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Message-ID: <68b70218.050a0220.3db4df.01d1.GAE@google.com> Date: Tue, 02 Sep 2025 07:41:28 -0700 From: syzbot <syzbot+5b4f4f81240931b16844@...kaller.appspotmail.com> To: axboe@...nel.dk, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, syzkaller-bugs@...glegroups.com Subject: Re: [syzbot] [block?] [mm?] INFO: rcu detected stall in wb_workfn (4) syzbot has found a reproducer for the following issue on: HEAD commit: b320789d6883 Linux 6.17-rc4 git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=1406ae62580000 kernel config: https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a dashboard link: https://syzkaller.appspot.com/bug?extid=5b4f4f81240931b16844 compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133b5e34580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1639ca42580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/daf1f6c847dd/disk-b320789d.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/fbeb0bd5d987/vmlinux-b320789d.xz kernel image: https://storage.googleapis.com/syzbot-assets/a85084f8e16b/bzImage-b320789d.xz IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+5b4f4f81240931b16844@...kaller.appspotmail.com rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P1288/1:b.el P5851/1:b..l rcu: (detected by 0, t=11117 jiffies, g=9285, q=859 ncpus=2) task:udevd state:R running task stack:27176 pid:5851 tgid:5851 ppid:5218 task_flags:0x400140 flags:0x00004002 Call Trace: <TASK> context_switch kernel/sched/core.c:5357 [inline] __schedule+0x1190/0x5de0 kernel/sched/core.c:6961 preempt_schedule_common+0x44/0xc0 kernel/sched/core.c:7145 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12 __raw_spin_unlock include/linux/spinlock_api_smp.h:143 [inline] _raw_spin_unlock+0x3e/0x50 kernel/locking/spinlock.c:186 spin_unlock include/linux/spinlock.h:391 [inline] wp_page_copy mm/memory.c:3653 [inline] do_wp_page+0x177b/0x4f00 mm/memory.c:4013 handle_pte_fault mm/memory.c:6068 [inline] __handle_mm_fault+0x1b2d/0x2a50 mm/memory.c:6195 handle_mm_fault+0x589/0xd10 mm/memory.c:6364 do_user_addr_fault+0x60c/0x1370 arch/x86/mm/fault.c:1336 handle_page_fault arch/x86/mm/fault.c:1476 [inline] exc_page_fault+0x5c/0xb0 arch/x86/mm/fault.c:1532 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623 RIP: 0033:0x7f5c948b5db7 RSP: 002b:00007ffd6b822260 EFLAGS: 00010202 RAX: 0000000000006010 RBX: 00000000000001f0 RCX: 000055b18d0b4fe0 RDX: 0000000000006010 RSI: 000055b18d0aefd0 RDI: 00007f5c949f1ac0 RBP: 00007f5c949f1ac0 R08: 00000000000001f0 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 000055b18d0aefd0 R13: 00007f5c949f1ac0 R14: 00000000000001f0 R15: 00007f5c949f1ac0 </TASK> task:kworker/u8:5 state:R running task stack:22344 pid:1288 tgid:1288 ppid:2 task_flags:0x24248060 flags:0x00004000 Workqueue: writeback wb_workfn (flush-8:0) Call Trace: <TASK> context_switch kernel/sched/core.c:5357 [inline] __schedule+0x1190/0x5de0 kernel/sched/core.c:6961 preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:7288 irqentry_exit+0x36/0x90 kernel/entry/common.c:197 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702 RIP: 0010:__sanitizer_cov_trace_switch+0x7f/0x90 kernel/kcov.c:336 Code: 39 de 75 e2 5b 5d 41 5c 41 5d 41 5e c3 cc cc cc cc 41 bd 07 00 00 00 48 83 f8 40 74 be 5b 5d 41 5c 41 5d 41 5e e9 91 66 db 09 <41> bd 01 00 00 00 eb a9 41 bd 05 00 00 00 eb a1 90 90 90 90 90 90 RSP: 0018:ffffc90004d1e918 EFLAGS: 00000246 RAX: 0000000000000008 RBX: ffff888029fc9a50 RCX: ffffffff863bcae4 RDX: ffff888028ca2440 RSI: ffffffff8c136f20 RDI: 0000000000000000 RBP: ffffffff8c136f20 R08: 0000000000000005 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: ffff888029fc9a48 R14: ffff888027e99000 R15: ffffc90004d1eb60 blk_mq_dispatch_rq_list+0x428/0x1e20 block/blk-mq.c:2121 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline] blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline] __blk_mq_sched_dispatch_requests+0xcb7/0x15f0 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329 blk_mq_run_hw_queue+0x349/0x670 block/blk-mq.c:2358 blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2919 blk_mq_flush_plug_list