dump_stack: consolidate dump_stack() implementations and unify their behaviors

Both dump_stack() and show_stack() are currently implemented by each
architecture.  show_stack(NULL, NULL) dumps the backtrace for the
current task as does dump_stack().  On some archs, dump_stack() prints
extra information - pid, utsname and so on - in addition to the
backtrace while the two are identical on other archs.

The usages in arch-independent code of the two functions indicate
show_stack(NULL, NULL) should print out bare backtrace while
dump_stack() is used for debugging purposes when something went wrong,
so it does make sense to print additional information on the task which
triggered dump_stack().

There's no reason to require archs to implement two separate but mostly
identical functions.  It leads to unnecessary subtle information.

This patch expands the dummy fallback dump_stack() implementation in
lib/dump_stack.c such that it prints out debug information (taken from
x86) and invokes show_stack(NULL, NULL) and drops arch-specific
dump_stack() implementations in all archs except blackfin.  Blackfin's
dump_stack() does something wonky that I don't understand.

Debug information can be printed separately by calling
dump_stack_print_info() so that arch-specific dump_stack()
implementation can still emit the same debug information.  This is used
in blackfin.

This patch brings the following behavior changes.

* On some archs, an extra level in backtrace for show_stack() could be
  printed.  This is because the top frame was determined in
  dump_stack() on those archs while generic dump_stack() can't do that
  reliably.  It can be compensated by inlining dump_stack() but not
  sure whether that'd be necessary.

* Most archs didn't use to print debug info on dump_stack().  They do
  now.

An example WARN dump follows.

 WARNING: at kernel/workqueue.c:4841 init_workqueues+0x35/0x505()
 Hardware name: empty
 Modules linked in:
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.9.0-rc1-work+ #9
  0000000000000009 ffff88007c861e08 ffffffff81c614dc ffff88007c861e48
  ffffffff8108f50f ffffffff82228240 0000000000000040 ffffffff8234a03c
  0000000000000000 0000000000000000 0000000000000000 ffff88007c861e58
 Call Trace:
  [<ffffffff81c614dc>] dump_stack+0x19/0x1b
  [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0
  [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20
  [<ffffffff8234a071>] init_workqueues+0x35/0x505
  ...

v2: CPU number added to the generic debug info as requested by s390
    folks and dropped the s390 specific dump_stack().  This loses %ksp
    from the debug message which the maintainers think isn't important
    enough to keep the s390-specific dump_stack() implementation.

    dump_stack_print_info() is moved to kernel/printk.c from
    lib/dump_stack.c.  Because linkage is per objecct file,
    dump_stack_print_info() living in the same lib file as generic
    dump_stack() means that archs which implement custom dump_stack()
    - at this point, only blackfin - can't use dump_stack_print_info()
    as that will bring in the generic version of dump_stack() too.  v1
    The v1 patch broke build on blackfin due to this issue.  The build
    breakage was reported by Fengguang Wu.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Acked-by: Jesper Nilsson <jesper.nilsson@axis.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>	[s390 bits]
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Richard Kuo <rkuo@codeaurora.org>		[hexagon bits]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/kernel/traps.c

@@ -169,13 +169,6 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	dik_show_trace(sp);
 }
 
-void dump_stack(void)
-{
-	show_stack(NULL, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 void
 die_if_kernel(char * str, struct pt_regs *regs, long err, unsigned long *r9_15)
 {

arch/arc/kernel/stacktrace.c

@@ -220,13 +220,6 @@ void show_stack(struct task_struct *tsk, unsigned long *sp)
 	show_stacktrace(tsk, NULL);
 }
 
-/* Expected by Rest of kernel code */
-void dump_stack(void)
-{
-	show_stacktrace(NULL, NULL);
-}
-EXPORT_SYMBOL(dump_stack);
-
 /* Another API expected by schedular, shows up in "ps" as Wait Channel
  * Ofcourse just returning schedule( ) would be pointless so unwind until
  * the function is not in schedular code

arch/arm/kernel/traps.c

@@ -204,13 +204,6 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 }
 #endif
 
-void dump_stack(void)
-{
-	dump_backtrace(NULL, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 void show_stack(struct task_struct *tsk, unsigned long *sp)
 {
 	dump_backtrace(NULL, tsk);

arch/arm64/kernel/traps.c

@@ -167,13 +167,6 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 	}
 }
 
-void dump_stack(void)
-{
-	dump_backtrace(NULL, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 void show_stack(struct task_struct *tsk, unsigned long *sp)
 {
 	dump_backtrace(NULL, tsk);

arch/avr32/kernel/process.c

@@ -204,14 +204,6 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
 	show_stack_log_lvl(tsk, (unsigned long)stack, NULL, "");
 }
 
