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SubjectRe: [syzbot] INFO: rcu detected stall in sys_recvmmsg
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On Tue, 2021-09-21 at 17:13 -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 1f77990c4b79 Add linux-next specific files for 20210920
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1383891d300000
> kernel config: https://syzkaller.appspot.com/x/.config?x=ab1346371f2e6884
> dashboard link: https://syzkaller.appspot.com/bug?extid=3360da629681aa0d22fe
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1625f1ab300000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17eb1b3b300000
>
> The issue was bisected to:
>
> commit 020250f31c4c75ac7687a673e29c00786582a5f4
> Author: Dmitry Kadashev <dkadashev@gmail.com>
> Date: Thu Jul 8 06:34:43 2021 +0000
>
> namei: make do_linkat() take struct filename
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15f5ef77300000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=17f5ef77300000
> console output: https://syzkaller.appspot.com/x/log.txt?x=13f5ef77300000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3360da629681aa0d22fe@syzkaller.appspotmail.com
> Fixes: 020250f31c4c ("namei: make do_linkat() take struct filename")

I'm unsure why the bisection points to this commit. This looks like an
MPTCP specific issue, due to bad handling of MSG_WAITALL recvmsg()
flag.

I'll test a fix with syzbot to confirm the above.

Cheers,

Paolo

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