__WARN() used to just call __WARN_TAINT(TAINT_WARN)
But a call to printk() has been added in the commit identified below
to print a "---- cut here ----" line.
This change only applies to warnings using __WARN(), which means
WARN_ON() where the condition is constant at compile time.
For WARN_ON() with a non constant condition, the additional line is
not printed.
In addition, adding a call to printk() forces GCC to add a stack frame
and save volatile registers. Powerpc has been using traps to implement
warnings in order to avoid that.
So, call __WARN_TAINT(TAINT_WARN) directly instead of using __WARN()
in order to restore the previous behaviour.
If one day powerpc wants the decorative "---- cut here ----" line, it
has to be done in the trap handler, not in the WARN_ON() macro.
Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
Signed-off-by: Christophe Leroy <[email protected]>
---
arch/powerpc/include/asm/bug.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index fed7e6241349..3928fdaebb71 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -99,7 +99,7 @@
int __ret_warn_on = !!(x); \
if (__builtin_constant_p(__ret_warn_on)) { \
if (__ret_warn_on) \
- __WARN(); \
+ __WARN_TAINT(TAINT_WARN); \
} else { \
__asm__ __volatile__( \
"1: "PPC_TLNEI" %4,0\n" \
--
2.13.3
On Mon, Aug 19, 2019 at 01:06:28PM +0000, Christophe Leroy wrote:
> __WARN() used to just call __WARN_TAINT(TAINT_WARN)
>
> But a call to printk() has been added in the commit identified below
> to print a "---- cut here ----" line.
>
> This change only applies to warnings using __WARN(), which means
> WARN_ON() where the condition is constant at compile time.
> For WARN_ON() with a non constant condition, the additional line is
> not printed.
>
> In addition, adding a call to printk() forces GCC to add a stack frame
> and save volatile registers. Powerpc has been using traps to implement
> warnings in order to avoid that.
>
> So, call __WARN_TAINT(TAINT_WARN) directly instead of using __WARN()
> in order to restore the previous behaviour.
>
> If one day powerpc wants the decorative "---- cut here ----" line, it
> has to be done in the trap handler, not in the WARN_ON() macro.
>
> Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
> Signed-off-by: Christophe Leroy <[email protected]>
Ah! Hmpf. Yeah, that wasn't an intended side-effect of this fix.
It seems PPC is not alone in this situation of making this code much
noisier. It looks like there needs to be a way to indicate to the trap
handler that a message was delivered or not. Perhaps we can add another
taint flag?
-kees
> ---
> arch/powerpc/include/asm/bug.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index fed7e6241349..3928fdaebb71 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -99,7 +99,7 @@
> int __ret_warn_on = !!(x); \
> if (__builtin_constant_p(__ret_warn_on)) { \
> if (__ret_warn_on) \
> - __WARN(); \
> + __WARN_TAINT(TAINT_WARN); \
> } else { \
> __asm__ __volatile__( \
> "1: "PPC_TLNEI" %4,0\n" \
> --
> 2.13.3
>
--
Kees Cook
On Mon, Aug 19, 2019 at 09:28:03AM -0700, Kees Cook wrote:
> On Mon, Aug 19, 2019 at 01:06:28PM +0000, Christophe Leroy wrote:
> > __WARN() used to just call __WARN_TAINT(TAINT_WARN)
> >
> > But a call to printk() has been added in the commit identified below
> > to print a "---- cut here ----" line.
> >
> > This change only applies to warnings using __WARN(), which means
> > WARN_ON() where the condition is constant at compile time.
> > For WARN_ON() with a non constant condition, the additional line is
> > not printed.
> >
> > In addition, adding a call to printk() forces GCC to add a stack frame
> > and save volatile registers. Powerpc has been using traps to implement
> > warnings in order to avoid that.
> >
> > So, call __WARN_TAINT(TAINT_WARN) directly instead of using __WARN()
> > in order to restore the previous behaviour.
> >
> > If one day powerpc wants the decorative "---- cut here ----" line, it
> > has to be done in the trap handler, not in the WARN_ON() macro.
> >
> > Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
> > Signed-off-by: Christophe Leroy <[email protected]>
>
> Ah! Hmpf. Yeah, that wasn't an intended side-effect of this fix.
>
> It seems PPC is not alone in this situation of making this code much
> noisier. It looks like there needs to be a way to indicate to the trap
> handler that a message was delivered or not. Perhaps we can add another
> taint flag?
