Messages in this thread | | | Date | Mon, 26 Mar 2012 15:43:03 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] sysrq: Use SEND_SIG_FORCED instead of force_sig() |
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On Sat, 24 Mar 2012 15:00:24 +0400 Anton Vorontsov <anton.vorontsov@linaro.org> wrote:
> Change send_sig_all() to use do_send_sig_info(SEND_SIG_FORCED) > instead of force_sig(SIGKILL). With the recent changes we do not > need force_ to kill the CLONE_NEWPID tasks. > > And this is more correct. force_sig() can race with the exiting > thread, while do_send_sig_info(group => true) kill the whole > process. > > Some more notes from Oleg Nesterov: > > > Just one note. This change makes no difference for sysrq_handle_kill(). > > But it obviously changes the behaviour sysrq_handle_term(). I think > > this is fine, if you want to really kill the task which blocks/ignores > > SIGTERM you can use sysrq_handle_kill(). > > > > Even ignoring the reasons why force_sig() is simply wrong here, > > force_sig(SIGTERM) looks strange. The task won't be killed if it has > > a handler, but SIG_IGN can't help. However if it has the handler > > but blocks SIGTERM temporary (this is very common) it will be killed. > > Also, > > > force_sig() can't kill the process if the main thread has already > > exited. IOW, it is trivial to create the process which can't be > > killed by sysrq. > > So, this patch fixes the issue. > > Suggested-by: Oleg Nesterov <oleg@redhat.com> > Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Acked-by: Oleg Nesterov <oleg@redhat.com> > Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org> > --- > > The patch depends on a few Oleg's patches in -mm, so I believe > this should be -mm material as well. > > drivers/tty/sysrq.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c > index 8db9125..5ab8039 100644 > --- a/drivers/tty/sysrq.c > +++ b/drivers/tty/sysrq.c > @@ -329,7 +329,7 @@ static void send_sig_all(int sig) > if (is_global_init(p)) > continue; > > - force_sig(sig, p); > + do_send_sig_info(sig, SEND_SIG_FORCED, p, true); > } > read_unlock(&tasklist_lock); > }
It's unclear how serious this race is (I'm guessing "not very"), but this patch looks like 3.3 material anyway, yes?
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