generic bug: use show_regs() instead of dump_stack()

The current generic bug implementation has a call to dump_stack() in case a
WARN_ON(whatever) gets hit. Since report_bug(), which calls dump_stack(),
gets called from an exception handler we can do better: just pass the
pt_regs structure to report_bug() and pass it to show_regs() in case of a
warning. This will give more debug informations like register contents,
etc... In addition this avoids some pointless lines that dump_stack()
emits, since it includes a stack backtrace of the exception handler which
is of no interest in case of a warning. E.g. on s390 the following lines
are currently always present in a stack backtrace if dump_stack() gets
called from report_bug():

[<000000000001517a>] show_trace+0x92/0xe8)
[<0000000000015270>] show_stack+0xa0/0xd0
[<00000000000152ce>] dump_stack+0x2e/0x3c
[<0000000000195450>] report_bug+0x98/0xf8
[<0000000000016cc8>] illegal_op+0x1fc/0x21c
[<00000000000227d6>] sysc_return+0x0/0x10

Acked-by: Jeremy Fitzhardinge <[e-mail]>
Acked-by: Haavard Skinnemoen <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Kyle McMartin <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Paul Mundt <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/avr32/kernel/traps.c

···
 	if (!user_mode(regs) && (ecr == ECR_ILLEGAL_OPCODE)) {
 		enum bug_trap_type type;
 
-		type = report_bug(regs->pc);
+		type = report_bug(regs->pc, regs);
 		switch (type) {
 		case BUG_TRAP_TYPE_NONE:
 			break;

arch/i386/kernel/traps.c

···
 		unsigned long esp;
 		unsigned short ss;
 
-		report_bug(regs->eip);
+		report_bug(regs->eip, regs);
 
 		printk(KERN_EMERG "%s: %04lx [#%d]\n", str, err & 0xffff, ++die_counter);
 #ifdef CONFIG_PREEMPT

arch/parisc/kernel/traps.c

···
 	if (unlikely(iir == PARISC_BUG_BREAK_INSN && !user_mode(regs))) {
 		/* check if a BUG() or WARN() trapped here.  */
 		enum bug_trap_type tt;
-		tt = report_bug(regs->iaoq[0] & ~3);
+		tt = report_bug(regs->iaoq[0] & ~3, regs);
 		if (tt == BUG_TRAP_TYPE_WARN) {
 			regs->iaoq[0] += 4;
 			regs->iaoq[1] += 4;

arch/powerpc/kernel/traps.c

···
 			return;
 
 		if (!(regs->msr & MSR_PR) &&  /* not user-mode */
-		    report_bug(regs->nip) == BUG_TRAP_TYPE_WARN) {
+		    report_bug(regs->nip, regs) == BUG_TRAP_TYPE_WARN) {
 			regs->nip += 4;
 			return;
 		}

arch/ppc/kernel/traps.c

···
 			return;
 
 		if (!(regs->msr & MSR_PR) &&  /* not user-mode */
-		    report_bug(regs->nip) == BUG_TRAP_TYPE_WARN) {
+		    report_bug(regs->nip, regs) == BUG_TRAP_TYPE_WARN) {
 			regs->nip += 4;
 			return;
 		}

arch/s390/kernel/traps.c

···
 		else {
 			enum bug_trap_type btt;
 
-			btt = report_bug(regs->psw.addr & PSW_ADDR_INSN);
+			btt = report_bug(regs->psw.addr & PSW_ADDR_INSN, regs);
 			if (btt == BUG_TRAP_TYPE_WARN)
 				return;
 			die(str, regs, interruption_code);

arch/sh/kernel/traps.c

···
 void handle_BUG(struct pt_regs *regs)
 {
 	enum bug_trap_type tt;
-	tt = report_bug(regs->pc);
+	tt = report_bug(regs->pc, regs);
 	if (tt == BUG_TRAP_TYPE_WARN) {
 		regs->pc += 2;
 		return;

arch/x86_64/kernel/traps.c

···
 	unsigned long flags = oops_begin();
 
 	if (!user_mode(regs))
-		report_bug(regs->rip);
+		report_bug(regs->rip, regs);
 
 	__die(str, regs, err);
 	oops_end(flags);

include/linux/bug.h

···
 	BUG_TRAP_TYPE_BUG = 2,
 };
 
+struct pt_regs;
+
 #ifdef CONFIG_GENERIC_BUG
 #include <asm-generic/bug.h>
 
···
 
 const struct bug_entry *find_bug(unsigned long bugaddr);
 
-enum bug_trap_type report_bug(unsigned long bug_addr);
+enum bug_trap_type report_bug(unsigned long bug_addr, struct pt_regs *regs);
 
 int  module_bug_finalize(const Elf_Ehdr *, const Elf_Shdr *,
 			 struct module *);
···
 
 #else	/* !CONFIG_GENERIC_BUG */
 
-static inline enum bug_trap_type report_bug(unsigned long bug_addr)
+static inline enum bug_trap_type report_bug(unsigned long bug_addr,
+					    struct pt_regs *regs)
 {
 	return BUG_TRAP_TYPE_BUG;
 }

lib/bug.c

···
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/bug.h>
+#include <linux/sched.h>
 
 extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
 
···
 	return module_find_bug(bugaddr);
 }
 
-enum bug_trap_type report_bug(unsigned long bugaddr)
+enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 {
 	const struct bug_entry *bug;
 	const char *file;
···
 			       "[verbose debug info unavailable]\n",
 			       (void *)bugaddr);
 
-		dump_stack();
+		show_regs(regs);
 		return BUG_TRAP_TYPE_WARN;
 	}