I meant "bug flag" here, not taint. Here's a stab at it. This tries to
remove redundant defines, and moves the "cut here" up into the slow path
explicitly (out of _warn()) and creates a flag so the trap handler can
actually detect if things were already reported...
Thoughts?
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index aa6c093d9ce9..c2b79878f24c 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -10,6 +10,7 @@
#define BUGFLAG_WARNING (1 << 0)
#define BUGFLAG_ONCE (1 << 1)
#define BUGFLAG_DONE (1 << 2)
+#define BUGFLAG_PRINTK (1 << 3)
#define BUGFLAG_TAINT(taint) ((taint) << 8)
#define BUG_GET_TAINT(bug) ((bug)->flags >> 8)
#endif
@@ -62,13 +63,11 @@ struct bug_entry {
#endif
#ifdef __WARN_FLAGS
-#define __WARN_TAINT(taint) __WARN_FLAGS(BUGFLAG_TAINT(taint))
-#define __WARN_ONCE_TAINT(taint) __WARN_FLAGS(BUGFLAG_ONCE|BUGFLAG_TAINT(taint))
-
#define WARN_ON_ONCE(condition) ({ \
int __ret_warn_on = !!(condition); \
if (unlikely(__ret_warn_on)) \
- __WARN_ONCE_TAINT(TAINT_WARN); \
+ __WARN_FLAGS(BUGFLAG_ONCE | \
+ BUGFLAG_TAINT(TAINT_WARN)); \
unlikely(__ret_warn_on); \
})
#endif
@@ -89,7 +88,7 @@ struct bug_entry {
*
* Use the versions with printk format strings to provide better diagnostics.
*/
-#ifndef __WARN_TAINT
+#ifndef __WARN_FLAGS
extern __printf(3, 4)
void warn_slowpath_fmt(const char *file, const int line,
const char *fmt, ...);
@@ -104,12 +103,12 @@ extern void warn_slowpath_null(const char *file, const int line);
warn_slowpath_fmt_taint(__FILE__, __LINE__, taint, arg)
#else
extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
-#define __WARN() do { \
- printk(KERN_WARNING CUT_HERE); __WARN_TAINT(TAINT_WARN); \
-} while (0)
+#define __WARN() __WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN))
#define __WARN_printf(arg...) __WARN_printf_taint(TAINT_WARN, arg)
-#define __WARN_printf_taint(taint, arg...) \
- do { __warn_printk(arg); __WARN_TAINT(taint); } while (0)
+#define __WARN_printf_taint(taint, arg...) do { \
+ __warn_printk(arg); __WARN_FLAGS(BUGFLAG_PRINTK | \
+ BUGFLAG_TAINT(taint)); \
+ } while (0)
#endif
/* used internally by panic.c */
diff --git a/kernel/panic.c b/kernel/panic.c
index 057540b6eee9..03c98da6e3f7 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -551,9 +551,6 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
{
disable_trace_on_warning();
- if (args)
- pr_warn(CUT_HERE);
-
if (file)
pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
raw_smp_processor_id(), current->pid, file, line,
@@ -596,6 +593,7 @@ void warn_slowpath_fmt(const char *file, int line, const char *fmt, ...)
{
struct warn_args args;
+ pr_warn(CUT_HERE);
args.fmt = fmt;
va_start(args.args, fmt);
__warn(file, line, __builtin_return_address(0), TAINT_WARN, NULL,
@@ -609,6 +607,7 @@ void warn_slowpath_fmt_taint(const char *file, int line,
{
struct warn_args args;
+ pr_warn(CUT_HERE);
args.fmt = fmt;
va_start(args.args, fmt);
__warn(file, line, __builtin_return_address(0), taint, NULL, &args);
diff --git a/lib/bug.c b/lib/bug.c
index 1077366f496b..73ce8f9d9eff 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -181,6 +181,10 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
}
}
+ /* Did this trap already report a printk line with "cut here"? */
+ if ((bug->flags & BUGFLAG_PRINTK) == 0)
+ printk(KERN_DEFAULT CUT_HERE);
+
if (warning) {
/* this is a WARN_ON rather than BUG/BUG_ON */
__warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
@@ -188,8 +192,6 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
return BUG_TRAP_TYPE_WARN;
}
- printk(KERN_DEFAULT CUT_HERE);
-
if (file)
pr_crit("kernel BUG at %s:%u!\n", file, line);
else
--
Kees Cook