On 22/11/2020 09:20, Hillf Danton wrote: > On Sun, 22 Nov 2020 03:32:01 +0000 Pavel Begunkov wrote: >> 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@xxxxxxxxxxxxxxxxxxxxxxxxx >>>> 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, > > That is what I could find to describe the changs added in > 311daef8013a, given that waitqueue_active() and atomic_read() IMO are > primary bricks without natural links prebuilt. I dont think either > of them could be replaced with another even in 311daef8013a. There are not linked, but that doesn't make it automatically wrong. I still don't understand how it fixes the problem, and it's better to find the root cause because there are similar places that might still be similarly flawed. >> why do you think this is the problem? > > This is not a tough question, thanks to the reproducer. > >> ->in_idle is always set when io_uring_cancel_files() sleeps on it, >> and ->inflight_lock should guarantee ordering. > > The syzbot report makes sense, right? > >>> >>> --- 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
