Messages in this thread Patch in this message |  | | | Date | Wed, 15 Feb 2012 02:50:17 +0400 | | From | Anton Vorontsov <> | | Subject | [PATCH] sysrq: Use SEND_SIG_FORCED instead of force_sig() |
| |
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.
Suggested-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org> --- On Fri, Feb 10, 2012 at 09:10:08PM +0100, Oleg Nesterov wrote: > > --- a/drivers/tty/sysrq.c > > +++ b/drivers/tty/sysrq.c > > @@ -324,9 +324,12 @@ static void send_sig_all(int sig) > > > > read_lock(&tasklist_lock); > > for_each_process(p) { > > - if (p->mm && !is_global_init(p)) > > - /* Not swapper, init nor kernel thread */ > > - force_sig(sig, p); > > + if (p->flags & PF_KTHREAD) > > + continue; > > + if (is_global_init(p)) > > + continue; > > + > > + force_sig(sig, p); > > } > > read_unlock(&tasklist_lock); > > Obviously I agree with this change. > > But where does this read_lock(tasklist) come from?
It came from this patch: http://lkml.org/lkml/2012/2/7/24
> We discussed this with Anton. Yes, tasklist ensures that > force_sig() can't crash the kernel. But it is still wrong > and should not be used. > > I think send_sig_all() should use SEND_SIG_FORCED (this > depends on the patches I sent to Andrew), in this case > tasklist is not needed.
Well, I think the lock is still a good thing: we don't want any new processes to be created while we kill others.
I might be wrong, but copy_process() issues recalc_sigpending() under tasklist lock especially the for this scenario.
So, in this and in OOM cases we have to be precise (unlike LMK). Sysrq is a rare thing, so there is actually should be no problem with holding the lock.
So, how about this patch?
Greg, can we take it via -mm tree, as it depends on a few sched patches?
drivers/tty/sysrq.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) 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); } -- 1.7.7.6
|  |