linux-kernel - [patch RFC 08/29] parisc: Put console abuse into one place

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Date:   Sun, 11 Sep 2022 00:27:44 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>
Subject: [patch RFC 08/29] parisc: Put console abuse into one place

PARISC has a hope based mechanism to restore consoles in case of a HPMC
(machine check exception) which is scattered over several places.

Move it into one place to make further changes simpler and add comments.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/parisc/include/asm/pdc.h |    2 +-
 arch/parisc/kernel/pdc_cons.c |   38 +++++++++++++++++++++++++++++++-------
 arch/parisc/kernel/traps.c    |   17 +++++------------
 3 files changed, 37 insertions(+), 20 deletions(-)

--- a/arch/parisc/include/asm/pdc.h
+++ b/arch/parisc/include/asm/pdc.h
@@ -20,7 +20,7 @@ extern unsigned long parisc_pat_pdc_cap;
 #define PDC_TYPE_SNAKE		 2 /* Doesn't support SYSTEM_MAP */
 
 void pdc_console_init(void);	/* in pdc_console.c */
-void pdc_console_restart(void);
+void pdc_console_restart(bool hpmc);
 
 void setup_pdc(void);		/* in inventory.c */
 
--- a/arch/parisc/kernel/pdc_cons.c
+++ b/arch/parisc/kernel/pdc_cons.c
@@ -237,20 +237,44 @@ void __init pdc_console_init(void)
 
 
 /*
- * Used for emergencies. Currently only used if an HPMC occurs. If an
- * HPMC occurs, it is possible that the current console may not be
- * properly initialised after the PDC IO reset. This routine unregisters
- * all of the current consoles, reinitializes the pdc console and
- * registers it.
+ * <Historical comments>
+ *
+ * Used for emergencies.
+ *
+ *  - If an HPMC occurs, it is possible that the current console may not be
+ *    properly initialised after the PDC IO reset. This routine unregisters
+ *    all of the current consoles, reinitializes the pdc console and registers
+ *    it.
+ *
+ *  - Maybe the kernel hasn't booted very far yet and hasn't been able
+ *    to initialize the serial or STI console. In that case we should
+ *    re-enable the pdc console, so that the user will be able to
+ *    identify the problem.
+ *
+ * </Historical comments>
+ *
+ * The above is all wishful thinking:
+ *
+ *  - Invoking [un]register_console() from exception contexts is obviously
+ *    unsafe.
+ *
+ *  - If the HPMC left the machine in unpleasant state and the pdc console
+ *    was already initialized, but later removed due to CON_BOOT then this
+ *    will do nothing.
+ *
+ * Pretend that any of the below works in the same way as we pretend that
+ * any of PARISC works.
  */
-
-void pdc_console_restart(void)
+void pdc_console_restart(bool hpmc)
 {
 	struct console *console;
 
 	if (pdc_console_initialized)
 		return;
 
+	if (!hpmc && console_drivers)
+		return;
+
 	/* If we've already seen the output, don't bother to print it again */
 	if (console_drivers != NULL)
 		pdc_cons.flags &= ~CON_PRINTBUFFER;
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -235,17 +235,12 @@ void die_if_kernel(char *str, struct pt_
 			"                 (__)\\       )\\/\\\n"
 			"                  U  ||----w |\n"
 			"                     ||     ||\n");
-	
+
 	/* unlock the pdc lock if necessary */
 	pdc_emergency_unlock();
 
-	/* maybe the kernel hasn't booted very far yet and hasn't been able 
-	 * to initialize the serial or STI console. In that case we should 
-	 * re-enable the pdc console, so that the user will be able to 
-	 * identify the problem. */
-	if (!console_drivers)
-		pdc_console_restart();
-	
+	pdc_console_restart(false);
+
 	if (err)
 		printk(KERN_CRIT "%s (pid %d): %s (code %ld)\n",
 			current->comm, task_pid_nr(current), str, err);
@@ -429,9 +424,7 @@ void parisc_terminate(char *msg, struct
 	/* unlock the pdc lock if necessary */
 	pdc_emergency_unlock();
 
-	/* restart pdc console if necessary */
-	if (!console_drivers)
-		pdc_console_restart();
+	pdc_console_restart(false);
 
 	/* Not all paths will gutter the processor... */
 	switch(code){
@@ -483,7 +476,7 @@ void notrace handle_interruption(int cod
 	int si_code;
 
 	if (code == 1)
-	    pdc_console_restart();  /* switch back to pdc if HPMC */
+	    pdc_console_restart(true);  /* switch back to pdc if HPMC */
 	else if (!irqs_disabled_flags(regs->gr[0]))
 	    local_irq_enable();