On 2019/05/16 20:57, Petr Mladek wrote: > CCed Stephen to discuss linux-next related question at the bottom > of the mail. > > On Thu 2019-05-16 17:19:12, Tetsuo Handa wrote: >> On 2019/05/15 19:55, Petr Mladek wrote: >> But in the context of syzbot's testing where there are only 2 CPUs >> in the target VM (which means that only small number of threads and >> not so much memory) and threads get SIGKILL after 5 seconds from fork(), >> being unable to reach do_exit() within 10 seconds is likely a sign of >> something went wrong. For example, 6 out of 7 trials of a reproducer for >> https://syzkaller.appspot.com/bug?id=835a0b9e75b14b55112661cbc61ca8b8f0edf767 >> resulted in "no output from test machine" rather than "task hung". >> This patch is revealing that such killed threads are failing to reach >> do_exit() because they are trapped at unkillable retry loop due to a >> race bug. >> >> Therefore, I would like to try this patch in linux-next.git for feasibility >> testing whether this patch helps finding more bugs and reproducers for such >> bugs, by bringing "unable to terminate threads" reports out of "no output >> from >> test machine" reports. We can add sysctl settings before sending to >> linux.git. > > In this case, the watchdog should get enabled on with > CONFIG_DEBUG_AID_FOR_SYZBOT
Since "[PATCH] printk: Monitor change of console loglevel." is one time (only needed until we find the reason of silence), testing on only linux-next.git is sufficient and it gets enabled on with CONFIG_DEBUG_AID_FOR_SYZBOT. > > Also we should ask/inform Stephen about this. I am not sure > if he is willing to resolve eventual conflicts for these > syzboot-specific patches that are not upstream candidates. > > A solution might be to create sysbot-specific for-next branch > that Stephen might simply ignore when there are conflicts. > And you would be responsible for updating it. syzbot tests not only linux-next.git but also various trees, and tests attempted depends on target git tree. Therefore, apart from whether we can introduce a kernel config option for fuzzing testing, "[PATCH] kernel/hung_task.c: Monitor killed tasks." is expected to be in linux.git. This patch will eventually become upstream candidate.