[for-linus][PATCH 0/7] tracing: More fixes for 5.14

[for-linus][PATCH 0/7] tracing: More fixes for 5.14

[Steven Rostedt]

Fixes and clean ups to tracing:

- Fix warning for use of "main" variable in osnoise tracer

- Fix header alignment when PREEMPT_RT is enabled for osnoise tracer

- Inject "stop" event to see where osnoise stopped the trace

- Define DYNAMIC_FTRACE_WITH_ARGS as some code had an #ifdef for it

- Fix erroneous message for bootconfig cmdline parameter

- Fix crash caused by not found variable in histograms


Daniel Bristot de Oliveira (4):
      trace/osnoise: Rename main variable to tracer_main
      trace/osnoise: Add a header with PREEMPT_RT additional fields
      trace/timerlat: Add a header with PREEMPT_RT additional fields
      trace/osnoise: Print a stop tracing message

Lukas Bulwahn (1):
      tracing: define needed config DYNAMIC_FTRACE_WITH_ARGS

Masami Hiramatsu (1):
      init: Suppress wrong warning for bootconfig cmdline parameter

Steven Rostedt (VMware) (1):
      tracing / histogram: Fix NULL pointer dereference on strcmp() on NULL event name

----
 init/main.c                      |  9 ++++--
 kernel/trace/Kconfig             |  5 ++++
 kernel/trace/trace_events_hist.c |  2 ++
 kernel/trace/trace_osnoise.c     | 62 +++++++++++++++++++++++++++++++++++++---
 4 files changed, 72 insertions(+), 6 deletions(-)

[for-linus][PATCH 1/7] trace/osnoise: Rename main variable to tracer_main

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@kernel.org>

The *main variable in start_kthread() is causing warnings in some
compilers/analyzers. Although it is not necessarily a problem, it is
not a problem changing the variable name too.

Rename the *main variable to *tracer_main.

No functional change.

Link: https://lkml.kernel.org/r/fc62f7deb2258f6068d77c3e734633e3c3511464.1627977494.git.bristot@kernel.org

Cc: Matthew Wilcox <willy@infradead.org>
Fixes: c8895e271f79 ("trace/osnoise: Support hotplug operations")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_osnoise.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index a7e3c24dee13..912036d6a668 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1458,20 +1458,20 @@ static void stop_per_cpu_kthreads(void)
 static int start_kthread(unsigned int cpu)
 {
 	struct task_struct *kthread;
-	void *main = osnoise_main;
+	void *tracer_main = osnoise_main;
 	char comm[24];
 
 #ifdef CONFIG_TIMERLAT_TRACER
 	if (osnoise_data.timerlat_tracer) {
 		snprintf(comm, 24, "timerlat/%d", cpu);
-		main = timerlat_main;
+		tracer_main = timerlat_main;
 	} else {
 		snprintf(comm, 24, "osnoise/%d", cpu);
 	}
 #else
 	snprintf(comm, 24, "osnoise/%d", cpu);
 #endif
-	kthread = kthread_create_on_cpu(main, NULL, cpu, comm);
+	kthread = kthread_create_on_cpu(tracer_main, NULL, cpu, comm);
 
 	if (IS_ERR(kthread)) {
 		pr_err(BANNER "could not start sampling thread\n");
-- 
2.30.2

[for-linus][PATCH 2/7] trace/osnoise: Add a header with PREEMPT_RT additional fields

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@kernel.org>

Some extra flags are printed to the trace header when using the
PREEMPT_RT config. The extra flags are: need-resched-lazy,
preempt-lazy-depth, and migrate-disable.

