linux-kernel - Re: [PATCH] staging: lustre/lustre/libcfs: Fix type mismatch reported by sparse

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Date:	Tue, 22 Dec 2015 18:35:21 +0530
From:	Niranjan Dighe <niranjan.dighe@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Oleg Drokin <oleg.drokin@...el.com>,
	Andreas Dilger <andreas.dilger@...el.com>,
	Dmitry Eremin <dmitry.eremin@...el.com>,
	James Simmons <jsimmons@...radead.org>,
	Mike Rapoport <mike.rapoport@...il.com>,
	Patrick Boettcher <patrick.boettcher@...teo.de>,
	Matthew Tyler <matt.tyler@...shics.com>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	lustre-devel@...ts.lustre.org
Subject: Re: [PATCH] staging: lustre/lustre/libcfs: Fix type mismatch reported
 by sparse

On Tue, Dec 22, 2015 at 5:14 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Wed, Dec 09, 2015 at 10:38:13PM +0530, Niranjan Dighe wrote:
>> The third argument to function kportal_memhog_alloc is expected to
>> be gfp_t whereas the actual argument was unsigned int. Fix this by
>> explicitly typecasting to gfp_t
>>
>> Signed-off-by: Niranjan Dighe <niranjan.dighe@...il.com>
>> ---
>>  drivers/staging/lustre/lustre/libcfs/module.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/lustre/lustre/libcfs/module.c b/drivers/staging/lustre/lustre/libcfs/module.c
>> index 96d9d46..9c79f6e 100644
>> --- a/drivers/staging/lustre/lustre/libcfs/module.c
>> +++ b/drivers/staging/lustre/lustre/libcfs/module.c
>> @@ -268,7 +268,7 @@ static int libcfs_ioctl_int(struct cfs_psdev_file *pfile, unsigned long cmd,
>>                       /* XXX The ioc_flags is not GFP flags now, need to be fixed */
>>                       err = kportal_memhog_alloc(pfile->private_data,
>>                                                  data->ioc_count,
>> -                                                data->ioc_flags);
>> +                                     (__force gfp_t)data->ioc_flags);
>
> No, please fix the type to be correct properly, like the comment says
> needs to be done.
>
> thanks,
>
> greg k-h

Hello Greg,

I could see that the ioc_flags member of the struct libcfs_ioctl_data
is used as gfp_t only in the
case of the ioctl IOC_LIBCFS_MEMHOG. I can think of following ways to
correct it -

1. Create a union that has 2 different types encapsulated, something like this -
        union {
                __u32 ioc_flags;
                gfp_t alloc_flags;
        }flags;
Because, the ioc_flags seems to be used in different contexts at
different places throughout the
drivers/staging/lustre directory.

2. Is it OK to hardcode the appropriate gfp_t flags for the
IOC_LIBCFS_MEMHOG, as the userspace
seems to be taking the decision about the page allocation
zone/strategy, is this what is intended?


Regards,
Niranjan Dighe
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