-void dump_stack(void)
-{
-	unsigned long stack;
-
-	show_trace_log_lvl(current, &stack, NULL, "");
-}
-EXPORT_SYMBOL(dump_stack);
-
 static const char *cpu_modes[] = {
 	"Application", "Supervisor", "Interrupt level 0", "Interrupt level 1",
 	"Interrupt level 2", "Interrupt level 3", "Exception", "NMI"

arch/blackfin/kernel/dumpstack.c

@@ -168,6 +168,7 @@ void dump_stack(void)
 #endif
 	trace_buffer_save(tflags);
 	dump_bfin_trace_buffer();
+	dump_stack_print_info(KERN_DEFAULT);
 	show_stack(current, &stack);
 	trace_buffer_restore(tflags);
 }

arch/c6x/kernel/traps.c

@@ -67,15 +67,6 @@ void show_regs(struct pt_regs *regs)
 	pr_err("A31: %08lx  B31: %08lx\n", regs->a31, regs->b31);
 }
 
-void dump_stack(void)
-{
-	unsigned long stack;
-
-	show_stack(current, &stack);
-}
-EXPORT_SYMBOL(dump_stack);
-
-
 void die(char *str, struct pt_regs *fp, int nr)
 {
 	console_verbose();

arch/cris/kernel/traps.c

@@ -146,13 +146,6 @@ show_stack(void)
 }
 #endif
 
-void
-dump_stack(void)
-{
-	show_stack(NULL, NULL);
-}
-EXPORT_SYMBOL(dump_stack);
-
 void
 set_nmi_handler(void (*handler)(struct pt_regs *))
 {

arch/frv/kernel/traps.c

@@ -466,17 +466,6 @@ asmlinkage void compound_exception(unsigned long esfr1,
 	BUG();
 } /* end compound_exception() */
 
-/*****************************************************************************/
-/*
- * The architecture-independent backtrace generator
- */
-void dump_stack(void)
-{
-	show_stack(NULL, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 void show_stack(struct task_struct *task, unsigned long *sp)
 {
 }

arch/h8300/kernel/traps.c

@@ -164,10 +164,3 @@ void show_trace_task(struct task_struct *tsk)
 {
 	show_stack(tsk,(unsigned long *)tsk->thread.esp0);
 }
-
-void dump_stack(void)
-{
-	show_stack(NULL,NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);

arch/hexagon/kernel/traps.c

@@ -191,14 +191,6 @@ void show_stack(struct task_struct *task, unsigned long *fp)
 	do_show_stack(task, fp, 0);
 }
 
-void dump_stack(void)
-{
-	unsigned long *fp;
-	asm("%0 = r30" : "=r" (fp));
-	show_stack(current, fp);
-}
-EXPORT_SYMBOL(dump_stack);
-
 int die(const char *str, struct pt_regs *regs, long err)
 {
 	static struct {

arch/ia64/kernel/process.c

@@ -95,14 +95,6 @@ show_stack (struct task_struct *task, unsigned long *sp)
 	}
 }
 
-void
-dump_stack (void)
-{
-	show_stack(NULL, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 void
 show_regs (struct pt_regs *regs)
 {

arch/m32r/kernel/traps.c

@@ -167,15 +167,6 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	show_trace(task, sp);
 }
 
-void dump_stack(void)
-{
-	unsigned long stack;
-
-	show_trace(current, &stack);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 static void show_registers(struct pt_regs *regs)
 {
 	int i = 0;

arch/m68k/kernel/traps.c

@@ -991,18 +991,6 @@ void show_stack(struct task_struct *task, unsigned long *stack)
 	show_trace(stack);
 }
 
-/*
- * The architecture-independent backtrace generator
- */
-void dump_stack(void)
-{
-	unsigned long stack;
-
-	show_trace(&stack);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 /*
  * The vector number returned in the frame pointer may also contain
  * the "fs" (Fault Status) bits on ColdFire. These are in the bottom

arch/metag/kernel/traps.c

@@ -987,9 +987,3 @@ void show_stack(struct task_struct *tsk, unsigned long *sp)
 
 	show_trace(tsk, sp, NULL);
 }
-
-void dump_stack(void)
-{
-	show_stack(NULL, NULL);
-}
-EXPORT_SYMBOL(dump_stack);

arch/microblaze/kernel/traps.c

@@ -75,9 +75,3 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 
 	debug_show_held_locks(task);
 }
-
-void dump_stack(void)
-{
-	show_stack(NULL, NULL);
-}
-EXPORT_SYMBOL(dump_stack);

arch/mips/kernel/traps.c

@@ -206,19 +206,6 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	show_stacktrace(task, &regs);
 }
 
