Re: [PATCH] cxl/core: fix test_bit misuse with CXL_DECODER_F_ bitmask flags

[Cheatham, Benjamin]

On 2/20/2026 8:18 PM, Gregory Price wrote:
> CXL_DECODER_F_LOCK (BIT(4) = 16) and CXL_DECODER_F_NORMALIZED_ADDRESSING
> (BIT(6) = 64) are bit masks, but three call sites pass them to test_bit()
> which expects a bit number.
> 
> Replace test_bit() with direct bitmask tests, consistent with every other
> use of these flags.
> 
> Fixes: 2230c4bdc412 ("cxl: Add handling of locked CXL decoder")
> Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>

Alison sent out a patch [1] two weeks ago for this. I suspect you found this bug
independently, so I figured I should point it out. Otherwise, I would add a Reported-by (or some
other tag) with her name.

Thanks,
Ben

[1]: https://lore.kernel.org/linux-cxl/20260206181404.1025991-1-alison.schofield@xxxxxxxxx/
> ---
>  drivers/cxl/core/hdm.c    | 2 +-
>  drivers/cxl/core/region.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index b2db5967f5c0..c8fcb9d9aa3d 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -904,7 +904,7 @@ static void cxl_decoder_reset(struct cxl_decoder *cxld)
>  	if ((cxld->flags & CXL_DECODER_F_ENABLE) == 0)
>  		return;
>  
> -	if (test_bit(CXL_DECODER_F_LOCK, &cxld->flags))
> +	if (cxld->flags & CXL_DECODER_F_LOCK)
>  		return;
>  
>  	if (port->commit_end == id)
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index bd4c4a4a27da..385be9cb44cd 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -1100,12 +1100,12 @@ static int cxl_rr_assign_decoder(struct cxl_port *port, struct cxl_region *cxlr,
>  static void cxl_region_setup_flags(struct cxl_region *cxlr,
>  				   struct cxl_decoder *cxld)
>  {
> -	if (test_bit(CXL_DECODER_F_LOCK, &cxld->flags)) {
> +	if (cxld->flags & CXL_DECODER_F_LOCK) {
>  		set_bit(CXL_REGION_F_LOCK, &cxlr->flags);
>  		clear_bit(CXL_REGION_F_NEEDS_RESET, &cxlr->flags);
>  	}
>  
> -	if (test_bit(CXL_DECODER_F_NORMALIZED_ADDRESSING, &cxld->flags))
> +	if (cxld->flags & CXL_DECODER_F_NORMALIZED_ADDRESSING)
>  		set_bit(CXL_REGION_F_NORMALIZED_ADDRESSING, &cxlr->flags);
>  }
>