linux-kernel - Re: [PATCH v2] panic: add an option to replay all the printk message in buffer

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Message-ID: <20190417105010.GA8492@jagdpanzerIV>
Date:   Wed, 17 Apr 2019 19:50:10 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>, Feng Tang <feng.tang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Borislav Petkov <bp@...e.de>, ying.huang@...el.com,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v2] panic: add an option to replay all the printk message
 in buffer

On (04/17/19 18:46), Sergey Senozhatsky wrote:
> 
> Does not look too complex/ugly.

Looks simpler than adding one more global state to the
console_unlock() printing loop.

// Not tested at all //

---

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 1fd45a8650e1..0fb785ed5ec6 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -179,7 +179,7 @@ extern void panic_flush_kmsg_end(void)
 	kmsg_dump(KMSG_DUMP_PANIC);
 	bust_spinlocks(0);
 	debug_locks_off();
-	console_flush_on_panic();
+	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
 }
 
 static unsigned long oops_begin(struct pt_regs *regs)
diff --git a/include/linux/console.h b/include/linux/console.h
index ec9bdb3d7bab..9e306eb4398a 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -175,7 +175,13 @@ extern int console_trylock(void);
 extern void console_unlock(void);
 extern void console_conditional_schedule(void);
 extern void console_unblank(void);
-extern void console_flush_on_panic(void);
+
+enum console_flush_mode {
+	CONSOLE_FLUSH_PENDING,
+	CONSOLE_FLUSH_ALL,
+};
+
+extern void console_flush_on_panic(enum console_flush_mode flush_mode);
 extern struct tty_driver *console_device(int *);
 extern void console_stop(struct console *);
 extern void console_start(struct console *);
diff --git a/kernel/panic.c b/kernel/panic.c
index cd73af35ec66..50eacfc9bc7e 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -51,6 +51,7 @@ EXPORT_SYMBOL_GPL(panic_timeout);
 #define PANIC_PRINT_TIMER_INFO		0x00000004
 #define PANIC_PRINT_LOCK_INFO		0x00000008
 #define PANIC_PRINT_FTRACE_INFO		0x00000010
+#define PANIC_PRINT_ALL_PRINTK_MSG	0x00000020
 unsigned long panic_print;
 
 ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
@@ -148,6 +149,9 @@ static void panic_print_sys_info(void)
 
 	if (panic_print & PANIC_PRINT_FTRACE_INFO)
 		ftrace_dump(DUMP_ALL);
+
+	if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG)
+		console_flush_on_panic(CONSOLE_FLUSH_ALL);
 }
 
 /**
@@ -277,7 +281,7 @@ void panic(const char *fmt, ...)
 	 * panic() is not being callled from OOPS.
 	 */
 	debug_locks_off();
-	console_flush_on_panic();
+	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
 
 	panic_print_sys_info();
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 17102fd4c136..da60a185dbbb 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2538,7 +2538,7 @@ void console_unblank(void)
  *
  * Immediately output all pending messages no matter what.
  */
-void console_flush_on_panic(void)
+void console_flush_on_panic(enum console_flush_mode flush_mode)
 {
 	/*
 	 * If someone else is holding the console lock, trylock will fail
@@ -2549,6 +2549,14 @@ void console_flush_on_panic(void)
 	 */
 	console_trylock();
 	console_may_schedule = 0;
+	if (flush_mode == CONSOLE_FLUSH_ALL) {
+		/*
+		 * Can be done under logbuf lock, but it's unlikely that
+		 * we will have any race conditions here.
+		 */
+		console_seq = log_first_seq;
+		console_idx = log_first_idx;
+	}
 	console_unlock();
 }
 
---