[PATCH] lib/bug.c: use common WARN helper

[PATCH] lib/bug.c: use common WARN helper

[Josh Poimboeuf]

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>
---
Based on linux-next/master.

 include/asm-generic/bug.h |  7 +++++++
 kernel/panic.c            | 44 +++++++++++++++++++++++++-------------------
 lib/bug.c                 | 27 +++------------------------
 3 files changed, 35 insertions(+), 43 deletions(-)

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 630dd23..b67a0f9 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -81,6 +81,13 @@ extern void warn_slowpath_null(const char *file, const int line);
 	do { printk(arg); __WARN_TAINT(taint); } while (0)
 #endif
 
+struct warn_args {
+	const char *fmt;
+	va_list 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 d96469d..10f7d94 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 +450,20 @@ void oops_exit(void)
 	kmsg_dump(KMSG_DUMP_OOPS);
 }
 
-#ifdef WANT_WARN_ON_SLOWPATH
-struct slowpath_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 +480,27 @@ 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 +508,18 @@ 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 6cde380..2af139f 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -167,30 +167,9 @@ 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;
 	}
 
-- 
2.4.3

Re: [PATCH] lib/bug.c: use common WARN helper

[Heiko Carstens]

On Mon, Feb 22, 2016 at 09:54:17PM -0600, Josh Poimboeuf wrote:
> 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>
> ---
> Based on linux-next/master.
> 
>  include/asm-generic/bug.h |  7 +++++++
>  kernel/panic.c            | 44 +++++++++++++++++++++++++-------------------
>  lib/bug.c                 | 27 +++------------------------
>  3 files changed, 35 insertions(+), 43 deletions(-)

Nice! Just tested this on s390.

Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>

Re: [PATCH] lib/bug.c: use common WARN helper

[Prarit Bhargava]

On 02/22/2016 10:54 PM, Josh Poimboeuf wrote:
> 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>

<snip>

> -
> -		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);
> +

^^^ minor minor minor nit: extra line here.  Not a big deal but change it if
anyone else complains.

Other than that ...

Acked-and-tested-by: Prarit Bhargava <prarit@redhat.com>

P.

>  		return BUG_TRAP_TYPE_WARN;
>  	}
>  
> 

Re: [PATCH] lib/bug.c: use common WARN helper

[Steven Rostedt]

On Mon, 22 Feb 2016 21:54:17 -0600
Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> 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]()

Note, the "()" were to denote that it's a function. But as it is a "pS"
and not a "ps" which adds the offset, it does make it look funky.

> 
> Reported-by: Chunyu Hu <chuhu@redhat.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> Based on linux-next/master.
> 
>  include/asm-generic/bug.h |  7 +++++++
>  kernel/panic.c            | 44 +++++++++++++++++++++++++-------------------
>  lib/bug.c                 | 27 +++------------------------
>  3 files changed, 35 insertions(+), 43 deletions(-)
> 
> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> index 630dd23..b67a0f9 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -81,6 +81,13 @@ extern void warn_slowpath_null(const char *file, const int line);
>  	do { printk(arg); __WARN_TAINT(taint); } while (0)
>  #endif
>  
> +struct warn_args {
> +	const char *fmt;
> +	va_list args;
> +};

Just a nit. Nothing using warn_args outside of panic.c, thus you don't
need to declare it here. Either add a comment about what these args are
for, or simply do:

/* Used internally by panic */
struct warn_args;


Other than that, the rest looks fine to me.

-- Steve

> +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);				\