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    SubjectRe: INFO: task hung in __io_uring_files_cancel
    Date
    On 22/11/2020 03:04, Hillf Danton wrote:
    > On Sat, 21 Nov 2020 14:35:15 -0800
    >> syzbot found the following issue on:
    >>
    >> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10401726500000
    >> final oops: https://syzkaller.appspot.com/x/report.txt?x=12401726500000
    >> console output: https://syzkaller.appspot.com/x/log.txt?x=14401726500000
    >>
    >> IMPORTANT: if you fix the issue, please add the following tag to the commit:
    >> Reported-by: syzbot+c0d52d0b3c0c3ffb9525@syzkaller.appspotmail.com
    >> Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion")
    >>
    >> INFO: task syz-executor.0:9557 blocked for more than 143 seconds.
    >> Not tainted 5.10.0-rc4-next-20201117-syzkaller #0
    >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    >> task:syz-executor.0 state:D stack:28584 pid: 9557 ppid: 8485 flags:0x00004002
    >> Call Trace:
    >> context_switch kernel/sched/core.c:4269 [inline]
    >> __schedule+0x890/0x2030 kernel/sched/core.c:5019
    >> schedule+0xcf/0x270 kernel/sched/core.c:5098
    >> io_uring_cancel_files fs/io_uring.c:8720 [inline]
    >> io_uring_cancel_task_requests fs/io_uring.c:8772 [inline]
    >> __io_uring_files_cancel+0xc4d/0x14b0 fs/io_uring.c:8868
    >> io_uring_files_cancel include/linux/io_uring.h:51 [inline]
    >> exit_files+0xe4/0x170 fs/file.c:456
    >> do_exit+0xb61/0x29f0 kernel/exit.c:818
    >> do_group_exit+0x125/0x310 kernel/exit.c:920
    >> get_signal+0x3ea/0x1f70 kernel/signal.c:2750
    >> arch_do_signal_or_restart+0x2a6/0x1ea0 arch/x86/kernel/signal.c:811
    >> handle_signal_work kernel/entry/common.c:145 [inline]
    >> exit_to_user_mode_loop kernel/entry/common.c:169 [inline]
    >> exit_to_user_mode_prepare+0x124/0x200 kernel/entry/common.c:199
    >> syscall_exit_to_user_mode+0x38/0x260 kernel/entry/common.c:274
    >> entry_SYSCALL_64_after_hwframe+0x44/0xa9
    >> RIP: 0033:0x45deb9
    >> Code: Unable to access opcode bytes at RIP 0x45de8f.
    >> RSP: 002b:00007fa68397ccf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
    >> RAX: fffffffffffffe00 RBX: 000000000118bf28 RCX: 000000000045deb9
    >> RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000118bf28
    >> RBP: 000000000118bf20 R08: 0000000000000000 R09: 0000000000000000
    >> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
    >> R13: 00007fff50acc9af R14: 00007fa68397d9c0 R15: 000000000118bf2c
    >>
    ...
    >
    > Fix 311daef8013a ("io_uring: replace inflight_wait with tctx->wait")
    > by cutting the pre-condition to wakeup because waitqueue_active()
    > speaks the language in the East End while atomic_read() may speak
    > the language in Paris.

    Your description doesn't help, why do you think this is the problem?
    ->in_idle is always set when io_uring_cancel_files() sleeps on it,
    and ->inflight_lock should guarantee ordering.

    >
    > --- a/fs/io_uring.c
    > +++ b/fs/io_uring.c
    > @@ -6082,8 +6082,7 @@ static void io_req_drop_files(struct io_
    >
    > spin_lock_irqsave(&ctx->inflight_lock, flags);
    > list_del(&req->inflight_entry);
    > - if (atomic_read(&tctx->in_idle))
    > - wake_up(&tctx->wait);
    > + wake_up(&tctx->wait);
    > spin_unlock_irqrestore(&ctx->inflight_lock, flags);
    > req->flags &= ~REQ_F_INFLIGHT;
    > put_files_struct(req->work.identity->files);
    >

    --
    Pavel Begunkov

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