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Subject: [PATCH v3 bpf-next 1/4] perf: expose get/put_callchain_entry()
Date:   Fri, 26 Jun 2020 17:26:05 -0700
Message-ID: <20200627002609.3222870-2-songliubraving@fb.com>
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Sanitize and expose get/put_callchain_entry(). This would be used by bpf
stack map.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 include/linux/perf_event.h |  2 ++
 kernel/events/callchain.c  | 13 ++++++-------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index b4bb32082342c..00ab5efa38334 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1244,6 +1244,8 @@ get_perf_callchain(struct pt_regs *regs, u32 init_n=
r, bool kernel, bool user,
 extern struct perf_callchain_entry *perf_callchain(struct perf_event *ev=
ent, struct pt_regs *regs);
 extern int get_callchain_buffers(int max_stack);
 extern void put_callchain_buffers(void);
+extern struct perf_callchain_entry *get_callchain_entry(int *rctx);
+extern void put_callchain_entry(int rctx);
=20
 extern int sysctl_perf_event_max_stack;
 extern int sysctl_perf_event_max_contexts_per_stack;
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 334d48b16c36d..c6ce894e4ce94 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -149,7 +149,7 @@ void put_callchain_buffers(void)
 	}
 }
=20
-static struct perf_callchain_entry *get_callchain_entry(int *rctx)
+struct perf_callchain_entry *get_callchain_entry(int *rctx)
 {
 	int cpu;
 	struct callchain_cpus_entries *entries;
@@ -159,8 +159,10 @@ static struct perf_callchain_entry *get_callchain_en=
try(int *rctx)
 		return NULL;
=20
 	entries =3D rcu_dereference(callchain_cpus_entries);
-	if (!entries)
+	if (!entries) {
+		put_recursion_context(this_cpu_ptr(callchain_recursion), *rctx);
 		return NULL;
+	}
=20
 	cpu =3D smp_processor_id();
=20
@@ -168,7 +170,7 @@ static struct perf_callchain_entry *get_callchain_ent=
ry(int *rctx)
 		(*rctx * perf_callchain_entry__sizeof()));
 }
=20
-static void
+void
 put_callchain_entry(int rctx)
 {
 	put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
@@ -183,11 +185,8 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr=
, bool kernel, bool user,
 	int rctx;
=20
 	entry =3D get_callchain_entry(&rctx);
-	if (rctx =3D=3D -1)
-		return NULL;
-
 	if (!entry)
-		goto exit_put;
+		return NULL;
=20
 	ctx.entry     =3D entry;
 	ctx.max_stack =3D max_stack;
--=20
2.24.1