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From:   Michael Stapelberg <michael+lkml@stapelberg.ch>
Date:   Thu, 13 Feb 2020 08:23:07 +0100
Message-ID: <CANnVG6=u8drSyKhF9Gjd-Y-saN8gdOSOsmEJenyWXsQE9QYmVQ@mail.gmail.com>
Subject: Re: Still a pretty bad time on 5.4.6 with fuse_request_end.
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     fuse-devel <fuse-devel@lists.sourceforge.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kyle Sanderson <kyle.leet@gmail.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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I confirm that the patch fixes the issue I was seeing. Thanks a lot!

On Wed, Feb 12, 2020 at 8:36 PM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Wed, Feb 12, 2020 at 10:38 AM Michael Stapelberg
> <michael+lkml@stapelberg.ch> wrote:
> >
> > Unfortunately not: when I change the code like so:
> >
> >     bool async;
> >     uint32_t opcode_early =3D req->args->opcode;
> >
> >     if (test_and_set_bit(FR_FINISHED, &req->flags))
> >         goto put_request;
> >
> >     async =3D req->args->end;
> >
> > =E2=80=A6gdb only reports:
> >
> > (gdb) bt
> > #0  0x000000a700000001 in ?? ()
> > #1  0xffffffff8137fc99 in fuse_copy_finish (cs=3D0x20000ffffffff) at
> > fs/fuse/dev.c:681
> > Backtrace stopped: previous frame inner to this frame (corrupt stack?)
> >
> > But maybe that=E2=80=99s a hint in and of itself?
>
> Yep, it's a stack use after return bug.   Attached patch should fix
> it, though I haven't tested it.
>
> Thanks,
> Miklos