Re: [PATCH 1/2] kcsan: test: Adjust "expect" allocation type for kmalloc_obj

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Feb 27, 2026 at 06:50:20PM +0000, Venkata Swamy Kassa wrote:
> From: Kees Cook <kees@kernel.org>
> 
> The call to kmalloc_obj(observed.lines) returns "char (*)[3][512]",
> a pointer to the whole 2D array. But "expect" wants to be "char (*)[512]",
> the decayed pointer type, as if it were observed.lines itself (though
> without the "3" bounds). This produces the following build error:
> 
> ../kernel/kcsan/kcsan_test.c: In function '__report_matches':
> ../kernel/kcsan/kcsan_test.c:171:16: error: assignment to 'char (*)[512]' from incompatible pointer type 'char (*)[3][512]'
> [-Wincompatible-pointer-types]
>   171 |         expect = kmalloc_obj(observed.lines);
>       |                ^
> 
> Instead of changing the "expect" type to "char (*)[3][512]" and
> requiring a dereference at each use (e.g. "(expect*)[0]"), just
> explicitly cast the return to the desired type.
> 
> Note that I'm intentionally not switching back to byte-based "kmalloc"
> here because I cannot find a way for the Coccinelle script (which will
> be used going forward to catch future conversions) to exclude this case.
> 
> Tested with:
> 
> $ ./tools/testing/kunit/kunit.py run \
> 	--kconfig_add CONFIG_DEBUG_KERNEL=y \
> 	--kconfig_add CONFIG_KCSAN=y \
> 	--kconfig_add CONFIG_KCSAN_KUNIT_TEST=y \
> 	--arch=x86_64 --qemu_args '-smp 2' kcsan
> 
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Fixes: 69050f8d6d07 ("treewide: Replace kmalloc with kmalloc_obj for non-scalar types")
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
>  kernel/kcsan/kcsan_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
> index 79e655ea4ca1..ae758150ccb9 100644
> --- a/kernel/kcsan/kcsan_test.c
> +++ b/kernel/kcsan/kcsan_test.c
> @@ -168,7 +168,7 @@ static bool __report_matches(const struct expect_report *r)
>  	if (!report_available())
>  		return false;
>  
> -	expect = kmalloc_obj(observed.lines);
> +	expect = (typeof(expect))kmalloc_obj(observed.lines);
>  	if (WARN_ON(!expect))
>  		return false;
>  
> -- 
> 2.43.0
> 
> 

Why was this part of a usb patch series?

thanks,

greg k-h