Without printing these fields, the osnoise specific fields are
shifted by three positions, for example:

 # tracer: osnoise
 #
 #                                _-----=> irqs-off
 #                               / _----=> need-resched
 #                              | / _---=> hardirq/softirq
 #                              || / _--=> preempt-depth                            MAX
 #                              || /                                             SINGLE      Interference counters:
 #                              ||||               RUNTIME      NOISE  %% OF CPU  NOISE    +-----------------------------+
 #           TASK-PID      CPU# ||||   TIMESTAMP    IN US       IN US  AVAILABLE  IN US     HW    NMI    IRQ   SIRQ THREAD
 #              | |         |   ||||      |           |             |    |            |      |      |      |      |      |
            <...>-741     [000] .......  1105.690909: 1000000        234  99.97660      36     21      0   1001     22      3
            <...>-742     [001] .......  1105.691923: 1000000        281  99.97190     197      7      0   1012     35     14
            <...>-743     [002] .......  1105.691958: 1000000       1324  99.86760     118     11      0   1016    155    143
            <...>-744     [003] .......  1105.691998: 1000000        109  99.98910      21      4      0   1004     33      7
            <...>-745     [004] .......  1105.692015: 1000000       2023  99.79770      97     37      0   1023     52     18

Add a new header for osnoise with the missing fields, to be used
when the PREEMPT_RT is enabled.

Link: https://lkml.kernel.org/r/1f03289d2a51fde5a58c2e7def063dc630820ad1.1626598844.git.bristot@kernel.org

Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_osnoise.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 912036d6a668..cbdda2fe4926 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -253,10 +253,40 @@ static struct osnoise_data {
  */
 static bool osnoise_busy;
 
+#ifdef CONFIG_PREEMPT_RT
 /*
  * Print the osnoise header info.
  */
 static void print_osnoise_headers(struct seq_file *s)
+{
+	if (osnoise_data.tainted)
+		seq_puts(s, "# osnoise is tainted!\n");
+
+	seq_puts(s, "#                                _-------=> irqs-off\n");
+	seq_puts(s, "#                               / _------=> need-resched\n");
+	seq_puts(s, "#                              | / _-----=> need-resched-lazy\n");
+	seq_puts(s, "#                              || / _----=> hardirq/softirq\n");
+	seq_puts(s, "#                              ||| / _---=> preempt-depth\n");
+	seq_puts(s, "#                              |||| / _--=> preempt-lazy-depth\n");
+	seq_puts(s, "#                              ||||| / _-=> migrate-disable\n");
+
+	seq_puts(s, "#                              |||||| /          ");
+	seq_puts(s, "                                     MAX\n");
+
+	seq_puts(s, "#                              ||||| /                         ");
+	seq_puts(s, "                    SINGLE      Interference counters:\n");
+
+	seq_puts(s, "#                              |||||||               RUNTIME   ");
+	seq_puts(s, "   NOISE  %% OF CPU  NOISE    +-----------------------------+\n");
+
+	seq_puts(s, "#           TASK-PID      CPU# |||||||   TIMESTAMP    IN US    ");
+	seq_puts(s, "   IN US  AVAILABLE  IN US     HW    NMI    IRQ   SIRQ THREAD\n");
+
+	seq_puts(s, "#              | |         |   |||||||      |           |      ");
+	seq_puts(s, "       |    |            |      |      |      |      |      |\n");
+}
+#else /* CONFIG_PREEMPT_RT */
+static void print_osnoise_headers(struct seq_file *s)
 {
 	if (osnoise_data.tainted)
 		seq_puts(s, "# osnoise is tainted!\n");
@@ -279,6 +309,7 @@ static void print_osnoise_headers(struct seq_file *s)
 	seq_puts(s, "#              | |         |   ||||      |           |      ");
 	seq_puts(s, "       |    |            |      |      |      |      |      |\n");
 }
+#endif /* CONFIG_PREEMPT_RT */
 
 /*
  * osnoise_taint - report an osnoise error.
-- 
2.30.2

[for-linus][PATCH 3/7] trace/timerlat: Add a header with PREEMPT_RT additional fields

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@kernel.org>

Some extra flags are printed to the trace header when using the
PREEMPT_RT config. The extra flags are: need-resched-lazy,
preempt-lazy-depth, and migrate-disable.

Without printing these fields, the timerlat specific fields are
shifted by three positions, for example:

 # tracer: timerlat
 #
 #                                _-----=> irqs-off
 #                               / _----=> need-resched
 #                              | / _---=> hardirq/softirq
 #                              || / _--=> preempt-depth
 #                              || /
 #                              ||||             ACTIVATION
 #           TASK-PID      CPU# ||||   TIMESTAMP    ID            CONTEXT                LATENCY
 #              | |         |   ||||      |         |                  |                       |
           <idle>-0       [000] d..h...  3279.798871: #1     context    irq timer_latency       830 ns
            <...>-807     [000] .......  3279.798881: #1     context thread timer_latency     11301 ns

Add a new header for timerlat with the missing fields, to be used
when the PREEMPT_RT is enabled.

