linux-kernel - [PATCH v2 1/3] powerpc/irq: don't use current_stack_pointer() in check_stack

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Message-Id: <435e0030e942507766cbef5bc95f906262d2ccf2.1579849665.git.christophe.leroy@c-s.fr>
Date:   Fri, 24 Jan 2020 07:07:52 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 1/3] powerpc/irq: don't use current_stack_pointer() in
 check_stack_overflow()

current_stack_pointer() doesn't return the stack pointer, but the
caller's stack frame. See commit bfe9a2cfe91a ("powerpc: Reimplement
__get_SP() as a function not a define") and commit acf620ecf56c
("powerpc: Rename __get_SP() to current_stack_pointer()") for details.

The purpose of check_stack_overflow() is to verify that the stack has
not overflowed.

To really know whether the stack pointer is still within boundaries,
the check must be done directly on the value of r1.

Define a get_sp() macro to get the value of r1 directly. (Adapted from
arch/powerpc/boot/reg.h)

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
v2: Define a get_sp() macro instead of using asm("r1") locally.
---
 arch/powerpc/include/asm/reg.h | 3 +++
 arch/powerpc/kernel/irq.c      | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 1aa46dff0957..d585f2566338 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1450,6 +1450,9 @@ static inline void mtsrin(u32 val, u32 idx)
 
 extern unsigned long current_stack_pointer(void);
 
+register unsigned long __stack_pointer asm("r1");
+#define get_sp()	(__stack_pointer)
+
 extern unsigned long scom970_read(unsigned int address);
 extern void scom970_write(unsigned int address, unsigned long value);
 
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index add67498c126..cd29c2eb2d8e 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -601,7 +601,7 @@ static inline void check_stack_overflow(void)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 	long sp;
 
-	sp = current_stack_pointer() & (THREAD_SIZE-1);
+	sp = get_sp() & (THREAD_SIZE - 1);
 
 	/* check for stack overflow: is there less than 2KB free? */
 	if (unlikely(sp < 2048)) {
-- 
2.25.0