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From:   Michael Stapelberg <michael+lkml@stapelberg.ch>
Date:   Wed, 12 Feb 2020 10:38:33 +0100
Message-ID: <CANnVG6=s1C7LSDGD1-Ato-sfaKi1LQvW3GM5wfAiUqWXibEohw@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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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?

On Wed, Feb 12, 2020 at 9:34 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> On Wed, Feb 12, 2020 at 8:58 AM Michael Stapelberg
> <michael+lkml@stapelberg.ch> wrote:
>
> > (gdb) p *req->args
> > $5 =3D {
> >   nodeid =3D 18446683600620026424,
> >   opcode =3D 2167928246,
> >   in_numargs =3D 65535,
> >   out_numargs =3D 65535,
> >   force =3D false,
> >   noreply =3D false,
> >   nocreds =3D false,
> >   in_pages =3D false,
> >   out_pages =3D false,
> >   out_argvar =3D true,
> >   page_zeroing =3D true,
> >   page_replace =3D false,
> >   in_args =3D {{
> >       size =3D 978828800,
> >       value =3D 0x2fafce0
> >     }, {
> >       size =3D 978992728,
> >       value =3D 0xffffffff8138efaa <fuse_alloc_forget+26>
> >     }, {
> >       size =3D 50002688,
> >       value =3D 0xffffffff8138635f <fuse_lookup_name+255>
> >     }},
> >   out_args =3D {{
> >       size =3D 570,
> >       value =3D 0xffffc90002fafb10
> >     }, {
> >       size =3D 6876,
> >       value =3D 0x3000000001adc
> >     }},
> >   end =3D 0x1000100000001
> > }
>
> Okay, that looks like rubbish, the request was possibly freed and overwri=
tten.
>
> > Independently, as a separate test, I have also modified the source like=
 this:
> >
> > bool async;
> > bool async_early =3D req->args->end;
> >
> > if (test_and_set_bit(FR_FINISHED, &req->flags))
> > goto put_request;
> >
> > async =3D req->args->end;
> >
> > =E2=80=A6and printed the value of async and async_early. async is true,
> > async_early is false.
>
> Can you save and print out the value of req->opcode before the
> test_and_set_bit()?
>
> Thanks,
> Miklos