[PATCH v11 03/19] dyndbg: add write-to-tracefs code

Jim Cromie
2022-01-07T05:29:59Z

adds: dynamic_trace()
uses trace_console() temporarily to issue printk:console event
uses internal-ish __ftrace_trace_stack code:
4-context buffer stack, barriers per Steve

call it from new funcs:
dynamic_printk() - print to both syslog/tracefs
dynamic_dev_printk() - dev-print to both syslog/tracefs

These handle both _DPRINTK_FLAGS_PRINTK and _DPRINTK_FLAGS_TRACE
cases, allowing to vsnprintf the message once and use it for both,
skipping past the KERN_DEBUG character for tracing.

Finally, adjust the callers: __dynamic_{pr_debug,{,net,ib}dev_dbg},
replacing printk and dev_printk with the new funcs above.

The _DPRINTK_FLAGS_TRACE flag character s 'T', so the following finds
all callsites enabled for tracing:

grep -P =p?T /proc/dynamic_debug/control

Enabling debug-to-tracefs is 2 steps:

# event enable
echo 1 > /sys/kernel/tracing/events/dyndbg/enable
# callsite enable
echo module foo +T > /proc/dynamic_debug/control

This patch,~1,~2 are based upon:
https://lore.kernel.org/lkml/20200825153338.17061-1-vincent.whitchurch@axis.com/

.. with simplification of temporarily reusing trace_console() rather
than adding a new printk:dyndbg event. Soon, add 2 new events
capturing the pr_debug & dev_dbg() args.

CC: vincent.whitchurch@axis.com
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
.../admin-guide/dynamic-debug-howto.rst | 1 +
lib/dynamic_debug.c | 155 +++++++++++++++---
2 files changed, 130 insertions(+), 26 deletions(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index a89cfa083155..3c8f104a143f 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -228,6 +228,7 @@ of the characters::
The flags are::

p enables the pr_debug() callsite.
+ T enables callsite to issue a dyndbg:* trace-event
f Include the function name in the printed message
l Include line number in the printed message
m Include module name in the printed message
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 78a2912976c1..3fd035cd4653 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -36,6 +36,7 @@
#include <linux/sched.h>
#include <linux/device.h>
#include <linux/netdevice.h>
+#include <trace/events/printk.h>

#include <rdma/ib_verbs.h>

@@ -87,6 +88,7 @@ static inline const char *trim_prefix(const char *path)

static struct { unsigned flag:8; char opt_char; } opt_array[] = {
{ _DPRINTK_FLAGS_PRINTK, 'p' },
+ { _DPRINTK_FLAGS_TRACE, 'T' },
{ _DPRINTK_FLAGS_INCL_MODNAME, 'm' },
{ _DPRINTK_FLAGS_INCL_FUNCNAME, 'f' },
{ _DPRINTK_FLAGS_INCL_LINENO, 'l' },
@@ -628,6 +630,96 @@ static inline char *dynamic_emit_prefix(struct _ddebug *desc, char *buf)
return buf;
}

+/*
+ * This code is heavily based on __ftrace_trace_stack().
+ *
+ * Allow 4 levels of nesting: normal, softirq, irq, NMI.
+ */
+#define DYNAMIC_TRACE_NESTING 4
+
+struct dynamic_trace_buf {
+ char buf[256];
+};
+
+struct dynamic_trace_bufs {
+ struct dynamic_trace_buf bufs[DYNAMIC_TRACE_NESTING];
+};
+
+static DEFINE_PER_CPU(struct dynamic_trace_bufs, dynamic_trace_bufs);
+static DEFINE_PER_CPU(int, dynamic_trace_reserve);
+
+static void dynamic_trace(const char *fmt, va_list args)
+{
+ struct dynamic_trace_buf *buf;
+ int bufidx;
+ int len;
+
+ preempt_disable_notrace();
+
+ bufidx = __this_cpu_inc_return(dynamic_trace_reserve) - 1;
+
+ if (WARN_ON_ONCE(bufidx > DYNAMIC_TRACE_NESTING))
+ goto out;
+
+ /* For the same reasons as in __ftrace_trace_stack(). */
+ barrier();
+
+ buf = this_cpu_ptr(dynamic_trace_bufs.bufs) + bufidx;
+
+ len = vscnprintf(buf->buf, sizeof(buf->buf), fmt, args);
+ trace_console(buf->buf, len);
+
+out:
+ /* As above. */
+ barrier();
+ __this_cpu_dec(dynamic_trace_reserve);
+ preempt_enable_notrace();
+}
+
+static void dynamic_printk(unsigned int flags, const char *fmt, ...)
+{
+ if (flags & _DPRINTK_FLAGS_TRACE) {
+ va_list args;
+
+ va_start(args, fmt);
+ /*
+ * All callers include the KERN_DEBUG prefix to keep the
+ * vprintk case simple; strip it out for tracing.
+ */
+ dynamic_trace(fmt + strlen(KERN_DEBUG), args);
+ va_end(args);
+ }
+
+ if (flags & _DPRINTK_FLAGS_PRINTK) {
+ va_list args;
+
+ va_start(args, fmt);
+ vprintk(fmt, args);
+ va_end(args);
+ }
+}
+
+static void dynamic_dev_printk(unsigned int flags, const struct device *dev,
+ const char *fmt, ...)
+{
+
+ if (flags & _DPRINTK_FLAGS_TRACE) {
+ va_list args;
+
+ va_start(args, fmt);
+ dynamic_trace(fmt, args);
+ va_end(args);
+ }
+
+ if (flags & _DPRINTK_FLAGS_PRINTK) {
+ va_list args;
+
+ va_start(args, fmt);
+ dev_vprintk_emit(LOGLEVEL_DEBUG, dev, fmt, args);
+ va_end(args);
+ }
+}
+
void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
{
va_list args;
@@ -642,7 +734,8 @@ void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...)
vaf.fmt = fmt;
vaf.va = &args;

