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Subject[PATCH 3/6] tracing: Add tp_pstore cmdline to have tracepoints go to pstore
Date
Add the kernel command line tp_pstore option that will have
tracepoints go to persistent ram buffer as well as to the
trace buffer for further debugging. This is similar to tp_printk
cmdline option of ftrace.

Pstore support for event tracing is already added and we enable
logging to pstore only if cmdline is specified.

Passing "tp_pstore" will activate logging to pstore. To turn it
off, the sysctl /proc/sys/kernel/tracepoint_pstore can have '0'
echoed into it. Note, this only works if the cmdline option is
used. Echoing 1 into the sysctl file without the cmdline option
will have no affect.

Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
---
.../admin-guide/kernel-parameters.txt | 21 ++++++++
include/linux/ftrace.h | 6 ++-
kernel/sysctl.c | 7 +++
kernel/trace/Kconfig | 22 +++++++-
kernel/trace/trace.c | 51 +++++++++++++++++++
kernel/trace/trace.h | 7 +++
6 files changed, 112 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9871e649ffef..622cf64d4e5b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4519,6 +4519,27 @@
frequency tracepoints such as irq or sched, can cause
the system to live lock.

+ tp_pstore[FTRACE]
+ Have the tracepoints sent to persistent ram buffer for
+ debugging. This is useful for debugging early boot up
+ and other kernel issues where the system hangs or
+ reboots due to some unclocked access or some buggy
+ driver. Instead of spamming the console with unwanted
+ logs, we can send the logs to pstore buffer for further
+ debugging.
+
+ Last occurred events in the pstore log will be helpful
+ in identifying the reset cause.
+
+ For example, to trace sched event, add to the command
+ line:
+ trace_event=sched tp_pstore
+
+ To turn off having tracepoints sent to pstore,
+ echo 0 > /proc/sys/kernel/tracepoint_pstore
+ Note, echoing 1 into this file without the
+ tracepoint_pstore kernel cmdline option has no effect.
+
traceoff_on_warning
[FTRACE] enable this option to disable tracing when a
warning is hit. This turns off "tracing_on". Tracing can
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index a397907e8d72..7c3074e7ec6b 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -900,6 +900,7 @@ enum ftrace_dump_mode;

extern enum ftrace_dump_mode ftrace_dump_on_oops;
extern int tracepoint_printk;
+extern int tracepoint_pstore;

extern void disable_trace_on_warning(void);
extern int __disable_trace_on_warning;
@@ -907,9 +908,12 @@ extern int __disable_trace_on_warning;
int tracepoint_printk_sysctl(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos);
+int tracepoint_pstore_sysctl(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos);

#else /* CONFIG_TRACING */
-static inline void disable_trace_on_warning(void) { }
+static inline void disable_trace_on_warning(void) { }
#endif /* CONFIG_TRACING */

#ifdef CONFIG_FTRACE_SYSCALLS
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index cc02050fd0c4..3cc1223b8955 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -653,6 +653,13 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = tracepoint_printk_sysctl,
},
+ {
+ .procname = "tracepoint_pstore",
+ .data = &tracepoint_pstore,
+ .maxlen = sizeof(tracepoint_pstore),
+ .mode = 0644,
+ .proc_handler = tracepoint_pstore_sysctl,
+ },
#endif
#ifdef CONFIG_KEXEC_CORE
{
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 5e3de28c7677..d0eed268ee85 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -774,6 +774,27 @@ config TRACING_EVENTS_GPIO
help
Enable tracing events for gpio subsystem

