Re: [PATCH] show message when exceeded rlimit of pending signals

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 31 Oct 2009 17:50:14 +0900 Naohiro Ooiwa <nooiwa@miraclelinux.com> wrote:

> Naohiro Ooiwa wrote:
> > Andrew Morton wrote:
> >> On Fri, 30 Oct 2009 20:36:31 +0900
> >> Naohiro Ooiwa <nooiwa@miraclelinux.com> wrote:
> >>>
> >>> +static void show_reach_rlimit_sigpending(void)
> >>> +{
> >>> +	if (!printk_ratelimit())
> >>> +		return;
> >> printk_ratelimit() is a bad thing and we should be working toward
> >> removing it altogether, not adding new callers.
> >>
> >> Because it uses global state.  So if subsystem A is trying to generate
> >> lots of printk's, subsystem B's important message might get
> >> accidentally suppressed.
> >>
> >> It's better to use DEFINE_RATELIMIT_STATE() and __ratelimit() directly.
> > 
> > 
> > Thank you for your advices.
> > And I was glad to talk to you in Japan Linux Symposium.
> > 
> > I got it, now that you mention it.
> > I will fix my patch.
> > 
> >>> +	printk(KERN_INFO "%s/%d: reached the limit of pending signals.\n",
> >>> +				current->comm, current->pid);
> >> I suggest that this be
> >>
> >> 	"reached RLIMIT_SIGPENDING"
> >>
> >> because RLIMIT_SIGPENDING is a well-understood term and concept.
> >>
> > 
> > OK, I see.
> 
> I fixed my patch.
> Could you please check it.
> 

Please always include the full changelog and signoff with each
iteration of a patch.  That changelog might of course need updating as
the patch changes.


> ---
>  Documentation/kernel-parameters.txt |   11 +++++++++--
>  kernel/signal.c                     |   21 ++++++++++++++++++---
>  2 files changed, 27 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt
> b/Documentation/kernel-parameters.txt
> index 9107b38..3bbd92f 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2032,8 +2032,15 @@ and is between 256 and 4096 characters. It is defined in
> the file
> 
>  	print-fatal-signals=
>  			[KNL] debug: print fatal signals
> -			print-fatal-signals=1: print segfault info to
> -			the kernel console.
> +
> +			If enabled, warn about various signal handling
> +			related application anomalies: too many signals,
> +			too many POSIX.1 timers, fatal signals causing a
> +			coredump - etc.
> +
> +			If you hit the warning due to signal overflow,
> +			you might want to try "ulimit -i unlimited".
> +
>  			default: off.
> 
>  	printk.time=	Show timing data prefixed to each printk message line
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 6705320..624a626 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -41,6 +41,8 @@
> 
>  static struct kmem_cache *sigqueue_cachep;
> 
> +int print_fatal_signals __read_mostly;
> +
>  static void __user *sig_handler(struct task_struct *t, int sig)
>  {
>  	return t->sighand->action[sig - 1].sa.sa_handler;
> @@ -188,6 +190,17 @@ int next_signal(struct sigpending *pending, sigset_t *mask)
>  	return sig;
>  }
> 
> +static void show_reach_rlimit_sigpending(void)
> +{
> +	DEFINE_RATELIMIT_STATE(printk_rl_state, 5 * HZ, 10);

This needs to have `static' storage.  This bug should have been
apparent in your testing?

> +	if (!__ratelimit(&printk_rl_state))
> +		return;
> +
> +	printk(KERN_INFO "%s/%d: reached RLIMIT_SIGPENDING.\n",
> +				current->comm, current->pid);
> +}
> ...
>