- printk(KERN_DEBUG "%s%pV", dynamic_emit_prefix(descriptor, buf), &vaf);
+ dynamic_printk(descriptor->flags, KERN_DEBUG "%s%pV",
+ dynamic_emit_prefix(descriptor, buf), &vaf);

va_end(args);
}
@@ -652,6 +745,7 @@ void __dynamic_dev_dbg(struct _ddebug *descriptor,
const struct device *dev, const char *fmt, ...)
{
struct va_format vaf;
+ unsigned int flags;
va_list args;

BUG_ON(!descriptor);
@@ -661,16 +755,18 @@ void __dynamic_dev_dbg(struct _ddebug *descriptor,

vaf.fmt = fmt;
vaf.va = &args;
+ flags = descriptor->flags;

if (!dev) {
- printk(KERN_DEBUG "(NULL device *): %pV", &vaf);
+ dynamic_printk(flags, KERN_DEBUG "(NULL device *): %pV",
+ &vaf);
} else {
char buf[PREFIX_SIZE] = "";

- dev_printk_emit(LOGLEVEL_DEBUG, dev, "%s%s %s: %pV",
- dynamic_emit_prefix(descriptor, buf),
- dev_driver_string(dev), dev_name(dev),
- &vaf);
+ dynamic_dev_printk(flags, dev, "%s%s %s: %pV",
+ dynamic_emit_prefix(descriptor, buf),
+ dev_driver_string(dev), dev_name(dev),
+ &vaf);
}

va_end(args);
@@ -683,6 +779,7 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor,
const struct net_device *dev, const char *fmt, ...)
{
struct va_format vaf;
+ unsigned int flags;
va_list args;

BUG_ON(!descriptor);
@@ -692,22 +789,24 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor,

vaf.fmt = fmt;
vaf.va = &args;
+ flags = descriptor->flags;

if (dev && dev->dev.parent) {
char buf[PREFIX_SIZE] = "";

- dev_printk_emit(LOGLEVEL_DEBUG, dev->dev.parent,
- "%s%s %s %s%s: %pV",
- dynamic_emit_prefix(descriptor, buf),
- dev_driver_string(dev->dev.parent),
- dev_name(dev->dev.parent),
- netdev_name(dev), netdev_reg_state(dev),
- &vaf);
+ dynamic_dev_printk(flags, dev->dev.parent,
+ "%s%s %s %s%s: %pV",
+ dynamic_emit_prefix(descriptor, buf),
+ dev_driver_string(dev->dev.parent),
+ dev_name(dev->dev.parent),
+ netdev_name(dev), netdev_reg_state(dev),
+ &vaf);
} else if (dev) {
- printk(KERN_DEBUG "%s%s: %pV", netdev_name(dev),
- netdev_reg_state(dev), &vaf);
+ dynamic_printk(flags, KERN_DEBUG "%s%s: %pV",
+ netdev_name(dev), netdev_reg_state(dev), &vaf);
} else {
- printk(KERN_DEBUG "(NULL net_device): %pV", &vaf);
+ dynamic_printk(flags, KERN_DEBUG "(NULL net_device): %pV",
+ &vaf);
}

va_end(args);
@@ -723,29 +822,33 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
{
struct va_format vaf;
va_list args;
+ unsigned int flags;

va_start(args, fmt);

vaf.fmt = fmt;
vaf.va = &args;
+ flags = descriptor->flags;

if (ibdev && ibdev->dev.parent) {
char buf[PREFIX_SIZE] = "";

- dev_printk_emit(LOGLEVEL_DEBUG, ibdev->dev.parent,
- "%s%s %s %s: %pV",
- dynamic_emit_prefix(descriptor, buf),
- dev_driver_string(ibdev->dev.parent),
- dev_name(ibdev->dev.parent),
- dev_name(&ibdev->dev),
- &vaf);
+ dynamic_dev_printk(flags, ibdev->dev.parent,
+ "%s%s %s %s: %pV",
+ dynamic_emit_prefix(descriptor, buf),
+ dev_driver_string(ibdev->dev.parent),
+ dev_name(ibdev->dev.parent),
+ dev_name(&ibdev->dev),
+ &vaf);
} else if (ibdev) {
- printk(KERN_DEBUG "%s: %pV", dev_name(&ibdev->dev), &vaf);
+ dynamic_printk(flags, KERN_DEBUG "%s%s: %pV",
+ dev_name(&ibdev->dev), &vaf);
} else {
- printk(KERN_DEBUG "(NULL ib_device): %pV", &vaf);
+ dynamic_printk(flags, KERN_DEBUG "(NULL ip_device): %pV",
+ &vaf);
}

- va_end(args);
+va_end(args);
}
EXPORT_SYMBOL(__dynamic_ibdev_dbg);

--
2.33.1