Re: [PATCH 2/2] arm64: stacktrace: Add skip when task == current
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-03-17 18:37:49
Also in:
lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
On Wed, Mar 17, 2021 at 02:20:50PM +0000, Chen Jun wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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));
I don't like abusing the cookie here. It's void * as it's meant to be an opaque type. I'd rather skip the first two frames in walk_stackframe() instead before invoking fn(). Prior to the conversion to ARCH_STACKWALK, we were indeed skipping two more entries in __save_stack_trace() if tsk == current. Something like below, completely untested:
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index ad20981dfda4..2a9f759aa41a 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c@@ -115,10 +115,15 @@ NOKPROBE_SYMBOL(unwind_frame); void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame, bool (*fn)(void *, unsigned long), void *data) { + /* for the current task, we don't want this function nor its caller */ + int skip = tsk == current ? 2 : 0; + while (1) { int ret; - if (!fn(data, frame->pc)) + if (skip) + skip--; + else if (!fn(data, frame->pc)) break; ret = unwind_frame(tsk, frame); if (ret < 0)
--
Catalin
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