[tip:perf/core] perf: Return empty callchain instead of NULL

[tip-bot for Jiri Olsa]

Commit-ID:  99e818cc9a2fa2f483b91b372c47b94b7c98
Gitweb: https://git.kernel.org/tip/99e818cc9a2fa2f483b91b372c47b94b7c98
Author: Jiri Olsa 
AuthorDate: Sun, 7 Jan 2018 17:03:50 +0100
Committer:  Arnaldo Carvalho de Melo 
CommitDate: Mon, 8 Jan 2018 12:35:01 -0300

perf: Return empty callchain instead of NULL

It simplifies the code a bit, because we dump the callchain
Link: http://lkml.kernel.org/n/tip-uqp7qd6aif47g39glnbu9...@git.kernel.org
even if it's empty. With 'empty' callchain we can remove
all the NULL-checking code paths.

Original-patch-from: Peter Zijlstra 
Signed-off-by: Jiri Olsa 
Acked-by: Peter Zijlstra (Intel) 
Cc: Alexander Shishkin 
Cc: Andi Kleen 
Cc: David Ahern 
Cc: Namhyung Kim 
Link: http://lkml.kernel.org/r/20180107160356.28203-7-jo...@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo 
---
 kernel/events/core.c | 30 --
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5fc1ded..4e1a1bf 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5815,19 +5815,11 @@ void perf_output_sample(struct perf_output_handle 
*handle,
perf_output_read(handle, event);
 
if (sample_type & PERF_SAMPLE_CALLCHAIN) {
-   if (data->callchain) {
-   int size = 1;
-
-   if (data->callchain)
-   size += data->callchain->nr;
-
-   size *= sizeof(u64);
+   int size = 1;
 
-   __output_copy(handle, data->callchain, size);
-   } else {
-   u64 nr = 0;
-   perf_output_put(handle, nr);
-   }
+   size += data->callchain->nr;
+   size *= sizeof(u64);
+   __output_copy(handle, data->callchain, size);
}
 
if (sample_type & PERF_SAMPLE_RAW) {
@@ -5980,6 +5972,8 @@ static u64 perf_virt_to_phys(u64 virt)
return phys_addr;
 }
 
+static struct perf_callchain_entry __empty_callchain = { .nr = 0, };
+
 static struct perf_callchain_entry *
 perf_callchain(struct perf_event *event, struct pt_regs *regs)
 {
@@ -5988,12 +5982,14 @@ perf_callchain(struct perf_event *event, struct pt_regs 
*regs)
/* Disallow cross-task user callchains. */
bool crosstask = event->ctx->task && event->ctx->task != current;
const u32 max_stack = event->attr.sample_max_stack;
+   struct perf_callchain_entry *callchain;
 
if (!kernel && !user)
-   return NULL;
+   return &__empty_callchain;
 
-   return get_perf_callchain(regs, 0, kernel, user,
- max_stack, crosstask, true);
+   callchain = get_perf_callchain(regs, 0, kernel, user,
+  max_stack, crosstask, true);
+   return callchain ?: &__empty_callchain;
 }
 
 void perf_prepare_sample(struct perf_event_header *header,
@@ -6018,9 +6014,7 @@ void perf_prepare_sample(struct perf_event_header *header,
int size = 1;
 
data->callchain = perf_callchain(event, regs);
-
-   if (data->callchain)
-   size += data->callchain->nr;
+   size += data->callchain->nr;
 
header->size += size * sizeof(u64);
}

[tip:perf/core] perf: Return empty callchain instead of NULL

[tip-bot for Jiri Olsa]

Commit-ID:  99e818cc9a2fa2f483b91b372c47b94b7c98
Gitweb: https://git.kernel.org/tip/99e818cc9a2fa2f483b91b372c47b94b7c98
Author: Jiri Olsa 
AuthorDate: Sun, 7 Jan 2018 17:03:50 +0100
Committer:  Arnaldo Carvalho de Melo 
CommitDate: Mon, 8 Jan 2018 12:35:01 -0300

perf: Return empty callchain instead of NULL

It simplifies the code a bit, because we dump the callchain
Link: http://lkml.kernel.org/n/tip-uqp7qd6aif47g39glnbu9...@git.kernel.org
even if it's empty. With 'empty' callchain we can remove
all the NULL-checking code paths.

Original-patch-from: Peter Zijlstra 
Signed-off-by: Jiri Olsa 
Acked-by: Peter Zijlstra (Intel) 
Cc: Alexander Shishkin 
Cc: Andi Kleen 
Cc: David Ahern 
Cc: Namhyung Kim 
Link: http://lkml.kernel.org/r/20180107160356.28203-7-jo...@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo 
---
 kernel/events/core.c | 30 --
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5fc1ded..4e1a1bf 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5815,19 +5815,11 @@ void perf_output_sample(struct perf_output_handle 
*handle,
perf_output_read(handle, event);
 
if (sample_type & PERF_SAMPLE_CALLCHAIN) {
-   if (data->callchain) {
-   int size = 1;
-
-   if (data->callchain)
-   size += data->callchain->nr;
-
-   size *= sizeof(u64);
+   int size = 1;
 
-   __output_copy(handle, data->callchain, size);
-   } else {
-   u64 nr = 0;
-   perf_output_put(handle, nr);
-   }
+   size += data->callchain->nr;
+   size *= sizeof(u64);
+   __output_copy(handle, data->callchain, size);
}
 
if (sample_type & PERF_SAMPLE_RAW) {
@@ -5980,6 +5972,8 @@ static u64 perf_virt_to_phys(u64 virt)
return phys_addr;
 }
 
+static struct perf_callchain_entry __empty_callchain = { .nr = 0, };
+
 static struct perf_callchain_entry *
 perf_callchain(struct perf_event *event, struct pt_regs *regs)
 {
@@ -5988,12 +5982,14 @@ perf_callchain(struct perf_event *event, struct pt_regs 
*regs)
/* Disallow cross-task user callchains. */
bool crosstask = event->ctx->task && event->ctx->task != current;
const u32 max_stack = event->attr.sample_max_stack;
+   struct perf_callchain_entry *callchain;
 
if (!kernel && !user)
-   return NULL;
+   return &__empty_callchain;
 
-   return get_perf_callchain(regs, 0, kernel, user,
- max_stack, crosstask, true);
+   callchain = get_perf_callchain(regs, 0, kernel, user,
+  max_stack, crosstask, true);
+   return callchain ?: &__empty_callchain;
 }
 
 void perf_prepare_sample(struct perf_event_header *header,
@@ -6018,9 +6014,7 @@ void perf_prepare_sample(struct perf_event_header *header,
int size = 1;
 
data->callchain = perf_callchain(event, regs);
-
-   if (data->callchain)
-   size += data->callchain->nr;
+   size += data->callchain->nr;
 
header->size += size * sizeof(u64);
}