On Mon, Mar 11, 2024 at 07:23:30PM +0800, Changbin Du wrote:
> This disables msan check for preempt_count_{add,sub} to fix a
> instrumentation recursion issue on preempt_count:
>
> __msan_metadata_ptr_for_load_4() -> kmsan_virt_addr_valid() ->
> preempt_disable() -> __msan_metadata_ptr_for_load_4()
>
> With this fix, I was able to run kmsan kernel with:
> o CONFIG_DEBUG_KMEMLEAK=n
> o CONFIG_KFENCE=n
> o CONFIG_LOCKDEP=n
>
> KMEMLEAK and KFENCE generate too many false positives in unwinding code.
> LOCKDEP still introduces instrumenting recursions issue. But these are
> other issues expected to be fixed.
>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Signed-off-by: Changbin Du <changbin.du@xxxxxxxxxx>
> ---
> kernel/sched/core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9116bcc90346..5b63bb98e60a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5848,7 +5848,7 @@ static inline void preempt_latency_start(int val)
> }
> }
>
> -void preempt_count_add(int val)
> +void __no_kmsan_checks preempt_count_add(int val)
> {
> #ifdef CONFIG_DEBUG_PREEMPT
> /*
> @@ -5880,7 +5880,7 @@ static inline void preempt_latency_stop(int val)
> trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
> }
What prevents a larger loop via one of the calles of preempt_count_{add,sub}()
For example, via preempt_latency_{start,stop}() ?
... or via some *other* instrumentation that might be placed in those?
I suspect we should be using noinstr or __always_inline in a bunch of places to
clean this up properly.
Mark.
