From: Jason Wessel <jason.wessel@windriver.com>
Subject: [PATCH] printk,kdb: capture printk() when in kdb shell

Certain calls from the kdb shell will call out to printk(), and any of
these calls should get vectored back to the kdb_printf() so that the
kdb pager and processing can be used, as well as to properly channel
I/O to the polled I/O devices.

CC: Randy Dunlap <randy.dunlap@oracle.com>
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

---
 include/linux/kdb.h         |    6 ++++
 kernel/debug/kdb/kdb_bt.c   |    2 +
 kernel/debug/kdb/kdb_io.c   |   56 ++++++++++++++++++++++++++++++++++++++++----
 kernel/debug/kdb/kdb_main.c |    4 +++
 kernel/printk.c             |    8 +++++-
 5 files changed, 71 insertions(+), 5 deletions(-)

--- a/include/linux/kdb.h
+++ b/include/linux/kdb.h
@@ -78,6 +78,12 @@ typedef enum {
 	KDB_REASON_SSTEP,	/* Single Step trap. - regs valid */
 } kdb_reason_t;
 
+/* kdb printk and lowlevel kernel printk interface */
+extern asmlinkage int (*vprintk_func) (const char *, va_list);
+extern void kdb_trap_printk_enable(void);
+extern void kdb_trap_printk_disable(void);
+extern asmlinkage int vkdb_printf(const char *fmt, va_list args)
+	    __attribute__ ((format (printf, 1, 0)));
 extern int kdb_printf(const char *, ...)
 	    __attribute__ ((format (printf, 1, 2)));
 typedef int (*kdb_printf_t)(const char *, ...)
--- a/kernel/debug/kdb/kdb_bt.c
+++ b/kernel/debug/kdb/kdb_bt.c
@@ -23,6 +23,7 @@ static void kdb_show_stack(struct task_s
 {
 	int old_lvl = console_loglevel;
 	console_loglevel = 15;
+	kdb_trap_printk_enable();
 	kdb_set_current_task(p);
 	if (addr) {
 		show_stack((struct task_struct *)p, addr);
@@ -36,6 +37,7 @@ static void kdb_show_stack(struct task_s
 		show_stack(p, NULL);
 	}
 	console_loglevel = old_lvl;
+	kdb_trap_printk_disable();
 }
 
 /*
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -582,6 +582,12 @@ static int have_callable_console(void)
 	return 0;
 }
 
+#ifdef CONFIG_KGDB_KDB
+asmlinkage int (*vprintk_func) (const char *, va_list) = vprintk;
+#else
+#define vprintk_func(x, y) vprintk(x, y)
+#endif
+
 /**
  * printk - print a kernel message
  * @fmt: format string
@@ -610,7 +616,7 @@ asmlinkage int printk(const char *fmt, .
 	int r;
 
 	va_start(args, fmt);
-	r = vprintk(fmt, args);
+	r = vprintk_func(fmt, args);
 	va_end(args);
 
 	return r;
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -29,6 +29,36 @@
 #define CMD_BUFLEN 256
 char kdb_prompt_str[CMD_BUFLEN];
 
+static int kdb_trap_printk;
+
+#ifdef CONFIG_PRINTK
+static inline void kdb_vprintk_func_set(void)
+{
+	vprintk_func = vkdb_printf;
+}
+
+static inline void kdb_vprintk_func_restore(void)
+{
+	vprintk_func = vprintk;
+}
+#else /* ! CONFIG_PRINTK */
+#define kdb_vprintk_func_set()
+#define kdb_vprintk_func_restore()
+#endif /* ! CONFIG_PRINTK */
+
+void kdb_trap_printk_enable(void)
+{
+	if (!kdb_trap_printk)
+		kdb_vprintk_func_set();
+	kdb_trap_printk++;
+}
+
+void kdb_trap_printk_disable(void)
+{
+	kdb_trap_printk--;
+	if (!kdb_trap_printk)
+		kdb_vprintk_func_restore();
+}
 
 static void kgdb_transition_check(char *buffer)
 {
@@ -533,12 +563,12 @@ static int kdb_search_string(char *searc
 	return 0;
 }
 
-int kdb_printf(const char *fmt, ...)
+asmlinkage int vkdb_printf(const char *fmt, va_list ap)
 {
-	va_list ap;
 	int diag;
 	int linecount;
 	int logging, saved_loglevel = 0;
+	int saved_trap_printk;
 	int got_printf_lock = 0;
 	int retlen = 0;
 	int fnd, len;
@@ -549,6 +579,10 @@ int kdb_printf(const char *fmt, ...)
 	unsigned long uninitialized_var(flags);
 
 	preempt_disable();
+	saved_trap_printk = kdb_trap_printk;
+	kdb_trap_printk = 0;
+	kdb_vprintk_func_restore();
+
 	/* Serialize kdb_printf if multiple cpus try to write at once.
 	 * But if any cpu goes recursive in kdb, just print the output,
 	 * even if it is interleaved with any other text.
@@ -575,9 +609,7 @@ int kdb_printf(const char *fmt, ...)
 		next_avail = kdb_buffer;
 		size_avail = sizeof(kdb_buffer);
 	}
-	va_start(ap, fmt);
 	vsnprintf(next_avail, size_avail, fmt, ap);
-	va_end(ap);
 
 	/*
 	 * If kdb_parse() found that the command was cmd xxx | grep yyy
@@ -805,6 +837,22 @@ kdb_print_out:
 	} else {
 		__release(kdb_printf_lock);
 	}
+	kdb_trap_printk = saved_trap_printk;
+	if (kdb_trap_printk > 0)
+		kdb_vprintk_func_set();
 	preempt_enable();
 	return retlen;
 }
+
+int kdb_printf(const char *fmt, ...)
+{
+	va_list ap;
+	int r;
+
+	va_start(ap, fmt);
+	r = vkdb_printf(fmt, ap);
+	va_end(ap);
+
+	return r;
+}
+
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1056,7 +1056,9 @@ static void kdb_dumpregs(struct pt_regs 
 {
 	int old_lvl = console_loglevel;
 	console_loglevel = 15;
+	kdb_trap_printk_enable();
 	show_regs(regs);
+	kdb_trap_printk_disable();
 	kdb_printf("\n");
 	console_loglevel = old_lvl;
 }
@@ -1823,7 +1825,9 @@ static int kdb_sr(int argc, const char *
 		__sysrq_enabled = 1;
 	}
 
+	kdb_trap_printk_enable();
 	handle_sysrq(*argv[1], NULL);
+	kdb_trap_printk_disable();
 
 	return 0;
 }