On 4/20/2020 2:47 PM, Dan Carpenter wrote: > 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); If a req have got into io_init_req(), than it'll be put at some point with io_put_req(). io_req_work_drop_env() called from there will clean up 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. The same should happen with req->fixed_file_refs, though I don't remember in details. > > 5898 io_consume_sqe(ctx); > 5899 /* will complete beyond this point, count as submitted */ > 5900 submitted++; Regarding, "--submitted" patch -- we take 1 ctx->refs per request, which is put in io_put_req(). So after a request passes the line above (5900), it's ref will be eventually dropped in io_put_req() and friends. And it's a bit more peculiar because io_submit_sqes() batch-takes N refs first, and then puts unused back at the end. > 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 > -- Pavel Begunkov
