[PATCH 0/2] [GIT PULL] tracing: Two fixes for 4.19

[PATCH 0/2] [GIT PULL] tracing: Two fixes for 4.19

[Steven Rostedt]

Linus (aka Greg),

This fixes two bugs:

 - Fix size mismatch of tracepoint array

 - Have preemptirq test module use same clock source of the selftest

Please pull the latest trace-v4.19-rc8 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v4.19-rc8

Tag SHA1: 3a6f9f3dd0418408f594c295e3b8ff6d3528460f
Head SHA1: 12ad0cb2123aed30241a14792ef5bef9efcccbcd


Mathieu Desnoyers (1):
      tracepoint: Fix tracepoint array element size mismatch

Steven Rostedt (VMware) (1):
      tracing: Use trace_clock_local() for looping in preemptirq_delay_test.c

----
 include/linux/module.h               |  3 ++-
 include/linux/tracepoint-defs.h      |  6 ++++++
 include/linux/tracepoint.h           | 36 +++++++++++++++++++++++-------------
 kernel/trace/preemptirq_delay_test.c | 10 +++++-----
 kernel/tracepoint.c                  | 24 ++++++++----------------
 5 files changed, 44 insertions(+), 35 deletions(-)

[PATCH 1/2] tracepoint: Fix tracepoint array element size mismatch

[Steven Rostedt]

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

commit 46e0c9be206f ("kernel: tracepoints: add support for relative
references") changes the layout of the __tracepoint_ptrs section on
architectures supporting relative references. However, it does so
without turning struct tracepoint * const into const int elsewhere in
the tracepoint code, which has the following side-effect:

Setting mod->num_tracepoints is done in by module.c:

    mod->tracepoints_ptrs = section_objs(info, "__tracepoints_ptrs",
                                         sizeof(*mod->tracepoints_ptrs),
                                         &mod->num_tracepoints);

Basically, since sizeof(*mod->tracepoints_ptrs) is a pointer size
(rather than sizeof(int)), num_tracepoints is erroneously set to half the
size it should be on 64-bit arch. So a module with an odd number of
tracepoints misses the last tracepoint due to effect of integer
division.

So in the module going notifier:

        for_each_tracepoint_range(mod->tracepoints_ptrs,
                mod->tracepoints_ptrs + mod->num_tracepoints,
                tp_module_going_check_quiescent, NULL);

the expression (mod->tracepoints_ptrs + mod->num_tracepoints) actually
evaluates to something within the bounds of the array, but miss the
last tracepoint if the number of tracepoints is odd on 64-bit arch.

Fix this by introducing a new typedef: tracepoint_ptr_t, which
is either "const int" on architectures that have PREL32 relocations,
or "struct tracepoint * const" on architectures that does not have
this feature.

Also provide a new tracepoint_ptr_defer() static inline to
encapsulate deferencing this type rather than duplicate code and
ugly idefs within the for_each_tracepoint_range() implementation.

This issue appears in 4.19-rc kernels, and should ideally be fixed
before the end of the rc cycle.

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Jessica Yu <jeyu@kernel.org>
Link: http://lkml.kernel.org/r/20181013191050.22389-1-mathieu.desnoyers@efficios.com
Link: http://lkml.kernel.org/r/20180704083651.24360-7-ard.biesheuvel@linaro.org
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morris <james.morris@microsoft.com>
Cc: James Morris <jmorris@namei.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/module.h          |  3 ++-
 include/linux/tracepoint-defs.h |  6 ++++++
 include/linux/tracepoint.h      | 36 +++++++++++++++++++++------------
 kernel/tracepoint.c             | 24 ++++++++--------------
 4 files changed, 39 insertions(+), 30 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index f807f15bebbe..e19ae08c7fb8 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -20,6 +20,7 @@
 #include <linux/export.h>
 #include <linux/rbtree_latch.h>
 #include <linux/error-injection.h>
+#include <linux/tracepoint-defs.h>
 
 #include <linux/percpu.h>
 #include <asm/module.h>
@@ -430,7 +431,7 @@ struct module {
 
 #ifdef CONFIG_TRACEPOINTS
 	unsigned int num_tracepoints;
-	struct tracepoint * const *tracepoints_ptrs;
+	tracepoint_ptr_t *tracepoints_ptrs;
 #endif
 #ifdef HAVE_JUMP_LABEL
 	struct jump_entry *jump_entries;
diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
index 22c5a46e9693..49ba9cde7e4b 100644
--- a/include/linux/tracepoint-defs.h
+++ b/include/linux/tracepoint-defs.h
@@ -35,6 +35,12 @@ struct tracepoint {
 	struct tracepoint_func __rcu *funcs;
 };
 
+#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
+typedef const int tracepoint_ptr_t;
+#else
+typedef struct tracepoint * const tracepoint_ptr_t;
+#endif
+
 struct bpf_raw_event_map {
 	struct tracepoint	*tp;
 	void			*bpf_func;
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 041f7e56a289..538ba1a58f5b 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -99,6 +99,29 @@ extern void syscall_unregfunc(void);
 #define TRACE_DEFINE_ENUM(x)
 #define TRACE_DEFINE_SIZEOF(x)
 
