linux-kernel - [PATCH 2/2] arm64: stacktrace: Add skip when task == current

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Date:   Wed, 17 Mar 2021 14:20:50 +0000
From:   Chen Jun <chenjun102@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     <akpm@...ux-foundation.org>, <catalin.marinas@....com>,
        <will@...nel.org>, <rui.xiang@...wei.com>
Subject: [PATCH 2/2] arm64: stacktrace: Add skip when task == current

On ARM64, cat /sys/kernel/debug/page_owner, all pages return the same
stack:
 stack_trace_save+0x4c/0x78
 register_early_stack+0x34/0x70
 init_page_owner+0x34/0x230
 page_ext_init+0x1bc/0x1dc

The reason is that:
check_recursive_alloc always return 1 because that
entries[0] is always equal to ip (__set_page_owner+0x3c/0x60).

The root cause is that:
commit 5fc57df2f6fd ("arm64: stacktrace: Convert to ARCH_STACKWALK")
make the save_trace save 2 more entries.

Add skip in arch_stack_walk when task == current.

Fixes: 5fc57df2f6fd ("arm64: stacktrace: Convert to ARCH_STACKWALK")
Signed-off-by: Chen Jun <chenjun102@...wei.com>
---
 arch/arm64/kernel/stacktrace.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index ad20981..c26b0ac 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -201,11 +201,12 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 
 	if (regs)
 		start_backtrace(&frame, regs->regs[29], regs->pc);
-	else if (task == current)
+	else if (task == current) {
+		((struct stacktrace_cookie *)cookie)->skip += 2;
 		start_backtrace(&frame,
 				(unsigned long)__builtin_frame_address(0),
 				(unsigned long)arch_stack_walk);
-	else
+	} else
 		start_backtrace(&frame, thread_saved_fp(task),
 				thread_saved_pc(task));
 
-- 
2.9.4