linux-kernel - Re: INFO: task hung in filemap

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Message-Id: <201801152338.EBJ73933.FLSJHFVtOFOOQM@I-love.SAKURA.ne.jp>
Date:   Mon, 15 Jan 2018 23:38:26 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     dvyukov@...gle.com
Cc:     bot+980f5e5fc060c37505bd65abb49a963518b269d9@...kaller.appspotmail.com,
        ak@...ux.intel.com, akpm@...ux-foundation.org, jack@...e.cz,
        jlayton@...hat.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mgorman@...hsingularity.net, mingo@...nel.org,
        npiggin@...il.com, rgoldwyn@...e.com,
        syzkaller-bugs@...glegroups.com, axboe@...nel.dk,
        tom.leiming@...il.com, hare@...e.de, osandov@...com, shli@...com
Subject: Re: INFO: task hung in filemap_fault

Dmitry Vyukov wrote:
> On Mon, Jan 15, 2018 at 3:25 PM, Tetsuo Handa
> <penguin-kernel@...ove.sakura.ne.jp> wrote:
> > Dmitry Vyukov wrote:
> >> >> I am not completely following. You previously mentioned raw.log, which
> >> >> is a collection of multiple programs, but now you seem to be talking
> >> >> about a single reproducer. When syzbot manages to reproduce the bug
> >> >> only with syzkaller program but not with a corresponding C program, it
> >> >> provides only syzkaller program. It such case it can sense to convert.
> >> >> But the case you pointed to actually contains C program. So there is
> >> >> no need to do the conversion at all... What am I missing?
> >> >>
> >> >
> >> > raw.log is not readable for me.
> >> > I want to see C program even if syzbot did not manage to reproduce the bug.
> >> > If C program is available, everyone can try reproducing the bug with manually
> >> > trimmed C program.
> >>
> >> If it did not manage to reproduce the bug, there is no C program.
> >> There is no program at all.
> >>
> >
> > What!? Then, what does raw.log contain? I want to read raw.log as C program.
> 
> 
> raw.log is not a _program_, it's hundreds of separate programs that
> were executed before the crash.

I want to know the hundreds of separate programs as C programs.
Even if there are hundreds, more recently ran programs tend to be
the culprit.

>                                 It's also very compressed
> representation as compared to equivalent C programs. For example for
> this program:
> 
> mmap(&(0x7f0000000000/0xfff000)=nil, 0xfff000, 0x3, 0x32,
> 0xffffffffffffffff, 0x0)
> r0 = socket$nl_generic(0x10, 0x3, 0x10)
> sendmsg$nl_generic(r0,
> &(0x7f0000b3e000-0x38)={&(0x7f0000d4a000-0xc)={0x10, 0x0, 0x0, 0x0},
> 0xc, &(0x7f0000007000)={&(0x7f0000f7c000-0x15c)={0x24, 0x1c, 0x109,
> 0xffffffffffffffff, 0xffffffffffffffff, {0x4, 0x0, 0x0},
> [@nested={0x10, 0x9, [@typed={0xc, 0x0, @u32=0x0}]}]}, 0x24}, 0x1,
> 0x0, 0x0, 0x0}, 0x0)
> 
> you can get up to this amount of C code:
> https://gist.githubusercontent.com/dvyukov/eeaeb4e4ac45c3a251f72098c9295bf9/raw/700cd583507eca90711ba11b42e406f317553371/gistfile1.txt
> 
> that is, 700 lines of C source for 3 line program. So instead of a 1MB
> file that will be 100MB, and then it probably should be a gzip archive
> with hundreds of separate C files. There are people on this list
> complaining even about 200K of attachments. I don't see that this will
> be better and well accepted.
> 

I don't think attaching to mails is acceptable. Thus, I suggest e.g. CGI
service so that only those who want to try can obtain the C programs.