linux-kernel - [PATCH] sparc64: Fix irqtrace warnings on Ultra-S

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Message-ID: <20200908154157.GV1362448@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Sep 2020 17:41:57 +0200
From:   peterz@...radead.org
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org, will@...nel.org,
        npiggin@...il.com, elver@...gle.com, jgross@...e.com,
        paulmck@...nel.org, rostedt@...dmis.org, rjw@...ysocki.net,
        joel@...lfernandes.org, svens@...ux.ibm.com, tglx@...utronix.de,
        davem@...emloft.net
Subject: [PATCH] sparc64: Fix irqtrace warnings on Ultra-S

On Tue, Sep 08, 2020 at 07:40:23AM -0700, Guenter Roeck wrote:
> qemu-system-sparc64 -M sun4u -cpu "TI UltraSparc IIi" -m 512 \
>     -initrd rootfs.cpio \
>     -kernel arch/sparc/boot/image -no-reboot \
>     -append "panic=-1 slub_debug=FZPUA rdinit=/sbin/init console=ttyS0" \
>     -nographic -monitor none

Thanks I got it. Also enabling DEBUG_LOCKDEP helps (-:

---
Subject: sparc64: Fix irqtrace warnings on Ultra-S

Recent changes in Lockdep's IRQTRACE broke Ultra-S.

In order avoid redundant IRQ state changes, local_irq_restore() lost the
ability to trace a disable. Change the code to use local_irq_save() to
disable IRQs and then use arch_local_irq_restore() to further disable
NMIs.

This result in slightly suboptimal code, but given this code uses a
global spinlock, performance cannot be its primary purpose.

Fixes: 044d0d6de9f5 ("lockdep: Only trace IRQ edges")
Reported-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
A possible alternative would be:

	local_save_flags(flags);
	arch_local_irq_restore((unsigned long)PIL_NMI);
	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS))
		trace_hardirqs_off();

which generates optimal code, but is more verbose.

 arch/sparc/prom/p1275.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/sparc/prom/p1275.c b/arch/sparc/prom/p1275.c
index 889aa602f8d8..e22233fcf741 100644
--- a/arch/sparc/prom/p1275.c
+++ b/arch/sparc/prom/p1275.c
@@ -37,16 +37,15 @@ void p1275_cmd_direct(unsigned long *args)
 {
 	unsigned long flags;
 
-	local_save_flags(flags);
-	local_irq_restore((unsigned long)PIL_NMI);
+	local_irq_save(flags);
+	arch_local_irq_restore((unsigned long)PIL_NMI);
 	raw_spin_lock(&prom_entry_lock);
 
 	prom_world(1);
 	prom_cif_direct(args);
 	prom_world(0);
 
-	raw_spin_unlock(&prom_entry_lock);
-	local_irq_restore(flags);
+	raw_spin_unlock_irqrestore(&prom_entry_lock, flags);
 }
 
 void prom_cif_init(void *cif_handler, void *cif_stack)