-/*
- * The architecture-independent dump_stack generator
- */
-void dump_stack(void)
-{
-	struct pt_regs regs;
-
-	prepare_frametrace(&regs);
-	show_backtrace(current, &regs);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 static void show_code(unsigned int __user *pc)
 {
 	long i;

arch/mn10300/kernel/traps.c

@@ -293,17 +293,6 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	show_trace(sp);
 }
 
-/*
- * the architecture-independent dump_stack generator
- */
-void dump_stack(void)
-{
-	unsigned long stack;
-
-	show_stack(current, &stack);
-}
-EXPORT_SYMBOL(dump_stack);
-
 /*
  * dump the register file in the specified exception frame
  */

arch/openrisc/kernel/traps.c

@@ -105,17 +105,6 @@ void show_trace_task(struct task_struct *tsk)
 	 */
 }
 
-/*
- * The architecture-independent backtrace generator
- */
-void dump_stack(void)
-{
-	unsigned long stack;
-
-	show_stack(current, &stack);
-}
-EXPORT_SYMBOL(dump_stack);
-
 void show_registers(struct pt_regs *regs)
 {
 	int i;

arch/parisc/kernel/traps.c

@@ -158,14 +158,6 @@ void show_regs(struct pt_regs *regs)
 	}
 }
 
-
-void dump_stack(void)
-{
-	show_stack(NULL, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 static void do_show_stack(struct unwind_frame_info *info)
 {
 	int i = 1;

arch/powerpc/kernel/process.c

@@ -1362,12 +1362,6 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
 	} while (count++ < kstack_depth_to_print);
 }
 
-void dump_stack(void)
-{
-	show_stack(current, NULL);
-}
-EXPORT_SYMBOL(dump_stack);
-
 #ifdef CONFIG_PPC64
 /* Called with hard IRQs off */
 void __ppc64_runlatch_on(void)

arch/s390/kernel/dumpstack.c

@@ -129,23 +129,6 @@ static void show_last_breaking_event(struct pt_regs *regs)
 #endif
 }
 
-/*
- * The architecture-independent dump_stack generator
- */
-void dump_stack(void)
-{
-	printk("CPU: %d %s %s %.*s\n",
-	       task_thread_info(current)->cpu, print_tainted(),
-	       init_utsname()->release,
-	       (int)strcspn(init_utsname()->version, " "),
-	       init_utsname()->version);
-	printk("Process %s (pid: %d, task: %p, ksp: %p)\n",
-	       current->comm, current->pid, current,
-	       (void *) current->thread.ksp);
-	show_stack(NULL, NULL);
-}
-EXPORT_SYMBOL(dump_stack);
-
 static inline int mask_bits(struct pt_regs *regs, unsigned long bits)
 {
 	return (regs->psw.mask & bits) / ((~bits + 1) & bits);

arch/score/kernel/traps.c

@@ -149,16 +149,6 @@ static void show_registers(struct pt_regs *regs)
 	printk(KERN_NOTICE "\n");
 }
 
-/*
- * The architecture-independent dump_stack generator
- */
-void dump_stack(void)
-{
-	show_stack(current_thread_info()->task,
-		   (long *) get_irq_regs()->regs[0]);
-}
-EXPORT_SYMBOL(dump_stack);
-
 void __die(const char *str, struct pt_regs *regs, const char *file,
 	const char *func, unsigned long line)
 {

arch/sh/kernel/dumpstack.c

@@ -158,9 +158,3 @@ void show_stack(struct task_struct *tsk, unsigned long *sp)
 		 (unsigned long)task_stack_page(tsk));
 	show_trace(tsk, sp, NULL);
 }
-
-void dump_stack(void)
-{
-	show_stack(NULL, NULL);
-}
-EXPORT_SYMBOL(dump_stack);

arch/sparc/kernel/process_32.c

@@ -164,13 +164,6 @@ void show_stack(struct task_struct *tsk, unsigned long *_ksp)
 	printk("\n");
 }
 
-void dump_stack(void)
-{
-	show_stack(current, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 /*
  * Note: sparc64 has a pretty intricated thread_saved_pc, check it out.
  */

arch/sparc/kernel/traps_64.c

@@ -2350,13 +2350,6 @@ void show_stack(struct task_struct *tsk, unsigned long *_ksp)
 	} while (++count < 16);
 }
 
