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>

4 files changed, 35 insertions, 4 deletions

diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
index 483fa4e7aaac..2f62fe85f16a 100644
--- 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_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--;
 }
 
 /*
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 58be7e9c9e95..c9b7f4f90bba 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/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 @@ kdb_print_out:
         } 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;
+}
+
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 64ef9ac14ba9..b724c791b6d4 100644
--- 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 *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;
 }
diff --git a/kernel/printk.c b/kernel/printk.c
index 9213b8b5bb4f..444b770c9595 100644
--- a/kernel/printk.c
+++ b/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);