[PATCH] extend print_fatal_signals for reached RLIMIT_SIGP..

External Since: Nov 20, 2008 Posts: 3

When the system has too many timers or too many aggregate
queued signals, the EAGAIN error is returned to application
from kernel, including timer_create().
It means that exceeded limit of pending signals at all.
But we can't imagine it.

This patch show the message when reached limit of pending signals
and enabled print_fatal_signals.
If you see this message and your system behaved unexpectedly,
you can run following command.
# ulimit -i unlimited

With help from Hiroshi Shimamoto <h-shimamoto.TakeThisOut@ct.jp.nec.com>.

Signed-off-by: Naohiro Ooiwa <nooiwa.TakeThisOut@miraclelinux.com>
Acked-by: Ingo Molnar <mingo.TakeThisOut@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..56e9c00 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)
+{
+ static 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",
-- 1.5.4.1
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External Since: Nov 05, 2003 Posts: 2922

* Naohiro Ooiwa <nooiwa.DeleteThis@miraclelinux.com> wrote:

> When the system has too many timers or too many aggregate
> queued signals, the EAGAIN error is returned to application
> from kernel, including timer_create().
> It means that exceeded limit of pending signals at all.
> But we can't imagine it.
>
> This patch show the message when reached limit of pending signals
> and enabled print_fatal_signals.
> If you see this message and your system behaved unexpectedly,
> you can run following command.
> # ulimit -i unlimited
>
> With help from Hiroshi Shimamoto <h-shimamoto.DeleteThis@ct.jp.nec.com>.
>
>
> Signed-off-by: Naohiro Ooiwa <nooiwa.DeleteThis@miraclelinux.com>
> Acked-by: Ingo Molnar <mingo.DeleteThis@elte.hu>
> ---
> Documentation/kernel-parameters.txt | 11 +++++++++--
> kernel/signal.c | 21 ++++++++++++++++++---
> 2 files changed, 27 insertions(+), 5 deletions(-)

Thanks, i've applied your patch to tip:core/signal, for v2.6.33 merge
(if it passes all tests).

I made a few (very small) changes, see the -tip commit notification
email in this thread with the final commit:

- Extended the functions so that we can print which precise signal got
dropped - app writers will likely want to know that

- Changed the message to:

task/1234: reached RLIMIT_SIGPENDING, dropping signal

which is slightly more informative.

- Cleaned up small cleanliness details in surrounding code that caught
my eyes.

- Changed a few variable and function names to be a tiny bit more
expressive.

- Pushed the print_fatal_printks check into the new utility function
(print_dropped_signal()), to not clutter __sigqueue_alloc()
needlessly.

- Clarified the commit log message a bit, gave sample output of the new
behavior.

Thanks,

Ingo
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