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 <rdunlap@xenotime.net>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/kdb.h

@@ -78,6 +78,9 @@ typedef enum {
 	KDB_REASON_SSTEP,	/* Single Step trap. - regs valid */
 } kdb_reason_t;
 
+extern int kdb_trap_printk;
+extern 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 *, ...)

kernel/debug/kdb/kdb_bt.c

@@ -23,6 +23,7 @@ static void kdb_show_stack(struct task_struct *p, void *addr)
 {
 	int old_lvl = console_loglevel;
 	console_loglevel = 15;
+	kdb_trap_printk++;
 	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_struct *p, void *addr)
 		show_stack(p, NULL);
 	}
 	console_loglevel = old_lvl;
+	kdb_trap_printk--;
 }
 
 /*

kernel/debug/kdb/kdb_io.c

@@ -29,6 +29,7 @@
 #define CMD_BUFLEN 256
 char kdb_prompt_str[CMD_BUFLEN];
 
+int kdb_trap_printk;
 
 static void kgdb_transition_check(char *buffer)
 {
@@ -533,12 +534,12 @@ static int kdb_search_string(char *searched, char *searchfor)
 	return 0;
 }
 
-int kdb_printf(const char *fmt, ...)
+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 +550,9 @@ int kdb_printf(const char *fmt, ...)
 	unsigned long uninitialized_var(flags);
 
 	preempt_disable();
+	saved_trap_printk = kdb_trap_printk;
+	kdb_trap_printk = 0;
+
 	/* 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 +579,7 @@ 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 +807,20 @@ int kdb_printf(const char *fmt, ...)
 	} else {
 		__release(kdb_printf_lock);
 	}
+	kdb_trap_printk = saved_trap_printk;
 	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;
+}
+

kernel/debug/kdb/kdb_main.c

@@ -1056,7 +1056,9 @@ static void kdb_dumpregs(struct pt_regs *regs)
 {
 	int old_lvl = console_loglevel;
 	console_loglevel = 15;
+	kdb_trap_printk++;
 	show_regs(regs);
+	kdb_trap_printk--;
 	kdb_printf("\n");
 	console_loglevel = old_lvl;
 }
@@ -1819,7 +1821,9 @@ static int kdb_sr(int argc, const char **argv)
 	if (argc != 1)
 		return KDB_ARGCOUNT;
 	sysrq_toggle_support(1);
+	kdb_trap_printk++;
 	handle_sysrq(*argv[1], NULL);
+	kdb_trap_printk--;
 
 	return 0;
 }

kernel/printk.c

@@ -33,6 +33,7 @@
 #include <linux/bootmem.h>
 #include <linux/syscalls.h>
 #include <linux/kexec.h>
+#include <linux/kdb.h>
 #include <linux/ratelimit.h>
 #include <linux/kmsg_dump.h>
 #include <linux/syslog.h>
@@ -602,6 +603,14 @@ asmlinkage int printk(const char *fmt, ...)
 	va_list args;
 	int r;
 
+#ifdef CONFIG_KGDB_KDB
+	if (unlikely(kdb_trap_printk)) {
+		va_start(args, fmt);
+		r = vkdb_printf(fmt, args);
+		va_end(args);
+		return r;
+	}
+#endif
 	va_start(args, fmt);
 	r = vprintk(fmt, args);
 	va_end(args);