x86: i386-show-unhandled-signals-v3

This patch makes the i386 behave the same way that x86_64 does when a
segfault happens.  A line gets printed to the kernel log so that tools
that need to check for failures can behave more uniformly between
debug.show_unhandled_signals sysctl variable to 0 (or by doing echo 0 >
/proc/sys/debug/exception-trace)

Also, all of the lines being printed are now using printk_ratelimit() to
deny the ability of DoS from a local user with a program like the
following:

main()
{
       while (1)
               if (!fork()) *(int *)0 = 0;
}

This new revision also includes the fix that Andrew did which got rid of
new sysctl that was added to the system in earlier versions of this.
Also, 'show-unhandled-signals' sysctl has been renamed back to the old
'exception-trace' to avoid breakage of people's scripts.

AK: Enabling by default for i386 will be likely controversal, but let's see what happens
AK: Really folks, before complaining just fix your segfaults
AK: I bet this will find a lot of silent issues

Signed-off-by: Masoud Sharbiani <masouds@google.com>
Signed-off-by: Andi Kleen <ak@suse.de>
[ Personally, I've found the complaints useful on x86-64, so I'm all for
  this. That said, I wonder if we could do it more prettily..   -Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/signal.h b/include/linux/signal.h
index ea91abe..0ae3388 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -237,12 +237,15 @@ extern int group_send_sig_info(int sig, struct siginfo *info, struct task_struct
 extern int __group_send_sig_info(int, struct siginfo *, struct task_struct *);
 extern long do_sigpending(void __user *, unsigned long);
 extern int sigprocmask(int, sigset_t *, sigset_t *);
+extern int show_unhandled_signals;
 
 struct pt_regs;
 extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
 
 extern struct kmem_cache *sighand_cachep;
 
+int unhandled_signal(struct task_struct *tsk, int sig);
+
 /*
  * In POSIX a signal is sent either to a specific thread (Linux task)
  * or to the process as a whole (Linux thread group).  How the signal