Re: INFO: rcu detected stall in ndisc_alloc_skb

[Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>]

On 2019/01/19 21:16, Dmitry Vyukov wrote:
>> The question for me is, whether sysbot can detect hash collision with different
>> syz-program lines before writing the hash value to /dev/kmsg, and retry by modifying
>> syz-program lines in order to get a new hash value until collision is avoided.
>> If it is difficult, simpler choice like current Unix time and PID could be used
>> instead...
> 
> Hummm, say, if you run syz-manager locally and report a bug, where
> will the webserver and database that allows to download all satellite
> info work? How long you need to keep this info and provide the web
> service? You will also need to pay and maintain the server for... how
> long? I don't see how this can work and how we can ask people to do
> this. This frankly looks like overly complex solution to a problem
> were simpler solutions will work. Keeping all info in a self-contained
> file looks like the only option to make it work reliably.
> It's also not possible to attribute kernel output to individual programs.

The first messages I want to look at is kernel output. Then, I look at
syz-program lines as needed. But current "a self-contained file" is
hard to find kernel output. Even if we keep both kernel output and
syz-program lines in a single file, we can improve readability by
splitting into kernel output section and syz-program section.

  # Kernel output section start
  [$(uptime)][$(caller_info)] executing program #0123456789abcdef0123456789abcdef
  [$(uptime)][$(caller_info)] $(kernel_messages_caused_by_0123456789abcdef0123456789abcdef_are_here)
  [$(uptime)][$(caller_info)] executing program #456789abcdef0123456789abcdef0123
  [$(uptime)][$(caller_info)] $(kernel_messages_caused_by_456789abcdef0123456789abcdef0123_and_0123456789abcdef0123456789abcdef_are_here)
  [$(uptime)][$(caller_info)] executing program #89abcdef0123456789abcdef01234567
  [$(uptime)][$(caller_info)] $(kernel_messages_caused_by_89abcdef0123456789abcdef01234567_456789abcdef0123456789abcdef0123_and_0123456789abcdef0123456789abcdef_are_here)
  [$(uptime)][$(caller_info)] BUG: unable to handle kernel paging request at $(address)
  [$(uptime)][$(caller_info)] CPU: $(cpu) PID: $(pid) Comm: syz#89abcdef0123 Not tainted $(version) #$(build)
  [$(uptime)][$(caller_info)] $(backtrace_of_caller_info_is_here)
  [$(uptime)][$(caller_info)] Kernel panic - not syncing: Fatal exception
  # Kernel output section end
  # syzbot code section start
  Program for #0123456789abcdef0123456789abcdef
  $(program_lines_for_0123456789abcdef0123456789abcdef_is_here)
  Program for #456789abcdef0123456789abcdef0123
  $(program_lines_for_456789abcdef0123456789abcdef0123_is_here)
  Program for #89abcdef0123456789abcdef01234567
  $(program_lines_for_89abcdef0123456789abcdef01234567_is_here)
  # syzbot code section end