Link: https://lkml.kernel.org/r/babb83529a3211bd0805be0b8c21608230202c55.1626598844.git.bristot@kernel.org

Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_osnoise.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index cbdda2fe4926..f9652278bd10 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -354,6 +354,24 @@ static void trace_osnoise_sample(struct osnoise_sample *sample)
 /*
  * Print the timerlat header info.
  */
+#ifdef CONFIG_PREEMPT_RT
+static void print_timerlat_headers(struct seq_file *s)
+{
+	seq_puts(s, "#                                _-------=> irqs-off\n");
+	seq_puts(s, "#                               / _------=> need-resched\n");
+	seq_puts(s, "#                              | / _-----=> need-resched-lazy\n");
+	seq_puts(s, "#                              || / _----=> hardirq/softirq\n");
+	seq_puts(s, "#                              ||| / _---=> preempt-depth\n");
+	seq_puts(s, "#                              |||| / _--=> preempt-lazy-depth\n");
+	seq_puts(s, "#                              ||||| / _-=> migrate-disable\n");
+	seq_puts(s, "#                              |||||| /\n");
+	seq_puts(s, "#                              |||||||             ACTIVATION\n");
+	seq_puts(s, "#           TASK-PID      CPU# |||||||   TIMESTAMP    ID     ");
+	seq_puts(s, "       CONTEXT                LATENCY\n");
+	seq_puts(s, "#              | |         |   |||||||      |         |      ");
+	seq_puts(s, "            |                       |\n");
+}
+#else /* CONFIG_PREEMPT_RT */
 static void print_timerlat_headers(struct seq_file *s)
 {
 	seq_puts(s, "#                                _-----=> irqs-off\n");
@@ -367,6 +385,7 @@ static void print_timerlat_headers(struct seq_file *s)
 	seq_puts(s, "#              | |         |   ||||      |         |      ");
 	seq_puts(s, "            |                       |\n");
 }
+#endif /* CONFIG_PREEMPT_RT */
 
 /*
  * Record an timerlat_sample into the tracer buffer.
-- 
2.30.2

[for-linus][PATCH 4/7] trace/osnoise: Print a stop tracing message

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@kernel.org>

When using osnoise/timerlat with stop tracing, sometimes it is
not clear in which CPU the stop condition was hit, mainly
when using some extra events.

Print a message informing in which CPU the trace stopped, like
in the example below:

          <idle>-0       [006] d.h.  2932.676616: #1672599 context    irq timer_latency     34689 ns
          <idle>-0       [006] dNh.  2932.676618: irq_noise: local_timer:236 start 2932.676615639 duration 2391 ns
          <idle>-0       [006] dNh.  2932.676620: irq_noise: virtio0-output.0:47 start 2932.676620180 duration 86 ns
          <idle>-0       [003] d.h.  2932.676621: #1673374 context    irq timer_latency      1200 ns
          <idle>-0       [006] d...  2932.676623: thread_noise: swapper/6:0 start 2932.676615964 duration 4339 ns
          <idle>-0       [003] dNh.  2932.676623: irq_noise: local_timer:236 start 2932.676620597 duration 1881 ns
          <idle>-0       [006] d...  2932.676623: sched_switch: prev_comm=swapper/6 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=timerlat/6 next_pid=852 next_prio=4
      timerlat/6-852     [006] ....  2932.676623: #1672599 context thread timer_latency     41931 ns
          <idle>-0       [003] d...  2932.676623: thread_noise: swapper/3:0 start 2932.676620854 duration 880 ns
          <idle>-0       [003] d...  2932.676624: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=timerlat/3 next_pid=849 next_prio=4
      timerlat/6-852     [006] ....  2932.676624: timerlat_main: stop tracing hit on cpu 6
      timerlat/3-849     [003] ....  2932.676624: #1673374 context thread timer_latency      4310 ns

