Messages in this thread | | | Date | Mon, 17 Mar 2014 21:19:19 +0100 | From | Oleg Nesterov <> | Subject | Re: [v3.13][v3.14][Regression] kthread: make kthread_create() killable |
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On 03/17, Andrew Morton wrote: > > On Fri, 14 Mar 2014 16:46:26 -0400 Joseph Salisbury <joseph.salisbury@canonical.com> wrote: > > > Hi Tetsuo, > > > > A kernel bug report was opened against Ubuntu[0]. We performed a kernel > > bisect, and found that reverting the following commit resolved this bug: > > > > > > commit 786235eeba0e1e85e5cbbb9f97d1087ad03dfa21 > > Author: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > > Date: Tue Nov 12 15:06:45 2013 -0800 > > > > kthread: make kthread_create() killable > > > > The regression was introduced as of v3.13-rc1. > > > > The bug indicates an issue with the SAS controller during > > initialization, which prevents the system from booting. Additional > > details are available in the bug report or on request. > > > > I was hoping to get your feedback, since you are the patch author. Do > > you think gathering any additional data will help diagnose this issue, > > or would it be best to submit a revert request? > > > > [0] http://pad.lv/1276705 > > What process is running here? Presumably modprobe. > > A possible explanation is that modprobe has genuinely received a > SIGKILL. Can you identify anything in this setup which might send a > SIGKILL to the modprobe process?
See also other discussion in this thread, I thinks the code in drivers/ is buggy anyway.
> kthread_create_on_node() thinks that SIGKILL came from the oom-killer > and it cheerfully returns -ENOMEM, which is incorrect if that signal > came from userspace.
Yes, I think it should return -EINTR.
> And I don't _think_ we prevent > userspace-originated signals from unblocking > wait_for_completion_killable()?
And we should not.
> Root cause time: it's wrong for the oom-killer to use SIGKILL.
Not sure... what else?
> In fact > it's basically always wrong to send signals from in-kernel.
Well, SIGSEGV, SIGIO...
> Signals > are a userspace IPC mechanism and using them in-kernel a) makes it hard > (or impossible) to distinguish them from userspace-originated signals > and b) permits userspace to produce surprising results in the kernel, > which I suspect is what we're seeing here.
Well, I think in this case it doesn't matter who/why sends a signal. The task is killed, it should react and exit asap. And kthread_create() can fail in any case, at least the kernel should not crash.
Oleg.
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