lib/bug.c: use common WARN helper

The traceoff_on_warning option doesn't have any effect on s390, powerpc,
arm64, parisc, and sh because there are two different types of WARN
implementations:

1) The above mentioned architectures treat WARN() as a special case of a
   BUG() exception.  They handle warnings in report_bug() in lib/bug.c.

2) All other architectures just call warn_slowpath_*() directly.  Their
   warnings are handled in warn_slowpath_common() in kernel/panic.c.

Support traceoff_on_warning on all architectures and prevent any future
divergence by using a single common function to emit the warning.

Also remove the '()' from '%pS()', because the parentheses look funky:

  [   45.607629] WARNING: at /root/warn_mod/warn_mod.c:17 .init_dummy+0x20/0x40 [warn_mod]()

Reported-by: Chunyu Hu <chuhu@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Tested-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 34 insertions, 39 deletions

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index fdf6fa078422..f90588abbfd4 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -81,6 +81,12 @@ extern void warn_slowpath_null(const char *file, const int line);
         do { printk(arg); __WARN_TAINT(taint); } while (0)
 #endif
 
+/* used internally by panic.c */
+struct warn_args;
+
+void __warn(const char *file, int line, void *caller, unsigned taint,
+            struct pt_regs *regs, struct warn_args *args);
+
 #ifndef WARN_ON
 #define WARN_ON(condition) ({                                           \
         int __ret_warn_on = !!(condition);                              \
diff --git a/kernel/panic.c b/kernel/panic.c
index d96469de72dc..fa400852bf6c 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -24,6 +24,7 @@
 #include <linux/init.h>
 #include <linux/nmi.h>
 #include <linux/console.h>
+#include <linux/bug.h>
 
 #define PANIC_TIMER_STEP 100
 #define PANIC_BLINK_SPD 18
@@ -449,20 +450,25 @@ void oops_exit(void)
         kmsg_dump(KMSG_DUMP_OOPS);
 }
 
-#ifdef WANT_WARN_ON_SLOWPATH
-struct slowpath_args {
+struct warn_args {
         const char *fmt;
         va_list args;
 };
 
-static void warn_slowpath_common(const char *file, int line, void *caller,
-                                 unsigned taint, struct slowpath_args *args)
+void __warn(const char *file, int line, void *caller, unsigned taint,
+            struct pt_regs *regs, struct warn_args *args)
 {
         disable_trace_on_warning();
 
         pr_warn("------------[ cut here ]------------\n");
-        pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS()\n",
-                raw_smp_processor_id(), current->pid, file, line, caller);
+
+        if (file)
+                pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
+                        raw_smp_processor_id(), current->pid, file, line,
+                        caller);
+        else
+                pr_warn("WARNING: CPU: %d PID: %d at %pS\n",
+                        raw_smp_processor_id(), current->pid, caller);
 
         if (args)
                 vprintk(args->fmt, args->args);
@@ -479,20 +485,27 @@ static void warn_slowpath_common(const char *file, int line, void *caller,
         }
 
         print_modules();
-        dump_stack();
+
+        if (regs)
+                show_regs(regs);
+        else
+                dump_stack();
+
         print_oops_end_marker();
+
         /* Just a warning, don't kill lockdep. */
         add_taint(taint, LOCKDEP_STILL_OK);
 }
 
+#ifdef WANT_WARN_ON_SLOWPATH
 void warn_slowpath_fmt(const char *file, int line, const char *fmt, ...)
 {
-        struct slowpath_args args;
+        struct warn_args args;
 
         args.fmt = fmt;
         va_start(args.args, fmt);
-        warn_slowpath_common(file, line, __builtin_return_address(0),
-                             TAINT_WARN, &args);
+        __warn(file, line, __builtin_return_address(0), TAINT_WARN, NULL,
+               &args);
         va_end(args.args);
 }
 EXPORT_SYMBOL(warn_slowpath_fmt);
@@ -500,20 +513,18 @@ EXPORT_SYMBOL(warn_slowpath_fmt);
 void warn_slowpath_fmt_taint(const char *file, int line,
                              unsigned taint, const char *fmt, ...)
 {
-        struct slowpath_args args;
+        struct warn_args args;
 
         args.fmt = fmt;
         va_start(args.args, fmt);
-        warn_slowpath_common(file, line, __builtin_return_address(0),
-                             taint, &args);
+        __warn(file, line, __builtin_return_address(0), taint, NULL, &args);
         va_end(args.args);
 }
 EXPORT_SYMBOL(warn_slowpath_fmt_taint);
 
 void warn_slowpath_null(const char *file, int line)
 {
-        warn_slowpath_common(file, line, __builtin_return_address(0),
-                             TAINT_WARN, NULL);
+        __warn(file, line, __builtin_return_address(0), TAINT_WARN, NULL, NULL);
 }
 EXPORT_SYMBOL(warn_slowpath_null);
 #endif
diff --git a/lib/bug.c b/lib/bug.c
index 6cde380f09de..bc3656e944d2 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -167,30 +167,8 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 
         if (warning) {
                 /* this is a WARN_ON rather than BUG/BUG_ON */
-                pr_warn("------------[ cut here ]------------\n");
-
-                if (file)
-                        pr_warn("WARNING: at %s:%u\n", file, line);
-                else
-                        pr_warn("WARNING: at %p [verbose debug info unavailable]\n",
-                                (void *)bugaddr);
-
-                if (panic_on_warn) {
-                        /*
-                         * This thread may hit another WARN() in the panic path.
-                         * Resetting this prevents additional WARN() from
-                         * panicking the system on this thread.  Other threads
-                         * are blocked by the panic_mutex in panic().
-                         */
-                        panic_on_warn = 0;
-                        panic("panic_on_warn set ...\n");
-                }
-
-                print_modules();
-                show_regs(regs);
-                print_oops_end_marker();
-                /* Just a warning, don't kill lockdep. */
-                add_taint(BUG_GET_TAINT(bug), LOCKDEP_STILL_OK);
+                __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
+                       NULL);
                 return BUG_TRAP_TYPE_WARN;
         }