On Thu, 19 Apr 2018 12:12:38 -0400 (EDT) Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> The kvmalloc function tries to use kmalloc and falls back to vmalloc if
> kmalloc fails.
>
> Unfortunatelly, some kernel code has bugs - it uses kvmalloc and then
> uses DMA-API on the returned memory or frees it with kfree. Such bugs were
> found in the virtio-net driver, dm-integrity or RHEL7 powerpc-specific
> code.
>
> These bugs are hard to reproduce because vmalloc falls back to kmalloc
> only if memory is fragmented.
Yes, that's nasty.
> In order to detect these bugs reliably I submit this patch that changes
> kvmalloc to always use vmalloc if CONFIG_DEBUG_VM is turned on.
>
> ...
>
> --- linux-2.6.orig/mm/util.c 2018-04-18 15:46:23.000000000 +0200
> +++ linux-2.6/mm/util.c 2018-04-18 16:00:43.000000000 +0200
> @@ -395,6 +395,7 @@ EXPORT_SYMBOL(vm_mmap);
> */
> void *kvmalloc_node(size_t size, gfp_t flags, int node)
> {
> +#ifndef CONFIG_DEBUG_VM
> gfp_t kmalloc_flags = flags;
> void *ret;
>
> @@ -426,6 +427,7 @@ void *kvmalloc_node(size_t size, gfp_t f
> */
> if (ret || size <= PAGE_SIZE)
> return ret;
> +#endif
>
> return __vmalloc_node_flags_caller(size, node, flags,
> __builtin_return_address(0));
Well, it doesn't have to be done at compile-time, does it? We could
add a knob (in debugfs, presumably) which enables this at runtime.
That's far more user-friendly.