Link: https://lkml.kernel.org/r/b30a0d7542adba019185f44ee648e60e14923b11.1626598844.git.bristot@kernel.org

Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_osnoise.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index f9652278bd10..b576e96d9741 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1075,9 +1075,13 @@ diff_osn_sample_stats(struct osnoise_variables *osn_var, struct osnoise_sample *
 /*
  * osnoise_stop_tracing - Stop tracing and the tracer.
  */
-static void osnoise_stop_tracing(void)
+static __always_inline void osnoise_stop_tracing(void)
 {
 	struct trace_array *tr = osnoise_trace;
+
+	trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_,
+			"stop tracing hit on cpu %d\n", smp_processor_id());
+
 	tracer_tracing_off(tr);
 }
 
-- 
2.30.2

[for-linus][PATCH 5/7] tracing: define needed config DYNAMIC_FTRACE_WITH_ARGS

[Steven Rostedt]

From: Lukas Bulwahn <lukas.bulwahn@gmail.com>

Commit 2860cd8a2353 ("livepatch: Use the default ftrace_ops instead of
REGS when ARGS is available") intends to enable config LIVEPATCH when
ftrace with ARGS is available. However, the chain of configs to enable
LIVEPATCH is incomplete, as HAVE_DYNAMIC_FTRACE_WITH_ARGS is available,
but the definition of DYNAMIC_FTRACE_WITH_ARGS, combining DYNAMIC_FTRACE
and HAVE_DYNAMIC_FTRACE_WITH_ARGS, needed to enable LIVEPATCH, is missing
in the commit.

Fortunately, ./scripts/checkkconfigsymbols.py detects this and warns:

DYNAMIC_FTRACE_WITH_ARGS
Referencing files: kernel/livepatch/Kconfig

So, define the config DYNAMIC_FTRACE_WITH_ARGS analogously to the already
existing similar configs, DYNAMIC_FTRACE_WITH_REGS and
DYNAMIC_FTRACE_WITH_DIRECT_CALLS, in ./kernel/trace/Kconfig to connect the
chain of configs.

Link: https://lore.kernel.org/kernel-janitors/CAKXUXMwT2zS9fgyQHKUUiqo8ynZBdx2UEUu1WnV_q0OCmknqhw@mail.gmail.com/
Link: https://lkml.kernel.org/r/20210806195027.16808-1-lukas.bulwahn@gmail.com

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: stable@vger.kernel.org
Fixes: 2860cd8a2353 ("livepatch: Use the default ftrace_ops instead of REGS when ARGS is available")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/Kconfig | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index d567b1717c4c..3ee23f4d437f 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -219,6 +219,11 @@ config DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	depends on DYNAMIC_FTRACE_WITH_REGS
 	depends on HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 
+config DYNAMIC_FTRACE_WITH_ARGS
+	def_bool y
+	depends on DYNAMIC_FTRACE
+	depends on HAVE_DYNAMIC_FTRACE_WITH_ARGS
+
 config FUNCTION_PROFILER
 	bool "Kernel function profiler"
 	depends on FUNCTION_TRACER
-- 
2.30.2

[for-linus][PATCH 6/7] init: Suppress wrong warning for bootconfig cmdline parameter

[Steven Rostedt]

From: Masami Hiramatsu <mhiramat@kernel.org>

Since the 'bootconfig' command line parameter is handled before
parsing the command line, it doesn't use early_param(). But in
this case, kernel shows a wrong warning message about it.

[    0.013714] Kernel command line: ro console=ttyS0  bootconfig console=tty0
[    0.013741] Unknown command line parameters: bootconfig

To suppress this message, add a dummy handler for 'bootconfig'.

