Re: [PATCH v10 08/10] dyndbg: add print-to-tracefs, selftest with it - RFC

[Vincent Whitchurch <vincent.whitchurch@axis.com>]

On Wed, Dec 08, 2021 at 06:16:10AM +0100, jim.cromie@gmail.com wrote:
> are you planning to dust this patchset off and resubmit it ?
> 
> Ive been playing with it and learning ftrace (decade+ late),
> I found your boot-line example very helpful as 1st steps
> (still havent even tried the filtering)
> 
> 
> with these adjustments (voiced partly to test my understanding)
> I would support it, and rework my patchset to use it.
> 
> - change flag to -e, good mnemonics for event/trace-event
>    T is good too, but uppercase, no need to go there.

Any flag name works for me.

> - include/trace/events/dyndbg.h - separate file, not mixed with print.h
>   dyndbg class, so trace_event=dyndbg:*
> 
> - 1 event type per pr_debug, dev_dbg, netdev_dbg ? ibdev_dbg ?
>   with the extra args: descriptor that Steven wanted,
>   probably also struct <|net|ib>dev

For my use cases I don't see much value in having separate events for
the different debug functions, but since all of them can be easily
enabled (dyndbg:*, as you noted), that works for me too.

> If youre too busy for a while, I'd eventually take a (slow) run at it.

You're welcome to have a go.  I think you've already rebased the
patchset, but here's a diff top of v5.16-rc4 for reference.  I noticed a
bug inside the CONFIG_JUMP_LABEL handling (also present in the last
version I posted) which should be fixed as part of the diff below (I've
added a comment).  Proper tests for this, like the ones you are adding
in your patchset, would certainly be a good idea.  Thanks.

8<-------------
diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index a89cfa083155..b9c4e808befc 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.
+  x    enables trace to the printk:dyndbg 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/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index dce631e678dd..bc21bfb0fdc6 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -27,7 +27,7 @@ struct _ddebug {
 	 * writes commands to <debugfs>/dynamic_debug/control
 	 */
 #define _DPRINTK_FLAGS_NONE	0
-#define _DPRINTK_FLAGS_PRINT	(1<<0) /* printk() a message using the format */
+#define _DPRINTK_FLAGS_PRINTK	(1<<0) /* printk() a message using the format */
 #define _DPRINTK_FLAGS_INCL_MODNAME	(1<<1)
 #define _DPRINTK_FLAGS_INCL_FUNCNAME	(1<<2)
 #define _DPRINTK_FLAGS_INCL_LINENO	(1<<3)
@@ -37,8 +37,11 @@ struct _ddebug {
 	(_DPRINTK_FLAGS_INCL_MODNAME | _DPRINTK_FLAGS_INCL_FUNCNAME |\
 	 _DPRINTK_FLAGS_INCL_LINENO  | _DPRINTK_FLAGS_INCL_TID)
 
+#define _DPRINTK_FLAGS_TRACE		(1<<5)
+#define _DPRINTK_FLAGS_ENABLE		(_DPRINTK_FLAGS_PRINTK | \
+					 _DPRINTK_FLAGS_TRACE)
 #if defined DEBUG
-#define _DPRINTK_FLAGS_DEFAULT _DPRINTK_FLAGS_PRINT
+#define _DPRINTK_FLAGS_DEFAULT _DPRINTK_FLAGS_PRINTK
 #else
 #define _DPRINTK_FLAGS_DEFAULT 0
 #endif
@@ -120,10 +123,10 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 
 #ifdef DEBUG
 #define DYNAMIC_DEBUG_BRANCH(descriptor) \
-	likely(descriptor.flags & _DPRINTK_FLAGS_PRINT)
+	likely(descriptor.flags & _DPRINTK_FLAGS_ENABLE)
 #else
 #define DYNAMIC_DEBUG_BRANCH(descriptor) \
-	unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)
+	unlikely(descriptor.flags & _DPRINTK_FLAGS_ENABLE)
 #endif
 
