INFO: rcu detected stall in mas_preallocate

Status: upstream: reported syz repro on 2025/12/30 16:49
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+273120320ac27f720690@syzkaller.appspotmail.com
First crash: 209d, last: 209d
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/01/01 linux-6.6.y (ToT) 5fa4793a2d2d syz [report] INFO: rcu detected stall in corrupted
2026/01/01 upstream (ToT) b69053dd3ffb syz Didn't crash
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in mas_preallocate (2) mm 1 syz done error 11 44d 595d 0/29 upstream: reported syz repro on 2024/12/09 09:12
android-6-12 INFO: rcu detected stall in mas_preallocate 1 2 354d 369d 0/1 auto-obsoleted due to no activity on 2025/11/05 15:42
linux-6.1 INFO: rcu detected stall in mas_preallocate 1 1 319d 319d 0/3 auto-obsoleted due to no activity on 2025/12/20 06:13
▶ ▼ Fix bisection attempts (3)
Created Duration User Patch Repo Result
2026/03/26 14:55 1m fix candidate upstream error job log
2026/02/24 01:07 1m fix candidate upstream error job log
2026/01/24 01:56 1m fix candidate upstream error job log

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P48/1:b..l P5978/1:b..l
rcu: 	(detected by 1, t=10502 jiffies, g=11365, q=598 ncpus=2)
task:sed             state:R  running task     stack:24232 pid:5978  ppid:5977   flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 preempt_schedule_irq+0xb5/0x140 kernel/sched/core.c:7009
 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:check_kcov_mode kernel/kcov.c:182 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:245 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp8+0x10/0x80 kernel/kcov.c:320
Code: 11 10 48 89 74 11 18 48 89 44 11 20 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 48 8b 04 24 65 48 8b 0d b0 20 7e 7e <65> 8b 15 b1 20 7e 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75
RSP: 0018:ffffc900036f7490 EFLAGS: 00000246
RAX: ffffffff81e7d2f1 RBX: 0000000000000000 RCX: ffff88802dfcbc00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: dffffc0000000000 R09: 1ffffffff21b28a0
R10: dffffc0000000000 R11: fffffbfff21b28a1 R12: 0000000000000000
R13: 1ffffffff2de0b30 R14: ffff8880191072e0 R15: 0000000000000001
 __page_table_check_zero+0x191/0x4b0 mm/page_table_check.c:153
 prep_new_page mm/page_alloc.c:1561 [inline]
 get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
 __alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
 alloc_slab_page+0x5d/0x170 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2e0 mm/slub.c:2081
 ___slab_alloc+0xc6d/0x1300 mm/slub.c:3253
 __kmem_cache_alloc_bulk mm/slub.c:3995 [inline]
 kmem_cache_alloc_bulk+0x1e6/0x5b0 mm/slub.c:4070
 mt_alloc_bulk lib/maple_tree.c:167 [inline]
 mas_alloc_nodes+0x471/0x8c0 lib/maple_tree.c:1289
 mas_node_count_gfp lib/maple_tree.c:1347 [inline]
 mas_preallocate+0xa44/0x1190 lib/maple_tree.c:5535
 vma_iter_prealloc mm/internal.h:1152 [inline]
 __mmap_region mm/mmap.c:2783 [inline]
 mmap_region+0xdbf/0x2020 mm/mmap.c:2941
 do_mmap+0x92f/0x10a0 mm/mmap.c:1385
 vm_mmap_pgoff+0x1c0/0x400 mm/util.c:556
 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: 0033:0x7fafb350c242
RSP: 002b:00007ffd7e379358 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fafb350c242
RDX: 0000000000000003 RSI: 0000000000002000 RDI: 0000000000000000
RBP: 0000000000000022 R08: 00000000ffffffff R09: 0000000000000000
R10: 0000000000000022 R11: 0000000000000246 R12: 0000000000002000
R13: 0000000000000001 R14: 000000351f6bcf60 R15: 0000000000000000
 </TASK>
task:kworker/u4:3    state:R  running task     stack:24264 pid:48    ppid:2      flags:0x00004000
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 preempt_schedule_irq+0xb5/0x140 kernel/sched/core.c:7009
 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:instrument_atomic_read include/linux/instrumented.h:68 [inline]
RIP: 0010:atomic_read include/linux/atomic/atomic-instrumented.h:32 [inline]
RIP: 0010:folio_memcg_lock+0x18f/0x2f0 mm/memcontrol.c:2165
Code: 48 c7 44 24 60 00 00 00 00 9c 8f 44 24 60 f6 44 24 61 02 0f 85 85 00 00 00 41 f7 c5 00 02 00 00 74 01 fb 4d 8d a7 40 09 00 00 <4c> 89 e7 be 04 00 00 00 e8 74 f6 f8 ff 4c 89 e0 48 c1 e8 03 48 b9
