On Fri, 6 Aug 2021 at 22:39, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote: > > syzbot <syzbot+d40a01556c761b2cb385@xxxxxxxxxxxxxxxxxxxxxxxxx> writes: > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 1d67c8d993ba Merge tag 'soc-fixes-5.14-1' of git://git.ker.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=11b40232300000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=f1b998c1afc13578 > > dashboard link: https://syzkaller.appspot.com/bug?extid=d40a01556c761b2cb385 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12453812300000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11225922300000 > > > > Bisection is inconclusive: the issue happens on the oldest tested release. > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=127cac6a300000 > > final oops: https://syzkaller.appspot.com/x/report.txt?x=117cac6a300000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=167cac6a300000 > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+d40a01556c761b2cb385@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > INFO: task syz-executor299:8807 blocked for more than 143 seconds. > > Not tainted 5.14.0-rc1-syzkaller #0 > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > task:syz-executor299 state:D stack:29400 pid: 8807 ppid: 8806 flags:0x00000000 > > Call Trace: > > context_switch kernel/sched/core.c:4683 [inline] > > __schedule+0x93a/0x26f0 kernel/sched/core.c:5940 > > schedule+0xd3/0x270 kernel/sched/core.c:6019 > > schedule_timeout+0x1db/0x2a0 kernel/time/timer.c:1854 > > do_wait_for_common kernel/sched/completion.c:85 [inline] > > __wait_for_common kernel/sched/completion.c:106 [inline] > > wait_for_common kernel/sched/completion.c:117 [inline] > > wait_for_completion+0x176/0x280 kernel/sched/completion.c:138 > > __do_sys_io_destroy fs/aio.c:1402 [inline] > > __se_sys_io_destroy fs/aio.c:1380 [inline] > > __x64_sys_io_destroy+0x17e/0x1e0 fs/aio.c:1380 > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > The reproducer is creating a thread, issuing a IOCB_CMD_PREAD from a > pipe in that thread, and then calling io_destroy from another thread. > Because there is no writer on the other end of the pipe, the read will > block. Note that it also is not submitted asynchronously, as that's not > supported. > > io_destroy is "hanging" because it's waiting for the read to finish. If > the read thread is killed, cleanup happens as usual. I'm not sure I > could classify this as a kernel bug. Hi Jeff, Thanks for looking into this. I suspect the reproducer may create a fork bomb that DoSed the kernel so that it can't make progress for 140 seconds. FTR, I've added it to https://github.com/google/syzkaller/issues/498#issuecomment-895071514 to take a closer look.
