Re: [PATCH 2/3] tools: testing: Use existing atomic.h for vma/radix-tree tests

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Wed, Aug 27, 2025 at 11:04:42AM +0000, Brendan Jackman wrote:
> The shared userspace logic used for unit-testing radix-tree and VMA code
> currently has its own replacements for atomics helpers. This is not
> needed as the necessary APIs already have userspace implementations in
> the tools tree. Switching over to that allows deleting a bit of code.
>
> Note that the implementation is different; while the version being
> deleted here is implemented using liburcu, the existing version in tools
> uses either x86 asm or compiler builtins. It's assumed that both are
> equally likely to be correct.
>
> The tools tree's version of atomic_t is a struct type while the version
> being deleted was just a typedef of an integer. This means it's no
> longer valid to call __sync_bool_compare_and_swap() directly on it. One
> option would be to just peek into the struct and call it on the field,
> but it seems a little cleaner to just use the corresponding atomic.h
> API. On non-x86 archs this is implemented using
> __sync_val_compare_and_swap(). It's not clear why the old version uses
> the bool variant instead of the generic "val" one, for now it's assumed
> that this was a mistake.
>
> Signed-off-by: Brendan Jackman <jackmanb@google.com>

OK so on basis you fix Liam + Pedro's comments, feel free to add:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

On respin.

Thanks!

> ---
>  tools/testing/shared/linux/maple_tree.h |  6 ++----
>  tools/testing/vma/linux/atomic.h        | 17 -----------------

Thanks :)

>  tools/testing/vma/vma_internal.h        |  3 ++-
>  3 files changed, 4 insertions(+), 22 deletions(-)
>
> diff --git a/tools/testing/shared/linux/maple_tree.h b/tools/testing/shared/linux/maple_tree.h
> index f67d47d32857cee296c2784da57825c9a31cd340..7d0fadef0f11624dbb110ad351aabdc79a19dcd2 100644
> --- a/tools/testing/shared/linux/maple_tree.h
> +++ b/tools/testing/shared/linux/maple_tree.h
> @@ -1,7 +1,5 @@
>  /* SPDX-License-Identifier: GPL-2.0+ */
> -#define atomic_t int32_t
> -#define atomic_inc(x) uatomic_inc(x)
> -#define atomic_read(x) uatomic_read(x)
> -#define atomic_set(x, y) uatomic_set(x, y)

This is nice!

> +#include <linux/atomic.h>
> +
>  #define U8_MAX UCHAR_MAX
>  #include "../../../../include/linux/maple_tree.h"
> diff --git a/tools/testing/vma/linux/atomic.h b/tools/testing/vma/linux/atomic.h
> deleted file mode 100644
> index 788c597c4fdea7392307de93ff4459453b96179b..0000000000000000000000000000000000000000
> --- a/tools/testing/vma/linux/atomic.h
> +++ /dev/null
> @@ -1,17 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0-or-later */
> -
> -#ifndef _LINUX_ATOMIC_H
> -#define _LINUX_ATOMIC_H
> -
> -#define atomic_t int32_t
> -#define atomic_inc(x) uatomic_inc(x)
> -#define atomic_read(x) uatomic_read(x)
> -#define atomic_set(x, y) uatomic_set(x, y)
> -#define U8_MAX UCHAR_MAX
> -
> -#ifndef atomic_cmpxchg_relaxed
> -#define  atomic_cmpxchg_relaxed		uatomic_cmpxchg
> -#define  atomic_cmpxchg_release         uatomic_cmpxchg
> -#endif /* atomic_cmpxchg_relaxed */
> -
> -#endif	/* _LINUX_ATOMIC_H */

This is also nice!

> diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
> index 3639aa8dd2b06ebe5b9cfcfe6669994fd38c482d..a720a4e6bada83e6b32e76762089eeec35ba8fac 100644
> --- a/tools/testing/vma/vma_internal.h
> +++ b/tools/testing/vma/vma_internal.h
> @@ -21,6 +21,7 @@
>
>  #include <stdlib.h>
>
> +#include <linux/atomic.h>
>  #include <linux/list.h>
>  #include <linux/maple_tree.h>
>  #include <linux/mm.h>
> @@ -1381,7 +1382,7 @@ static inline int mapping_map_writable(struct address_space *mapping)
>  	do {
>  		if (c < 0)
>  			return -EPERM;
> -	} while (!__sync_bool_compare_and_swap(&mapping->i_mmap_writable, c, c+1));
> +	} while (!atomic_cmpxchg(&mapping->i_mmap_writable, c, c+1));

Obv. ref. Pedro's reply.

>
>  	return 0;
>  }
>
> --
> 2.50.1
>