RSP: 0018:ffffc90000b96ae0 EFLAGS: 00000206
RAX: 9698d53b80b29100 RBX: ffffea0001d9fc80 RCX: 9698d53b80b29100
RDX: dffffc0000000000 RSI: ffffffff8aaabce0 RDI: ffffffff8afc6f80
RBP: ffffc90000b96bb0 R08: ffffffff90d945a7 R09: 1ffffffff21b28b4
R10: dffffc0000000000 R11: fffffbfff21b28b5 R12: ffff88814125a940
R13: 0000000000000286 R14: ffffffff81e408e9 R15: ffff88814125a000
 __folio_start_writeback+0x15d/0xf80 mm/page-writeback.c:3017
 ext4_bio_write_folio+0xedc/0x2250 fs/ext4/page-io.c:566
 mpage_submit_folio+0x237/0x3c0 fs/ext4/inode.c:1908
 mpage_map_and_submit_buffers fs/ext4/inode.c:2154 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2293 [inline]
 ext4_do_writepages+0x1d01/0x38d0 fs/ext4/inode.c:2718
 ext4_writepages+0x1a8/0x2f0 fs/ext4/inode.c:2807
 do_writepages+0x3a2/0x600 mm/page-writeback.c:2575
 __writeback_single_inode+0x153/0xee0 fs/fs-writeback.c:1635
 writeback_sb_inodes+0x77c/0xef0 fs/fs-writeback.c:1926
 __writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:1997
 wb_writeback+0x464/0xba0 fs/fs-writeback.c:2107
 wb_check_old_data_flush fs/fs-writeback.c:2211 [inline]
 wb_do_writeback fs/fs-writeback.c:2264 [inline]
 wb_workfn+0xabc/0xe20 fs/fs-writeback.c:2292
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 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: rcu_preempt kthread starved for 10587 jiffies! g11365 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:26568 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 schedule+0xbd/0x170 kernel/sched/core.c:6773
 schedule_timeout+0x160/0x280 kernel/time/timer.c:2168
 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: 5979 Comm: syz.3.20 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:arch_static_branch arch/x86/include/asm/jump_label.h:27 [inline]
RIP: 0010:static_key_false include/linux/jump_label.h:207 [inline]
RIP: 0010:native_write_msr arch/x86/include/asm/msr.h:147 [inline]
RIP: 0010:wrmsr arch/x86/include/asm/msr.h:254 [inline]
RIP: 0010:native_apic_msr_write+0x39/0x50 arch/x86/include/asm/apic.h:196
Code: 74 2a 83 ff 30 74 25 eb 10 81 ff d0 00 00 00 74 1b 81 ff e0 00 00 00 74 13 c1 ef 04 81 c7 00 08 00 00 89 f9 89 f0 31 d2 0f 30 <66> 90 c3 f3 0f 1e fa 89 f6 31 d2 e9 f7 36 19 03 0f 1f 80 00 00 00
RSP: 0018:ffffc90003707a70 EFLAGS: 00000046
RAX: 000000000000003e RBX: ffff8880b8e28280 RCX: 0000000000000838
RDX: 0000000000000000 RSI: 000000000000003e RDI: 0000000000000838
RBP: 000000000000003e R08: ffffffff8e4a212f R09: 1ffffffff1c94425
R10: dffffc0000000000 R11: fffffbfff1c94426 R12: ffff8880b8e282c0
R13: ffff8880b8e282b8 R14: 0000000000000020 R15: dffffc0000000000
FS:  000055557c1e8500(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b34363fff CR3: 0000000024198000 CR4: 00000000003506f0
Call Trace:
 <TASK>
 apic_write arch/x86/include/asm/apic.h:404 [inline]
 lapic_next_event+0x11/0x20 arch/x86/kernel/apic/apic.c:448
 clockevents_program_min_delta+0x1a9/0x340 kernel/time/clockevents.c:248
 hrtimer_start_range_ns+0xbfb/0x1000 kernel/time/hrtimer.c:1352
 posixtimer_rearm+0x135/0x340 kernel/time/posix-timers.c:268
 dequeue_signal+0x1ba/0x4b0 kernel/signal.c:706
 get_signal+0x551/0x1400 kernel/signal.c:2782
 arch_do_signal_or_restart+0x9c/0x7b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xf6/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
 do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:87
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f1764519000
Code: c7 44 24 20 c0 ff ff ff 48 c7 44 24 18 3f 00 00 00 48 c7 44 24 10 40 00 00 00 48 c7 44 24 08 00 00 00 00 e9 ad fd ff ff 66 90 <48> c7 c0 a8 ff ff ff 64 48 03 04 25 00 00 00 00 c3 66 2e 0f 1f 84
RSP: 002b:00007ffec9376918 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 00007f17647e5fa0 RCX: 00007f1764613f91
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f1764613f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f17647e5fa0 R14: 00007f17647e5fa0 R15: 0000000000000004
 </TASK>
sched: RT throttling activated

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/30 16:48 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in mas_preallocate
* Struck through repros no longer work on HEAD.