-void dump_stack(void)
-{
-	show_stack(current, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
 static inline struct reg_window *kernel_stack_up(struct reg_window *rw)
 {
 	unsigned long fp = rw->ins[6];

arch/um/kernel/sysrq.c

@@ -35,18 +35,6 @@ void show_trace(struct task_struct *task, unsigned long * stack)
 }
 #endif
 
-/*
- * stack dumps generator - this is used by arch-independent code.
- * And this is identical to i386 currently.
- */
-void dump_stack(void)
-{
-	unsigned long stack;
-
-	show_trace(current, &stack);
-}
-EXPORT_SYMBOL(dump_stack);
-
 /*Stolen from arch/i386/kernel/traps.c */
 static const int kstack_depth_to_print = 24;
 

arch/unicore32/kernel/traps.c

@@ -170,12 +170,6 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 		c_backtrace(fp, mode);
 }
 
-void dump_stack(void)
-{
-	dump_backtrace(NULL, NULL);
-}
-EXPORT_SYMBOL(dump_stack);
-
 void show_stack(struct task_struct *tsk, unsigned long *sp)
 {
 	dump_backtrace(NULL, tsk);

arch/x86/kernel/dumpstack.c

@@ -191,24 +191,6 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	show_stack_log_lvl(task, NULL, sp, bp, "");
 }
 
-/*
- * The architecture-independent dump_stack generator
- */
-void dump_stack(void)
-{
-	unsigned long bp;
-	unsigned long stack;
-
-	bp = stack_frame(current, NULL);
-	printk("Pid: %d, comm: %.20s %s %s %.*s\n",
-		current->pid, current->comm, print_tainted(),
-		init_utsname()->release,
-		(int)strcspn(init_utsname()->version, " "),
-		init_utsname()->version);
-	show_trace(NULL, NULL, &stack, bp);
-}
-EXPORT_SYMBOL(dump_stack);
-
 static arch_spinlock_t die_lock = __ARCH_SPIN_LOCK_UNLOCKED;
 static int die_owner = -1;
 static unsigned int die_nest_count;

arch/xtensa/kernel/traps.c

@@ -481,14 +481,6 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 	show_trace(task, stack);
 }
 
-void dump_stack(void)
-{
-	show_stack(current, NULL);
-}
-
-EXPORT_SYMBOL(dump_stack);
-
-
 void show_code(unsigned int *pc)
 {
 	long i;

include/linux/printk.h

@@ -145,6 +145,7 @@ extern void wake_up_klogd(void);
 
 void log_buf_kexec_setup(void);
 void __init setup_log_buf(int early);
+void dump_stack_print_info(const char *log_lvl);
 #else
 static inline __printf(1, 0)
 int vprintk(const char *s, va_list args)
@@ -182,6 +183,10 @@ static inline void log_buf_kexec_setup(void)
 static inline void setup_log_buf(int early)
 {
 }
+
+static inline void dump_stack_print_info(const char *log_lvl)
+{
+}
 #endif
 
 extern void dump_stack(void) __cold;

kernel/printk.c

@@ -43,6 +43,7 @@
 #include <linux/rculist.h>
 #include <linux/poll.h>
 #include <linux/irq_work.h>
+#include <linux/utsname.h>
 
 #include <asm/uaccess.h>
 
@@ -2849,4 +2850,21 @@ void kmsg_dump_rewind(struct kmsg_dumper *dumper)
 	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
+
+/**
+ * dump_stack_print_info - print generic debug info for dump_stack()
+ * @log_lvl: log level
+ *
+ * Arch-specific dump_stack() implementations can use this function to
+ * print out the same debug information as the generic dump_stack().
+ */
+void dump_stack_print_info(const char *log_lvl)
+{
+	printk("%sCPU: %d PID: %d Comm: %.20s %s %s %.*s\n",
+	       log_lvl, raw_smp_processor_id(), current->pid, current->comm,
+	       print_tainted(), init_utsname()->release,
+	       (int)strcspn(init_utsname()->version, " "),
+	       init_utsname()->version);
+}
+
 #endif

lib/dump_stack.c

@@ -5,11 +5,16 @@
 
 #include <linux/kernel.h>
 #include <linux/export.h>
+#include <linux/sched.h>
 
+/**
+ * dump_stack - dump the current task information and its stack trace
+ *
+ * Architectures can override this implementation by implementing its own.
+ */
 void dump_stack(void)
 {
-	printk(KERN_NOTICE
-		"This architecture does not implement dump_stack()\n");
+	dump_stack_print_info(KERN_DEFAULT);
+	show_stack(NULL, NULL);
 }
-
 EXPORT_SYMBOL(dump_stack);