Re: [PATCH 19/26] percpu: clean up all mappings when pcpu_map_pages() fails

[Yosry Ahmed]

On Fri, Jul 12, 2024 at 10:01 AM Brendan Jackman <jackmanb@xxxxxxxxxx> wrote:
>
> From: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
>
> In pcpu_map_pages(), if __pcpu_map_pages() fails on a CPU, we call
> __pcpu_unmap_pages() to clean up mappings on all CPUs where mappings
> were created, but not on the CPU where __pcpu_map_pages() fails.
>
> __pcpu_map_pages() and __pcpu_unmap_pages() are wrappers around
> vmap_pages_range_noflush() and vunmap_range_noflush(). All other callers
> of vmap_pages_range_noflush() call vunmap_range_noflush() when mapping
> fails, except pcpu_map_pages(). The reason could be that partial
> mappings may be left behind from a failed mapping attempt.
>
> Call __pcpu_unmap_pages() for the failed CPU as well in
> pcpu_map_pages().
>
> This was found by code inspection, no failures or bugs were observed.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> Acked-by: Dennis Zhou <dennis@xxxxxxxxxx>
>
> (am from https://lore.kernel.org/lkml/20240311194346.2291333-1-yosryahmed@xxxxxxxxxx/)

This went into v6.10 as commit 2ccd48ce35e87f09472b42dda96fbf7b5165f3c3.

> ---
>  mm/percpu-vm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> index 2054c9213c43..cd69caf6aa8d 100644
> --- a/mm/percpu-vm.c
> +++ b/mm/percpu-vm.c
> @@ -231,10 +231,10 @@ static int pcpu_map_pages(struct pcpu_chunk *chunk,
>         return 0;
>  err:
>         for_each_possible_cpu(tcpu) {
> -               if (tcpu == cpu)
> -                       break;
>                 __pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),
>                                    page_end - page_start);
> +               if (tcpu == cpu)
> +                       break;
>         }
>         pcpu_post_unmap_tlb_flush(chunk, page_start, page_end);
>         return err;
>
> --
> 2.45.2.993.g49e7a77208-goog
>