Re: [PATCH] tracing/fgraph: remove unnecessary unlikely()
Sorry for this place, I should consider this situation.
-- Yangtao
On Sun, Nov 4, 2018 at 10:06 PM Steven Rostedt wrote:
>
> On Sat, 3 Nov 2018 22:35:37 -0400
> Yangtao Li wrote:
>
> > WARN_ON() already contains an unlikely(), so it's not necessary to use
> > unlikely.
>
> NACK... see below.
>
> >
> > Signed-off-by: Yangtao Li
> > ---
> > kernel/trace/trace_functions_graph.c | 6 ++
> > 1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/trace/trace_functions_graph.c
> > b/kernel/trace/trace_functions_graph.c
> > index 169b3c44ee97..f8c2a08e4985 100644
> > --- a/kernel/trace/trace_functions_graph.c
> > +++ b/kernel/trace/trace_functions_graph.c
> > @@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace,
> > unsigned long *ret,
> > if (index < 0)
> > index += FTRACE_NOTRACE_DEPTH;
> >
> > - if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
> > + if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
>
> When function graph is enabled, the printk from the warn on will likely
> be traced as well and trigger the same WARN_ON, which will again cause
> a recursion loop and crash and reboot the box with no output at all.
>
> > ftrace_graph_stop();
>
> Notice that I call ftrace_graph_stop() *before* the WARN_ON(). This
> disables the ftrace graph tracer and prevents the recursion loop from
> happening.
>
> There's a reason that the WARN_ON() is placed where it is.
>
> But thanks for the report, it shows that I need to add a comment here
> so that someone else doesn't send a similar patch in the future.
>
> -- Steve
>
>
> > - WARN_ON(1);
> > /* Might as well panic, otherwise we have no where to go */
> > *ret = (unsigned long)panic;
> > return;
> > @@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long
> > frame_pointer)
> >*/
> > ftrace_graph_return();
> >
> > - if (unlikely(!ret)) {
> > + if (WARN_ON(!ret)) {
> > ftrace_graph_stop();
> > - WARN_ON(1);
> > /* Might as well panic. What else to do? */
> > ret = (unsigned long)panic;
> > }
>
Re: [PATCH] tracing/fgraph: remove unnecessary unlikely()
Sorry for this place, I should consider this situation.
-- Yangtao
On Sun, Nov 4, 2018 at 10:06 PM Steven Rostedt wrote:
>
> On Sat, 3 Nov 2018 22:35:37 -0400
> Yangtao Li wrote:
>
> > WARN_ON() already contains an unlikely(), so it's not necessary to use
> > unlikely.
>
> NACK... see below.
>
> >
> > Signed-off-by: Yangtao Li
> > ---
> > kernel/trace/trace_functions_graph.c | 6 ++
> > 1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/trace/trace_functions_graph.c
> > b/kernel/trace/trace_functions_graph.c
> > index 169b3c44ee97..f8c2a08e4985 100644
> > --- a/kernel/trace/trace_functions_graph.c
> > +++ b/kernel/trace/trace_functions_graph.c
> > @@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace,
> > unsigned long *ret,
> > if (index < 0)
> > index += FTRACE_NOTRACE_DEPTH;
> >
> > - if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
> > + if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
>
> When function graph is enabled, the printk from the warn on will likely
> be traced as well and trigger the same WARN_ON, which will again cause
> a recursion loop and crash and reboot the box with no output at all.
>
> > ftrace_graph_stop();
>
> Notice that I call ftrace_graph_stop() *before* the WARN_ON(). This
> disables the ftrace graph tracer and prevents the recursion loop from
> happening.
>
> There's a reason that the WARN_ON() is placed where it is.
>
> But thanks for the report, it shows that I need to add a comment here
> so that someone else doesn't send a similar patch in the future.
>
> -- Steve
>
>
> > - WARN_ON(1);
> > /* Might as well panic, otherwise we have no where to go */
> > *ret = (unsigned long)panic;
> > return;
> > @@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long
> > frame_pointer)
> >*/
> > ftrace_graph_return();
> >
> > - if (unlikely(!ret)) {
> > + if (WARN_ON(!ret)) {
> > ftrace_graph_stop();
> > - WARN_ON(1);
> > /* Might as well panic. What else to do? */
> > ret = (unsigned long)panic;
> > }
>
Re: [PATCH] tracing/fgraph: remove unnecessary unlikely()
On Sat, 3 Nov 2018 22:35:37 -0400
Yangtao Li wrote:
> WARN_ON() already contains an unlikely(), so it's not necessary to use
> unlikely.
NACK... see below.
