arch/x86/kernel/head64.c:555
 x86_64_start_kernel+0x60/0x60 arch/x86/kernel/head64.c:536
 secondary_startup_64_no_verify+0x179/0x17b
 </TASK>