+#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
+static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
+{
+	return offset_to_ptr(p);
+}
+
+#define __TRACEPOINT_ENTRY(name)					\
+	asm("	.section \"__tracepoints_ptrs\", \"a\"		\n"	\
+	    "	.balign 4					\n"	\
+	    "	.long 	__tracepoint_" #name " - .		\n"	\
+	    "	.previous					\n")
+#else
+static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
+{
+	return *p;
+}
+
+#define __TRACEPOINT_ENTRY(name)					 \
+	static tracepoint_ptr_t __tracepoint_ptr_##name __used		 \
+	__attribute__((section("__tracepoints_ptrs"))) =		 \
+		&__tracepoint_##name
+#endif
+
 #endif /* _LINUX_TRACEPOINT_H */
 
 /*
@@ -253,19 +276,6 @@ extern void syscall_unregfunc(void);
 		return static_key_false(&__tracepoint_##name.key);	\
 	}
 
-#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
-#define __TRACEPOINT_ENTRY(name)					\
-	asm("	.section \"__tracepoints_ptrs\", \"a\"		\n"	\
-	    "	.balign 4					\n"	\
-	    "	.long 	__tracepoint_" #name " - .		\n"	\
-	    "	.previous					\n")
-#else
-#define __TRACEPOINT_ENTRY(name)					 \
-	static struct tracepoint * const __tracepoint_ptr_##name __used	 \
-	__attribute__((section("__tracepoints_ptrs"))) =		 \
-		&__tracepoint_##name
-#endif
-
 /*
  * We have no guarantee that gcc and the linker won't up-align the tracepoint
  * structures, so we create an array of pointers that will be used for iteration
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index bf2c06ef9afc..a3be42304485 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -28,8 +28,8 @@
 #include <linux/sched/task.h>
 #include <linux/static_key.h>
 
-extern struct tracepoint * const __start___tracepoints_ptrs[];
-extern struct tracepoint * const __stop___tracepoints_ptrs[];
+extern tracepoint_ptr_t __start___tracepoints_ptrs[];
+extern tracepoint_ptr_t __stop___tracepoints_ptrs[];
 
 DEFINE_SRCU(tracepoint_srcu);
 EXPORT_SYMBOL_GPL(tracepoint_srcu);
@@ -371,25 +371,17 @@ int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
 }
 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 
-static void for_each_tracepoint_range(struct tracepoint * const *begin,
-		struct tracepoint * const *end,
+static void for_each_tracepoint_range(
+		tracepoint_ptr_t *begin, tracepoint_ptr_t *end,
 		void (*fct)(struct tracepoint *tp, void *priv),
 		void *priv)
 {
+	tracepoint_ptr_t *iter;
+
 	if (!begin)
 		return;
-
-	if (IS_ENABLED(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)) {
-		const int *iter;
-
-		for (iter = (const int *)begin; iter < (const int *)end; iter++)
-			fct(offset_to_ptr(iter), priv);
-	} else {
-		struct tracepoint * const *iter;
-
-		for (iter = begin; iter < end; iter++)
-			fct(*iter, priv);
-	}
+	for (iter = begin; iter < end; iter++)
+		fct(tracepoint_ptr_deref(iter), priv);
 }
 
 #ifdef CONFIG_MODULES
-- 
2.19.0

[PATCH 2/2] tracing: Use trace_clock_local() for looping in preemptirq_delay_test.c

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

The preemptirq_delay_test module is used for the ftrace selftest code that
tests the latency tracers. The problem is that it uses ktime for the delay
loop, and then checks the tracer to see if the delay loop is caught, but the
tracer uses trace_clock_local() which uses various different other clocks to
measure the latency. As ktime uses the clock cycles, and the code then
converts that to nanoseconds, it causes rounding errors, and the preemptirq
latency tests are failing due to being off by 1 (it expects to see a delay
of 500000 us, but the delay is only 499999 us). This is happening due to a
rounding error in the ktime (which is totally legit). The purpose of the
test is to see if it can catch the delay, not to test the accuracy between
trace_clock_local() and ktime_get(). Best to use apples to apples, and have
the delay loop use the same clock as the latency tracer does.

Cc: stable@vger.kernel.org
Fixes: f96e8577da102 ("lib: Add module for testing preemptoff/irqsoff latency tracers")
Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/preemptirq_delay_test.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c
index f704390db9fc..d8765c952fab 100644
--- a/kernel/trace/preemptirq_delay_test.c
+++ b/kernel/trace/preemptirq_delay_test.c
@@ -5,12 +5,12 @@
  * Copyright (C) 2018 Joel Fernandes (Google) <joel@joelfernandes.org>
  */
 
+#include <linux/trace_clock.h>
 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/kernel.h>
 #include <linux/kthread.h>
-#include <linux/ktime.h>
 #include <linux/module.h>
 #include <linux/printk.h>
 #include <linux/string.h>
@@ -25,13 +25,13 @@ MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt or irq (default ir
 
 static void busy_wait(ulong time)
 {
-	ktime_t start, end;
-	start = ktime_get();
+	u64 start, end;
+	start = trace_clock_local();
 	do {
-		end = ktime_get();
+		end = trace_clock_local();
 		if (kthread_should_stop())
 			break;
-	} while (ktime_to_ns(ktime_sub(end, start)) < (time * 1000));
+	} while ((end - start) < (time * 1000));
 }
 
 static int preemptirq_delay_run(void *data)
-- 
2.19.0

Re: [PATCH 0/2] [GIT PULL] tracing: Two fixes for 4.19

[Greg Kroah-Hartman]

On Wed, Oct 17, 2018 at 03:49:39PM -0400, Steven Rostedt wrote:
> 
> Linus (aka Greg),
> 
> This fixes two bugs:
> 
>  - Fix size mismatch of tracepoint array
> 
>  - Have preemptirq test module use same clock source of the selftest

Now pulled, thanks.

greg k-h