Re: [PATCH v2] arm64: Fix task tracing

From: Catalin Marinas
Date: Mon Apr 15 2013 - 06:15:14 EST


On Tue, Apr 09, 2013 at 01:33:34PM +0100, Christopher Covington wrote:
> For accurate accounting pass contextidr_thread_switch the prev
> task pointer, since cpu_switch_to has at that point changed the
> the stack pointer.
>
> Signed-off-by: Christopher Covington <cov@xxxxxxxxxxxxxx>
> ---
> arch/arm64/kernel/process.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 0337cdb..a49b25a 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -315,7 +315,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
> /* the actual thread switch */
> last = cpu_switch_to(prev, next);
>
> - contextidr_thread_switch(next);
> + contextidr_thread_switch(prev);

The original code was indeed wrong but using prev isn't any better. For
a newly created thread, prev is probably 0 (if it's in a register,
cpu_context has been zeroed by copy_thread()) or some random stack
value.

So we either use current or move the call before cpu_switch_to() (I
would go for the former).

--
Catalin
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