 #endif /* CONFIG_JUMP_LABEL */
diff --git a/include/trace/events/printk.h b/include/trace/events/printk.h
index 13d405b2fd8b..1f78bd237a91 100644
--- a/include/trace/events/printk.h
+++ b/include/trace/events/printk.h
@@ -7,7 +7,7 @@
 
 #include <linux/tracepoint.h>
 
-TRACE_EVENT(console,
+DECLARE_EVENT_CLASS(printk,
 	TP_PROTO(const char *text, size_t len),
 
 	TP_ARGS(text, len),
@@ -31,6 +31,16 @@ TRACE_EVENT(console,
 
 	TP_printk("%s", __get_str(msg))
 );
+
+DEFINE_EVENT(printk, console,
+	TP_PROTO(const char *text, size_t len),
+	TP_ARGS(text, len)
+);
+
+DEFINE_EVENT(printk, dyndbg,
+	TP_PROTO(const char *text, size_t len),
+	TP_ARGS(text, len)
+);
 #endif /* _TRACE_PRINTK_H */
 
 /* This part must be outside protection */
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index dd7f56af9aed..161454fa0af8 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>
 
@@ -86,11 +87,12 @@ static inline const char *trim_prefix(const char *path)
 }
 
 static struct { unsigned flag:8; char opt_char; } opt_array[] = {
-	{ _DPRINTK_FLAGS_PRINT, 'p' },
+	{ _DPRINTK_FLAGS_PRINTK, 'p' },
 	{ _DPRINTK_FLAGS_INCL_MODNAME, 'm' },
 	{ _DPRINTK_FLAGS_INCL_FUNCNAME, 'f' },
 	{ _DPRINTK_FLAGS_INCL_LINENO, 'l' },
 	{ _DPRINTK_FLAGS_INCL_TID, 't' },
+	{ _DPRINTK_FLAGS_TRACE, 'x' },
 	{ _DPRINTK_FLAGS_NONE, '_' },
 };
 
@@ -210,11 +212,23 @@ static int ddebug_change(const struct ddebug_query *query,
 			if (newflags == dp->flags)
 				continue;
 #ifdef CONFIG_JUMP_LABEL
-			if (dp->flags & _DPRINTK_FLAGS_PRINT) {
-				if (!(modifiers->flags & _DPRINTK_FLAGS_PRINT))
+			if (dp->flags & _DPRINTK_FLAGS_ENABLE) {
+				/*
+				 * The newflags check is to ensure that the
+				 * static branch doesn't get disabled in step
+				 * 3:
+				 *
+				 * (1) +pf
+				 * (2) +x
+				 * (3) -pf
+				 */
+				if (!(modifiers->flags & _DPRINTK_FLAGS_ENABLE) &&
+				    !(newflags & _DPRINTK_FLAGS_ENABLE)) {
 					static_branch_disable(&dp->key.dd_key_true);
-			} else if (modifiers->flags & _DPRINTK_FLAGS_PRINT)
+				}
+			} else if (modifiers->flags & _DPRINTK_FLAGS_ENABLE) {
 				static_branch_enable(&dp->key.dd_key_true);
+			}
 #endif
 			dp->flags = newflags;
 			v4pr_info("changed %s:%d [%s]%s =%s\n",
@@ -621,6 +635,96 @@ static char *__dynamic_emit_prefix(const 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_dyndbg(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);
+	}
+}
+
 static inline char *dynamic_emit_prefix(struct _ddebug *desc, char *buf)
 {
 	if (unlikely(desc->flags & _DPRINTK_FLAGS_INCL_ANY))
@@ -642,7 +746,8 @@ 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 +757,7 @@ 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 +767,18 @@ 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 +791,7 @@ 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 +801,24 @@ 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);
@@ -722,27 +833,31 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 			 const struct ib_device *ibdev, const char *fmt, ...)
 {
 	struct va_format vaf;
+	unsigned int flags;
 	va_list args;
 
 	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: %pV",
+			       dev_name(&ibdev->dev), &vaf);
 	} else {
-		printk(KERN_DEBUG "(NULL ib_device): %pV", &vaf);
+		dynamic_printk(flags, KERN_DEBUG "(NULL ib_device): %pV",
+			       &vaf);
 	}
 
 	va_end(args);