+config TRACING_EVENTS_IO
+ bool "Trace IO read/write events"
+ help
+ Enable tracing events for IO read/write operations.
+ This is useful for debugging random hangs or resets
+ caused due to unclocked access or some buggy driver.
+
+ Output of this trace event can be overwhelming and hence
+ dynamic filtering option based on dynamic debug library
+ is provided to narrow down the issues.
+
+ Eg: Trace all register read/write of mmc subsystem with
+ below command line:
+
+ dyndbg="file drivers/mmc/* +p" trace_event=io
+
+ See Documentation/admin-guide/dynamic-debug-howto.rst for
+ more info on using dynamic debug.
+
+ If unsure, say N.
+
config GCOV_PROFILE_FTRACE
bool "Enable GCOV profiling on ftrace subsystem"
depends on GCOV_KERNEL
@@ -789,4 +810,3 @@ config GCOV_PROFILE_FTRACE
endif # FTRACE

endif # TRACING_SUPPORT
-
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index bf6f1d70484d..018cbbefb769 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -73,6 +73,11 @@ struct trace_iterator *tracepoint_print_iter;
int tracepoint_printk;
static DEFINE_STATIC_KEY_FALSE(tracepoint_printk_key);

+/* Pipe tracepoints to pstore */
+struct trace_iterator *tracepoint_pstore_iter;
+int tracepoint_pstore;
+static DEFINE_STATIC_KEY_FALSE(tracepoint_pstore_key);
+
/* For tracers that don't implement custom flags */
static struct tracer_opt dummy_tracer_opt[] = {
{ }
@@ -238,6 +243,14 @@ static int __init set_tracepoint_printk(char *str)
}
__setup("tp_printk", set_tracepoint_printk);

+static int __init set_tracepoint_pstore(char *str)
+{
+ if ((strcmp(str, "=0") != 0 && strcmp(str, "=off") != 0))
+ tracepoint_pstore = 1;
+ return 1;
+}
+__setup("tp_pstore", set_tracepoint_pstore);
+
unsigned long long ns2usecs(u64 nsec)
{
nsec += 500;
@@ -2376,11 +2389,45 @@ int tracepoint_printk_sysctl(struct ctl_table *table, int write,
return ret;
}

+static DEFINE_MUTEX(tracepoint_pstore_mutex);
+
+int tracepoint_pstore_sysctl(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ int save_tracepoint_pstore;
+ int ret;
+
+ mutex_lock(&tracepoint_pstore_mutex);
+ save_tracepoint_pstore = tracepoint_pstore;
+
+ ret = proc_dointvec(table, write, buffer, lenp, ppos);
+
+ if (!tracepoint_pstore_iter)
+ tracepoint_pstore = 0;
+
+ if (save_tracepoint_pstore == tracepoint_pstore)
+ goto out;
+
+ if (tracepoint_pstore)
+ static_key_enable(&tracepoint_pstore_key.key);
+ else
+ static_key_disable(&tracepoint_pstore_key.key);
+
+ out:
+ mutex_unlock(&tracepoint_pstore_mutex);
+
+ return ret;
+}
+
void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
{
if (static_key_false(&tracepoint_printk_key.key))
output_printk(fbuffer);

+ if (static_key_false(&tracepoint_pstore_key.key))
+ pstore_event_call(fbuffer);
+
event_trigger_unlock_commit(fbuffer->trace_file, fbuffer->buffer,
fbuffer->event, fbuffer->entry,
fbuffer->flags, fbuffer->pc);
@@ -8596,6 +8643,10 @@ void __init early_trace_init(void)
else
static_key_enable(&tracepoint_printk_key.key);
}
+
+ if (tracepoint_pstore)
+ static_key_enable(&tracepoint_pstore_key.key);
+
tracer_alloc_buffers();
}

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 3b8c0e24ab30..edc28d0c27eb 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1843,5 +1843,12 @@ static inline void tracer_hardirqs_off(unsigned long a0, unsigned long a1) { }
#endif

extern struct trace_iterator *tracepoint_print_iter;
+extern struct trace_iterator *tracepoint_pstore_iter;
+
+#ifdef CONFIG_PSTORE_FTRACE
+extern void pstore_event_call(struct trace_event_buffer *fbuffer);
+#else
+static inline void pstore_event_call(struct trace_event_buffer *fbuffer) { }
+#endif

#endif /* _LINUX_KERNEL_TRACE_H */
--
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