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

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Message-Id: <201801081948.HAE82801.FQOSHtMOFVLFOJ@I-love.SAKURA.ne.jp>
Date:   Mon, 8 Jan 2018 19:48:16 +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:
> >> Hi Tetsuo,
> >>
> >> syzbot always re-runs the same workload on a new machine. If it
> >> manages to reproduce the problem, it provides a reproducer. In this
> >> case it didn't.
> >
> > Even if it did not manage to reproduce the problem, showing raw.log in
> > C format is helpful for me. For example,
> >
> >   ioctl$LOOP_CHANGE_FD(r3, 0x4c00, r1)
> >
> > is confusing. 0x4c00 is not LOOP_CHANGE_FD but LOOP_SET_FD.
> > If the message were
> >
> >   ioctl(r3, 0x4c00, r1)
> >
> > more people will be able to read what the program tried to do.
> > There are many operations done on loop devices, but are too hard
> > for me to pick up only loop related actions.
> 
> 
> Hi Tetsuo,
> 
> The main purpose of this format is different, this is a complete
> representation of programs that allows replaying them using syzkaller
> tools.

What is ioctl$LOOP_CHANGE_FD(r3, 0x4c00, r1) ?
0x4c00 is LOOP_SET_FD. Why LOOP_CHANGE_FD is there?

>        We can't simply drop info from there. Do you propose to add
> another attached file that contains the same info in a different
> format? What is the exact format you are proposing?

Plain C program which can be compiled without installing additional
program/library packages (except those needed for building kernels).

>                                                     Is it just
> dropping the syscall name part after $ sign? Note that it's still not
> C, more complex syscall generally look as follows:
> 
> perf_event_open(&(0x7f0000b5a000)={0x4000000002, 0x78, 0x1e2, 0x0,
> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xffff, 0x0,
> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
> @perf_bp={&(0x7f0000000000)=0x0, 0x0}, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
> 0x0, 0x0}, 0x0, 0x0, 0xffffffffffffffff, 0x0)
> recvmmsg(0xffffffffffffffff, &(0x7f0000003000)=[{{0x0, 0x0,
> &(0x7f0000002000)=[{&(0x7f000000a000)=""/193, 0xc1},
> {&(0x7f0000007000-0x3d)=""/61, 0x3d}], 0x2,
> &(0x7f0000005000-0x67)=""/103, 0x67, 0x0}, 0x0}], 0x1, 0x0,
> &(0x7f0000003000-0x10)={0x77359400, 0x0})
> bpf$PROG_LOAD(0x5, &(0x7f0000000000)={0x1, 0x5,
> &(0x7f0000002000)=@...med={{0x18, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
> 0x0}, [@jmp={0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}], {0x95, 0x0, 0x0,
> 0x0}}, &(0x7f0000004000-0xa)='syzkaller\x00', 0x3, 0xc3,
> &(0x7f0000386000)=""/195, 0x0, 0x0, [0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
> 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0], 0x0}, 0x48)
> 
> Note: you can convert any syzkaller program to equivalent C code using
> syz-prog2c utility that comes with syzkaller.

I won't install go language into my environment for analyzing/reproducing your
reports. If syz-prog2c is provided as a CGI service (e.g. receive URL containing
raw.log and print the converted C program), I might try it.