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

Naohiro Ooiwa
2009-10-31T08:50:22Z

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.

Thanks you.
Naohiro Ooiwa

Signed-off-by: Naohiro Ooiwa <nooiwa@miraclelinux.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
---
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);
+
+ if (!__ratelimit(&printk_rl_state))
+ return;
+
+ printk(KERN_INFO "%s/%d: reached RLIMIT_SIGPENDING.\n",
+ current->comm, current->pid);
+}
+
/*
* allocate a new signal queue record
* - this may be called without locks if and only if t == current, otherwise an
@@ -209,8 +222,12 @@ static struct sigqueue *__sigqueue_alloc(struct task_struct
*t, gfp_t flags,
atomic_inc(&user->sigpending);
if (override_rlimit ||
atomic_read(&user->sigpending) <=
- t->signal->rlim[RLIMIT_SIGPENDING].rlim_cur)
+ t->signal->rlim[RLIMIT_SIGPENDING].rlim_cur) {
q = kmem_cache_alloc(sigqueue_cachep, flags);
+ } else {
+ if (print_fatal_signals)
+ show_reach_rlimit_sigpending();
+ }
if (unlikely(q == NULL)) {
atomic_dec(&user->sigpending);
free_uid(user);
@@ -925,8 +942,6 @@ static int send_signal(int sig, struct siginfo *info, struct
task_struct *t,
return __send_signal(sig, info, t, group, from_ancestor_ns);
}

-int print_fatal_signals;
-
static void print_fatal_signal(struct pt_regs *regs, int signr)
{
printk("%s/%d: potentially unexpected fatal signal %d.\n",