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Message-Id: <bae3e75a0c7f9037e4012ee547842c04cd527931.1575871613.git.christophe.leroy@c-s.fr>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [PATCH 1/2] powerpc/irq: don't use current_stack_pointer() in
 check_stack_overflow()
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Mon,  9 Dec 2019 06:07:21 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/kernel/irq.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index bb34005ff9d2..4d468d835558 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -599,9 +599,8 @@ u64 arch_irq_stat_cpu(unsigned int cpu)
 static inline void check_stack_overflow(void)
 {
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
-	long sp;
-
-	sp = current_stack_pointer() & (THREAD_SIZE-1);
+	register unsigned long r1 asm("r1");
+	long sp = r1 & (THREAD_SIZE - 1);
 
 	/* check for stack overflow: is there less than 2KB free? */
 	if (unlikely(sp < 2048)) {
-- 
2.13.3