Link: https://lkml.kernel.org/r/162812945097.77369.1849780946468010448.stgit@devnote2

Fixes: 86d1919a4fb0 ("init: print out unknown kernel parameters")
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 init/main.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/init/main.c b/init/main.c
index f5b8246e8aa1..8d97aba78c3a 100644
--- a/init/main.c
+++ b/init/main.c
@@ -397,6 +397,12 @@ static int __init bootconfig_params(char *param, char *val,
 	return 0;
 }
 
+static int __init warn_bootconfig(char *str)
+{
+	/* The 'bootconfig' has been handled by bootconfig_params(). */
+	return 0;
+}
+
 static void __init setup_boot_config(void)
 {
 	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
@@ -475,9 +481,8 @@ static int __init warn_bootconfig(char *str)
 	pr_warn("WARNING: 'bootconfig' found on the kernel command line but CONFIG_BOOT_CONFIG is not set.\n");
 	return 0;
 }
-early_param("bootconfig", warn_bootconfig);
-
 #endif
+early_param("bootconfig", warn_bootconfig);
 
 /* Change NUL term back to "=", to make "param" the whole string. */
 static void __init repair_env_string(char *param, char *val)
-- 
2.30.2

[for-linus][PATCH 7/7] tracing / histogram: Fix NULL pointer dereference on strcmp() on NULL event name

[Steven Rostedt]

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

The following commands:

 # echo 'read_max u64 size;' > synthetic_events
 # echo 'hist:keys=common_pid:count=count:onmax($count).trace(read_max,count)' > events/syscalls/sys_enter_read/trigger

Causes:

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] PREEMPT SMP
 CPU: 4 PID: 1763 Comm: bash Not tainted 5.14.0-rc2-test+ #155
 Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01
v03.03 07/14/2016
 RIP: 0010:strcmp+0xc/0x20
 Code: 75 f7 31 c0 0f b6 0c 06 88 0c 02 48 83 c0 01 84 c9 75 f1 4c 89 c0
c3 0f 1f 80 00 00 00 00 31 c0 eb 08 48 83 c0 01 84 d2 74 0f <0f> b6 14 07
3a 14 06 74 ef 19 c0 83 c8 01 c3 31 c0 c3 66 90 48 89
 RSP: 0018:ffffb5fdc0963ca8 EFLAGS: 00010246
 RAX: 0000000000000000 RBX: ffffffffb3a4e040 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: ffff9714c0d0b640 RDI: 0000000000000000
 RBP: 0000000000000000 R08: 00000022986b7cde R09: ffffffffb3a4dff8
 R10: 0000000000000000 R11: 0000000000000000 R12: ffff9714c50603c8
 R13: 0000000000000000 R14: ffff97143fdf9e48 R15: ffff9714c01a2210
 FS:  00007f1fa6785740(0000) GS:ffff9714da400000(0000)
knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000000 CR3: 000000002d863004 CR4: 00000000001706e0
 Call Trace:
  __find_event_file+0x4e/0x80
  action_create+0x6b7/0xeb0
  ? kstrdup+0x44/0x60
  event_hist_trigger_func+0x1a07/0x2130
  trigger_process_regex+0xbd/0x110
  event_trigger_write+0x71/0xd0
  vfs_write+0xe9/0x310
  ksys_write+0x68/0xe0
  do_syscall_64+0x3b/0x90
  entry_SYSCALL_64_after_hwframe+0x44/0xae
 RIP: 0033:0x7f1fa6879e87

The problem was the "trace(read_max,count)" where the "count" should be
"$count" as "onmax()" only handles variables (although it really should be
able to figure out that "count" is a field of sys_enter_read). But there's
a path that does not find the variable and ends up passing a NULL for the
event, which ends up getting passed to "strcmp()".

Add a check for NULL to return and error on the command with:

 # cat error_log
  hist:syscalls:sys_enter_read: error: Couldn't create or find variable
  Command: hist:keys=common_pid:count=count:onmax($count).trace(read_max,count)
                                ^
Link: https://lkml.kernel.org/r/20210808003011.4037f8d0@oasis.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 50450603ec9cb tracing: Add 'onmax' hist trigger action support
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_events_hist.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 949ef09dc537..a48aa2a2875b 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -3430,6 +3430,8 @@ trace_action_create_field_var(struct hist_trigger_data *hist_data,
 			event = data->match_data.event;
 		}
 
+		if (!event)
+			goto free;
 		/*
 		 * At this point, we're looking at a field on another
 		 * event.  Because we can't modify a hist trigger on
-- 
2.30.2