Re: [PATCH] dma-debug: fix debugfs initialization order

[Robin Murphy]

On 2021-07-22 10:18, Anthony Iliopoulos wrote:
> Due to link order, dma_debug_init is called before debugfs has a chance
> to initialize (via debugfs_init which also happens in the core initcall
> stage), so the directories for dma-debug are never created.
>
> Move the dma_debug_init initcall from core to postcore stage so that
> debugfs will already be initialized by the time this is called, making
> it oblivious to link-ordering.

Playing initcall chicken here doesn't work so well - the later you 
initialise dma-debug itself, the more chance it has to miss early 
mappings and raise false positives later. As discussed previously[1] the 
better solution would be to decouple the debugfs setup so that just that 
part can be deferred until core_initcall_sync or later.

Robin.

[1] https://lore.kernel.org/linux-iommu/YIgGa6yF%2Fadg8OSN@xxxxxxxxx/

> Fixes: 15b28bbcd567 ("dma-debug: move initialization to common code")
> Signed-off-by: Anthony Iliopoulos <ailiop@xxxxxxxx>
> ---
>   kernel/dma/debug.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> index 14de1271463f..49d80ef7f995 100644
> --- a/kernel/dma/debug.c
> +++ b/kernel/dma/debug.c
> @@ -915,7 +915,7 @@ static int dma_debug_init(void)
>   	pr_info("debugging enabled by kernel config\n");
>   	return 0;
>   }
> -core_initcall(dma_debug_init);
> +postcore_initcall(dma_debug_init);
>   
>   static __init int dma_debug_cmdline(char *str)
>   {