Re: [PATCH v2 3/3] arm64: stacktrace: Convert to ARCH_STACKWALK

On Wed, Sep 02, 2020 at 11:32:13AM +0200, Miroslav Benes wrote:

Hi,

it could be a silly question, but better to ask...

quoted

+	if (regs)
+		start_backtrace(&frame, regs->regs[29], regs->pc);
+	else
+		start_backtrace(&frame, thread_saved_fp(task),
+				thread_saved_pc(task));

Would this also work for task == current? Given that the original code had

quoted

-		start_backtrace(&frame,
-				(unsigned long)__builtin_frame_address(0),
-				(unsigned long)__save_stack_trace);

Oh whoops; I'm annoyed I didn't spot that.

With that gone this cannot work for (task == current && regs == NULL), as
we'll erroneously use stale values from the task struct.

It looks like the LKDTM tests only trigger cases with non-NULL regs, but
IIUC this should show up with show_stack(NULL, NULL, KERN_INFO), as
drivers/tty/sysrq.c does for other cpus.

Thanks,
Mark.

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