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

[Naohiro Ooiwa]

Hi Ingo,

> Here's a slightly improved version of the text:

Thank you for your review and collect my English.

>> +int print_fatal_signals;
>
> i'd suggest __read_mostly.

> Plus please move variables to the top of the file. (i know this comes
> from the previous code but we can improve it while we are touching it)

Of course. You're right, if we found one like it,
I want to improve the code little by little too.

How is the following patch.

Signed-off-by: Naohiro Ooiwa <nooiwa@xxxxxxxxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
---
 Documentation/kernel-parameters.txt |   13 ++++++++++---
 kernel/signal.c                     |   16 +++++++++++++---
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9107b38..8492ad3 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2032,9 +2032,16 @@ 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.
-			default: off.
+
+ 			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
 			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
diff --git a/kernel/signal.c b/kernel/signal.c
index 6705320..c913eb7 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 +190,12 @@ int next_signal(struct sigpending *pending, sigset_t *mask)
 	return sig;
 }

+static void show_reach_rlimit_sigpending(void)
+{
+	if (printk_ratelimit())
+		printk(KERN_WARNING "%s/%d: reached the limit of pending signals.\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 +217,12 @@ 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 +937,6 @@ 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",
-- 1.5.4.1


Ingo Molnar wrote:
> * Naohiro Ooiwa <nooiwa@xxxxxxxxxxxxxxxx> wrote:
> 
>> Hi Ingo,
>>
>> Now that you mention it, I think so, too.
>> I update my patch.
>>
>> How is the following patch.
>> Could you please review it.
>>
>> Thanks you.
>> Naohiro Ooiwa
>>
>>
>>
>> Signed-off-by: Naohiro Ooiwa <nooiwa@xxxxxxxxxxxxxxxx>
>> ---
>>  Documentation/kernel-parameters.txt |    9 ++++++++-
>>  kernel/signal.c                     |   16 +++++++++++++---
>>  2 files changed, 21 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt
>> b/Documentation/kernel-parameters.txt
>> index 9107b38..01c2723 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
>> +			If you would like to know what the cause of a coredump
>> +			by signal number, if your working system may have
>> +			too many POSIX.1 timers, and when during the system
>> +			test,you may as well to enable this parameter.
>>  			print-fatal-signals=1: print segfault info to
>> -			the kernel console.
>> +			the kernel console, and print caution that reached the
>> +			limit of pending signals to the kernel console.
>> +			When printed the caution messages, you can try
>> +			"ulimit -i unlimited".
>>  			default: off.
>>
> 
> Here's a slightly improved version of the text:
> 
>  	print-fatal-signals=
>  			[KNL] debug: print fatal signals
> 
> 			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.
> 
>> +int print_fatal_signals;
> 
> i'd suggest __read_mostly.
> 
> Plus please move variables to the top of the file. (i know this comes 
> from the previous code but we can improve it while we are touching it)
> 
> With these things addressed it looks good to me:
> 
> Acked-by: Ingo Molnar <mingo@xxxxxxx>
> 
> 	Ingo
> 

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