block/blk-mq.c:2967 [inline] blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2939 blk_add_rq_to_plug+0x1ca/0x540 block/blk-mq.c:1390 blk_mq_submit_bio+0x1a6b/0x2a10 block/blk-mq.c:3212 __submit_bio+0x3cf/0x690 block/blk-core.c:635 __submit_bio_noacct_mq block/blk-core.c:722 [inline] submit_bio_noacct_nocheck+0x660/0xd30 block/blk-core.c:751 submit_bio_noacct+0xc20/0x1ed0 block/blk-core.c:874 ext4_io_submit+0xa6/0x140 fs/ext4/page-io.c:404 ext4_do_writepages+0xe42/0x3cf0 fs/ext4/inode.c:2951 ext4_writepages+0x37a/0x7d0 fs/ext4/inode.c:3025 do_writepages+0x27a/0x600 mm/page-writeback.c:2634 __writeback_single_inode+0x160/0xfb0 fs/fs-writeback.c:1680 writeback_sb_inodes+0x60d/0xfa0 fs/fs-writeback.c:1976 __writeback_inodes_wb+0xf8/0x2d0 fs/fs-writeback.c:2047 wb_writeback+0x7f3/0xb70 fs/fs-writeback.c:2158 wb_check_old_data_flush fs/fs-writeback.c:2262 [inline] wb_do_writeback fs/fs-writeback.c:2315 [inline] wb_workfn+0x8ca/0xbe0 fs/fs-writeback.c:2343 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236 process_scheduled_works kernel/workqueue.c:3319 [inline] worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400 kthread+0x3c5/0x780 kernel/kthread.c:463 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> rcu: rcu_preempt kthread starved for 11117 jiffies! g9285 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:27928 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00004000 Call Trace: <TASK> context_switch kernel/sched/core.c:5357 [inline] __schedule+0x1190/0x5de0 kernel/sched/core.c:6961 __schedule_loop kernel/sched/core.c:7043 [inline] schedule+0xe7/0x3a0 kernel/sched/core.c:7058 schedule_timeout+0x123/0x290 kernel/time/sleep_timeout.c:99 rcu_gp_fqs_loop+0x1ea/0xb00 kernel/rcu/tree.c:2083 rcu_gp_kthread+0x270/0x380 kernel/rcu/tree.c:2285 kthread+0x3c5/0x780 kernel/kthread.c:463 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> rcu: Stack dump where RCU GP kthread last ran: CPU: 0 UID: 0 PID: 5513 Comm: dhcpcd Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x8/0x20 kernel/kcov.c:314 Code: bf 03 00 00 00 e9 58 fe ff ff 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 8b 0c 24 <89> f2 89 fe bf 05 00 00 00 e9 2a fe ff ff 66 2e 0f 1f 84 00 00 00 RSP: 0018:ffffc90003277730 EFLAGS: 00000202 RAX: 0000000000000001 RBX: ffff8880b853fe80 RCX: ffffffff81af8ea1 RDX: ffff8880213e4880 RSI: 0000000000000001 RDI: 0000000000000000 RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: dffffc0000000000 R13: ffffed10170a7fd1 R14: 0000000000000001 R15: 0000000000000001 FS: 00007fd829003740(0000) GS:ffff8881246b8000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f9856c3ffdc CR3: 00000000782b2000 CR4: 00000000003526f0 Call Trace: <TASK> csd_lock_wait kernel/smp.c:342 [inline] smp_call_function_many_cond+0xe21/0x1600 kernel/smp.c:877 on_each_cpu_cond_mask+0x40/0x90 kernel/smp.c:1044 __flush_tlb_multi arch/x86/include/asm/paravirt.h:91 [inline] flush_tlb_multi arch/x86/mm/tlb.c:1361 [inline] flush_tlb_mm_range+0x4a0/0x17a0 arch/x86/mm/tlb.c:1451 dup_mmap+0xfa2/0x21d0 mm/mmap.c:1873 dup_mm kernel/fork.c:1485 [inline] copy_mm kernel/fork.c:1537 [inline] copy_process+0x4081/0x7690 kernel/fork.c:2175 kernel_clone+0xfc/0x930 kernel/fork.c:2605 __do_sys_clone+0xce/0x120 kernel/fork.c:2748 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fd8290d7636 Code: 89 df e8 6d e8 f6 ff 45 31 c0 31 d2 31 f6 64 48 8b 04 25 10 00 00 00 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 52 89 c5 85 c0 75 31 64 48 8b 04 25 10 00 00 RSP: 002b:00007ffc8dce2200 EFLAGS: 00000246 ORIG_RAX: 0000000000000038 RAX: ffffffffffffffda RBX: 00007ffc8dce2208 RCX: 00007fd8290d7636 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011 RBP: 00007ffc8dd02750 R08: 0000000000000000 R09: 0000000000000001 R10: 00007fd829003a10 R11: 0000000000000246 R12: 00007ffc8dce2340 R13: 0000000000000000 R14: 0000000000000000 R15: 0000560acbd41ac0 </TASK> --- If you want syzbot to run the reproducer, reply with: #syz test: git://repo/address.git branch-or-commit-hash If you attach or paste a git patch, syzbot will apply it before testing.
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