linux-kernel - [PATCH] h8300: Make irq disable and enable a compiler barrier

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Message-ID: <20200918152507.711865ce@gandalf.local.home>
Date:   Fri, 18 Sep 2020 15:25:07 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Yoshinori Sato <ysato@...rs.sourceforge.jp>
Cc:     uclinux-h8-devel@...ts.sourceforge.jp,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Richard Weinberger <richard@...ma-star.at>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH] h8300: Make irq disable and enable a compiler barrier

From: Steven Rostedt (VMware) <rostedt@...dmis.org>

In a conversation on #linux-rt, it was asked if the irq disabling and
enabling functions were a compiler barrier, and reads wont happen outside
these functions from where they were in the call.

I stated that they most definitely need to be, otherwise we would have bugs
all over the place if not. And just to confirm, I looked at the
implementation on x86 which had "memory" as a constraint to the asm, and
that is a compiler barrier. As that was just one arch, I looked at others,
and all the other archs do the same but one. H8300 seems to fail here. And
that is most definitely a bug.

Add the compiler barrier to the enabling and disabling of interrupts on
H8300. As this is a really critical bug, I'm starting to wonder how much
this arch is really used. Let's see how quickly this patch gets added to
the arch, and if it is not applied or responded to within a month, I think
we can safely state that this arch is not maintained.

Reported-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
diff --git a/arch/h8300/include/asm/irqflags.h b/arch/h8300/include/asm/irqflags.h
index 48756b7f405e..477cb9d7785f 100644
--- a/arch/h8300/include/asm/irqflags.h
+++ b/arch/h8300/include/asm/irqflags.h
@@ -15,12 +15,12 @@ static inline h8300flags arch_local_save_flags(void)
 
 static inline void arch_local_irq_disable(void)
 {
-	__asm__ volatile ("orc  #0xc0,ccr");
+	__asm__ volatile ("orc  #0xc0,ccr" : : : "memory");
 }
 
 static inline void arch_local_irq_enable(void)
 {
-	__asm__ volatile ("andc #0x3f,ccr");
+	__asm__ volatile ("andc #0x3f,ccr" : : : "memory");
 }
 
 static inline h8300flags arch_local_irq_save(void)
@@ -28,13 +28,13 @@ static inline h8300flags arch_local_irq_save(void)
 	h8300flags flags;
 
 	__asm__ volatile ("stc ccr,%w0\n\t"
-		      "orc  #0xc0,ccr" : "=r" (flags));
+		      "orc  #0xc0,ccr" : "=r" (flags) : : "memory");
 	return flags;
 }
 
 static inline void arch_local_irq_restore(h8300flags flags)
 {
-	__asm__ volatile ("ldc %w0,ccr" : : "r" (flags) : "cc");
+	__asm__ volatile ("ldc %w0,ccr" : : "r" (flags) : "memory", "cc");
 }
 
 static inline int arch_irqs_disabled_flags(unsigned long flags)
@@ -55,13 +55,13 @@ static inline h8300flags arch_local_save_flags(void)
 
 static inline void arch_local_irq_disable(void)
 {
-	__asm__ volatile ("orc #0x80,ccr\n\t");
+	__asm__ volatile ("orc #0x80,ccr\n\t" : : : "memory");
 }
 
 static inline void arch_local_irq_enable(void)
 {
 	__asm__ volatile ("andc #0x7f,ccr\n\t"
-		      "andc #0xf0,exr\n\t");
+		      "andc #0xf0,exr\n\t" : : : "memory");
 }
 
 static inline h8300flags arch_local_irq_save(void)
@@ -71,7 +71,7 @@ static inline h8300flags arch_local_irq_save(void)
 	__asm__ volatile ("stc ccr,%w0\n\t"
 		      "stc exr,%x0\n\t"
 		      "orc  #0x80,ccr\n\t"
-		      : "=r" (flags));
+		      : "=r" (flags) : : "memory");
 	return flags;
 }
 
@@ -79,7 +79,7 @@ static inline void arch_local_irq_restore(h8300flags flags)
 {
 	__asm__ volatile ("ldc %w0,ccr\n\t"
 		      "ldc %x0,exr"
-		      : : "r" (flags) : "cc");
+		      : : "r" (flags) : "memory", "cc");
 }
 
 static inline int arch_irqs_disabled_flags(h8300flags flags)