linux-kernel - Re: [PATCH -next] pci: fix a -Wtype-limits compilation warning

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Message-ID: <c2908ed5-b0a7-74a7-7d03-84ad38e1a95a@deltatee.com>
Date:   Wed, 18 Dec 2019 10:22:31 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Qian Cai <cai@....pw>, bhelgaas@...gle.com
Cc:     jamessewart@...sta.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] pci: fix a -Wtype-limits compilation warning



On 2019-12-18 10:00 a.m., Qian Cai wrote:
> The commit a7d06153eea2 ("PCI: Fix pci_add_dma_alias() bitmask size")
> introduced a compilation warning and a potential infinite loop because
> it is no longer possible to be self-terminated as u8 is always less than
> 256,
> 
> In file included from ./include/linux/kernel.h:12,
>                  from ./include/asm-generic/bug.h:19,
>                  from ./arch/x86/include/asm/bug.h:83,
>                  from ./include/linux/bug.h:5,
>                  from ./include/linux/jump_label.h:250,
>                  from ./arch/x86/include/asm/string_64.h:6,
>                  from ./arch/x86/include/asm/string.h:5,
>                  from ./include/linux/string.h:20,
>                  from ./include/linux/uuid.h:12,
>                  from ./include/linux/mod_devicetable.h:13,
>                  from ./include/linux/pci.h:27,
>                  from drivers/pci/search.c:11:
> drivers/pci/search.c: In function 'pci_for_each_dma_alias':
> ./include/linux/bitops.h:30:13: warning: comparison is always true due
> to limited range of data type [-Wtype-limits]
>        (bit) < (size);     \
>              ^
> drivers/pci/search.c:46:3: note: in expansion of macro 'for_each_set_bit'
>    for_each_set_bit(devfn, pdev->dma_alias_mask, MAX_NR_DEVFNS) {
> 
> Fixed it by using u16 for "devfn" in this occasion.
> 
> Fixes: a7d06153eea2 ("PCI: Fix pci_add_dma_alias() bitmask size")
> Signed-off-by: Qian Cai <cai@....pw>

Makes sense to me,

Reviewed-by: Logan Gunthorpe <logang@...tatee.com>


> ---
>  drivers/pci/search.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> index 9e4dfae47252..42bc44d0e681 100644
> --- a/drivers/pci/search.c
> +++ b/drivers/pci/search.c
> @@ -41,7 +41,7 @@ int pci_for_each_dma_alias(struct pci_dev *pdev,
>  	 * DMA, iterate over that too.
>  	 */
>  	if (unlikely(pdev->dma_alias_mask)) {
> -		u8 devfn;
> +		u16 devfn;
>  
>  		for_each_set_bit(devfn, pdev->dma_alias_mask, MAX_NR_DEVFNS) {
>  			ret = fn(pdev, PCI_DEVID(pdev->bus->number, devfn),
>