Re: [PATCH] sysrq: Use SEND_SIG_FORCED instead of force_sig()
From: Andrew Morton
Date: Mon Mar 26 2012 - 18:43:20 EST
On Sat, 24 Mar 2012 15:00:24 +0400
Anton Vorontsov <anton.vorontsov@xxxxxxxxxx> 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
> 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.
> > 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@xxxxxxxxxx>
> Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
> 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))
> - force_sig(sig, p);
> + do_send_sig_info(sig, SEND_SIG_FORCED, p, true);
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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