[PATCH] ppc32: Kill init on unhandled synchronous signals

This is a patch that I have had in my tree for ages.  If init causes
an exception that raises a signal, such as a SIGSEGV, SIGILL or
SIGFPE, and it hasn't registered a handler for it, we don't deliver
the signal, since init doesn't get any signals that it doesn't have a
handler for.  But that means that we just return to userland and
generate the same exception again immediately.  With this patch we
print a message and kill init in this situation.

This is very useful when you have a bug in the kernel that means that
init doesn't get as far as executing its first instruction. :)
Without this patch the system hangs when it gets to starting the
userland init; with it you at least get a message giving you a clue
about what has gone wrong.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 23 insertions, 5 deletions

diff --git a/arch/ppc/kernel/traps.c b/arch/ppc/kernel/traps.c
index 8356d544fa60..961ede87be72 100644
--- a/arch/ppc/kernel/traps.c
+++ b/arch/ppc/kernel/traps.c
@@ -118,6 +118,28 @@ void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
         info.si_code = code;
         info.si_addr = (void __user *) addr;
         force_sig_info(signr, &info, current);
+
+        /*
+         * Init gets no signals that it doesn't have a handler for.
+         * That's all very well, but if it has caused a synchronous
+         * exception and we ignore the resulting signal, it will just
+         * generate the same exception over and over again and we get
+         * nowhere.  Better to kill it and let the kernel panic.
+         */
+        if (current->pid == 1) {
+                __sighandler_t handler;
+
+                spin_lock_irq(&current->sighand->siglock);
+                handler = current->sighand->action[signr-1].sa.sa_handler;
+                spin_unlock_irq(&current->sighand->siglock);
+                if (handler == SIG_DFL) {
+                        /* init has generated a synchronous exception
+                           and it doesn't have a handler for the signal */
+                        printk(KERN_CRIT "init has generated signal %d "
+                               "but has no handler for it\n", signr);
+                        do_exit(signr);
+                }
+        }
 }
 
 /*
diff --git a/arch/ppc/mm/fault.c b/arch/ppc/mm/fault.c
index 57d9930843ac..ee5e9f25baf9 100644
--- a/arch/ppc/mm/fault.c
+++ b/arch/ppc/mm/fault.c
@@ -278,11 +278,7 @@ bad_area:
 
         /* User mode accesses cause a SIGSEGV */
         if (user_mode(regs)) {
-                info.si_signo = SIGSEGV;
-                info.si_errno = 0;
-                info.si_code = code;
-                info.si_addr = (void __user *) address;
-                force_sig_info(SIGSEGV, &info, current);
+                _exception(SIGSEGV, regs, code, address);
                 return 0;
         }