>
> Signed-off-by: Yangtao Li
> ---
> kernel/trace/trace_functions_graph.c | 6 ++
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/trace/trace_functions_graph.c
> b/kernel/trace/trace_functions_graph.c
> index 169b3c44ee97..f8c2a08e4985 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace,
> unsigned long *ret,
> if (index < 0)
> index += FTRACE_NOTRACE_DEPTH;
>
> - if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
> + if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
When function graph is enabled, the printk from the warn on will likely
be traced as well and trigger the same WARN_ON, which will again cause
a recursion loop and crash and reboot the box with no output at all.
> ftrace_graph_stop();
Notice that I call ftrace_graph_stop() *before* the WARN_ON(). This
disables the ftrace graph tracer and prevents the recursion loop from
happening.
There's a reason that the WARN_ON() is placed where it is.
But thanks for the report, it shows that I need to add a comment here
so that someone else doesn't send a similar patch in the future.
-- Steve
> - WARN_ON(1);
> /* Might as well panic, otherwise we have no where to go */
> *ret = (unsigned long)panic;
> return;
> @@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long
> frame_pointer)
>*/
> ftrace_graph_return();
>
> - if (unlikely(!ret)) {
> + if (WARN_ON(!ret)) {
> ftrace_graph_stop();
> - WARN_ON(1);
> /* Might as well panic. What else to do? */
> ret = (unsigned long)panic;
> }
Re: [PATCH] tracing/fgraph: remove unnecessary unlikely()
On Sat, 3 Nov 2018 22:35:37 -0400
Yangtao Li wrote:
> WARN_ON() already contains an unlikely(), so it's not necessary to use
> unlikely.
NACK... see below.
>
> Signed-off-by: Yangtao Li
> ---
> kernel/trace/trace_functions_graph.c | 6 ++
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/trace/trace_functions_graph.c
> b/kernel/trace/trace_functions_graph.c
> index 169b3c44ee97..f8c2a08e4985 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace,
> unsigned long *ret,
> if (index < 0)
> index += FTRACE_NOTRACE_DEPTH;
>
> - if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
> + if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
When function graph is enabled, the printk from the warn on will likely
be traced as well and trigger the same WARN_ON, which will again cause
a recursion loop and crash and reboot the box with no output at all.
> ftrace_graph_stop();
Notice that I call ftrace_graph_stop() *before* the WARN_ON(). This
disables the ftrace graph tracer and prevents the recursion loop from
happening.
There's a reason that the WARN_ON() is placed where it is.
But thanks for the report, it shows that I need to add a comment here
so that someone else doesn't send a similar patch in the future.
-- Steve
> - WARN_ON(1);
> /* Might as well panic, otherwise we have no where to go */
> *ret = (unsigned long)panic;
> return;
> @@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long
> frame_pointer)
>*/
> ftrace_graph_return();
>
> - if (unlikely(!ret)) {
> + if (WARN_ON(!ret)) {
> ftrace_graph_stop();
> - WARN_ON(1);
> /* Might as well panic. What else to do? */
> ret = (unsigned long)panic;
> }
[PATCH] tracing/fgraph: remove unnecessary unlikely()
WARN_ON() already contains an unlikely(), so it's not necessary to use
unlikely.
Signed-off-by: Yangtao Li
---
kernel/trace/trace_functions_graph.c | 6 ++
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_functions_graph.c
b/kernel/trace/trace_functions_graph.c
index 169b3c44ee97..f8c2a08e4985 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace,
unsigned long *ret,
if (index < 0)
index += FTRACE_NOTRACE_DEPTH;
- if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
+ if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
ftrace_graph_stop();
- WARN_ON(1);
/* Might as well panic, otherwise we have no where to go */
*ret = (unsigned long)panic;
return;
@@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long
frame_pointer)
*/
ftrace_graph_return();
- if (unlikely(!ret)) {
+ if (WARN_ON(!ret)) {
ftrace_graph_stop();
- WARN_ON(1);
/* Might as well panic. What else to do? */
ret = (unsigned long)panic;
}
--
2.17.0
[PATCH] tracing/fgraph: remove unnecessary unlikely()
WARN_ON() already contains an unlikely(), so it's not necessary to use
unlikely.
Signed-off-by: Yangtao Li
---
kernel/trace/trace_functions_graph.c | 6 ++
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_functions_graph.c
b/kernel/trace/trace_functions_graph.c
index 169b3c44ee97..f8c2a08e4985 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace,
unsigned long *ret,
if (index < 0)
index += FTRACE_NOTRACE_DEPTH;
- if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
+ if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
ftrace_graph_stop();
- WARN_ON(1);
/* Might as well panic, otherwise we have no where to go */
*ret = (unsigned long)panic;
return;
@@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long
frame_pointer)
*/
ftrace_graph_return();
- if (unlikely(!ret)) {
+ if (WARN_ON(!ret)) {
ftrace_graph_stop();
- WARN_ON(1);
/* Might as well panic. What else to do? */
ret = (unsigned long)panic;
}
--
2.17.0
