On Sun, Apr 19, 2020 at 12:06:26PM +0800, Hillf Danton wrote: > > Sat, 18 Apr 2020 11:59:13 -0700 > > > > syzbot found the following crash on: > > > > HEAD commit: 8f3d9f35 Linux 5.7-rc1 > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=115720c3e00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=5d351a1019ed81a2 > > dashboard link: https://syzkaller.appspot.com/bug?extid=66243bb7126c410cefe6 > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > Unfortunately, I don't have any reproducer for this crash yet. > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+66243bb7126c410cefe6@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > rcu: INFO: rcu_preempt self-detected stall on CPU > > rcu: 0-....: (10500 ticks this GP) idle=57e/1/0x4000000000000002 softirq=44329/44329 fqs=5245 > > (t=10502 jiffies g=79401 q=2096) > > NMI backtrace for cpu 0 > > CPU: 0 PID: 23184 Comm: syz-executor.5 Not tainted 5.7.0-rc1-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > Call Trace: > > <IRQ> > > __dump_stack lib/dump_stack.c:77 [inline] > > dump_stack+0x188/0x20d lib/dump_stack.c:118 > > nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101 > > nmi_trigger_cpumask_backtrace+0x231/0x27e lib/nmi_backtrace.c:62 > > trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline] > > rcu_dump_cpu_stacks+0x19b/0x1e5 kernel/rcu/tree_stall.h:254 > > print_cpu_stall kernel/rcu/tree_stall.h:475 [inline] > > check_cpu_stall kernel/rcu/tree_stall.h:549 [inline] > > rcu_pending kernel/rcu/tree.c:3225 [inline] > > rcu_sched_clock_irq.cold+0x55d/0xcfa kernel/rcu/tree.c:2296 > > update_process_times+0x25/0x60 kernel/time/timer.c:1727 > > tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176 > > tick_sched_timer+0x4e/0x140 kernel/time/tick-sched.c:1320 > > __run_hrtimer kernel/time/hrtimer.c:1520 [inline] > > __hrtimer_run_queues+0x5ca/0xed0 kernel/time/hrtimer.c:1584 > > hrtimer_interrupt+0x312/0x770 kernel/time/hrtimer.c:1646 > > local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1113 [inline] > > smp_apic_timer_interrupt+0x15b/0x600 arch/x86/kernel/apic/apic.c:1138 > > apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829 > > </IRQ> > > RIP: 0010:io_ring_ctx_wait_and_kill+0x98/0x5a0 fs/io_uring.c:7301 > > Code: 01 00 00 4d 89 f4 48 b8 00 00 00 00 00 fc ff df 4c 89 ed 49 c1 ec 03 48 c1 ed 03 49 01 c4 48 01 c5 eb 1c e8 3a ea 9d ff f3 90 <41> 80 3c 24 00 0f 85 53 04 00 00 48 83 bb 10 01 00 00 00 74 21 e8 > > RSP: 0018:ffffc9000897fdf0 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13 > > RAX: ffff888024082080 RBX: ffff88808df8e000 RCX: 1ffff9200112ffab > > RDX: 0000000000000000 RSI: ffffffff81d549c6 RDI: ffff88808df8e300 > > RBP: ffffed1011bf1c2c R08: 0000000000000001 R09: ffffed1011bf1c61 > > R10: ffff88808df8e307 R11: ffffed1011bf1c60 R12: ffffed1011bf1c22 > > R13: ffff88808df8e160 R14: ffff88808df8e110 R15: ffffffff81d54ed0 > > io_uring_release+0x3e/0x50 fs/io_uring.c:7324 > > __fput+0x33e/0x880 fs/file_table.c:280 > > task_work_run+0xf4/0x1b0 kernel/task_work.c:123 > > tracehook_notify_resume include/linux/tracehook.h:188 [inline] > > exit_to_usermode_loop+0x2fa/0x360 arch/x86/entry/common.c:165 > > prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline] > > syscall_return_slowpath arch/x86/entry/common.c:279 [inline] > > do_syscall_64+0x6b1/0x7d0 arch/x86/entry/common.c:305 > > entry_SYSCALL_64_after_hwframe+0x49/0xb3 > > Make io ring ctx's percpu_ref balanced. > > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -5904,6 +5904,7 @@ static int io_submit_sqes(struct io_ring > fail_req: > io_cqring_add_event(req, err); > io_double_put_req(req); > + --submitted; > break; > } fs/io_uring.c 5880 for (i = 0; i < nr; i++) { 5881 const struct io_uring_sqe *sqe; 5882 struct io_kiocb *req; 5883 int err; 5884 5885 sqe = io_get_sqe(ctx); 5886 if (unlikely(!sqe)) { 5887 io_consume_sqe(ctx); 5888 break; 5889 } 5890 req = io_alloc_req(ctx, statep); 5891 if (unlikely(!req)) { 5892 if (!submitted) 5893 submitted = -EAGAIN; 5894 break; 5895 } 5896 5897 err = io_init_req(ctx, req, sqe, statep, async); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ On the success path io_init_req() takes some references like: get_cred(req->work.creds); That one is probably buggy and should be put if the call to: return io_req_set_file(state, req, fd, sqe_flags); fails... But io_req_set_file() takes some other references if it succeeds like percpu_ref_get(req->fixed_file_refs); and it's not clear that those are released if io_submit_sqe() fails. 5898 io_consume_sqe(ctx); 5899 /* will complete beyond this point, count as submitted */ 5900 submitted++; 5901 5902 if (unlikely(err)) { 5903 fail_req: 5904 io_cqring_add_event(req, err); 5905 io_double_put_req(req); 5906 break; 5907 } 5908 5909 trace_io_uring_submit_sqe(ctx, req->opcode, req->user_data, 5910 true, async); 5911 err = io_submit_sqe(req, sqe, statep, &link); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ here 5912 if (err) 5913 goto fail_req; 5914 } regards, dan carpenter
