linux-kernel - Re: [PATCH] Fix get_unmapped_area and fsync for hugetlb shm segments

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Date:	Wed, 07 Mar 2007 17:26:48 -0600
From:	Adam Litke <agl@...ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Bill Irwin <bill.irwin@...cle.com>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] Fix get_unmapped_area and fsync for hugetlb shm
	segments

On Wed, 2007-03-07 at 16:03 -0700, Eric W. Biederman wrote:
> Bill Irwin <bill.irwin@...cle.com> writes:
> 
> > On Thu, Mar 01, 2007 at 03:46:08PM -0800, Adam Litke wrote:
> >>  static inline int is_file_hugepages(struct file *file)
> >>  {
> >> -	return file->f_op == &hugetlbfs_file_operations;
> >> +	if (file->f_op == &hugetlbfs_file_operations)
> >> +		return 1;
> >> +	if (is_file_shm_hugepages(file))
> >> +		return 1;
> >> +
> >> +	return 0;
> >>  }
> > ...
> >> +int is_file_shm_hugepages(struct file *file)
> >> +{
> >> +	int ret = 0;
> >> +
> >> +	if (file->f_op == &shm_file_operations) {
> >> +		struct shm_file_data *sfd;
> >> +		sfd = shm_file_data(file);
> >> +		ret = is_file_hugepages(sfd->file);
> >> +	}
> >> +	return ret;
> >
> > A comment to prepare others for the impending doubletake might be nice.
> > Or maybe just open-coding the equality check for &huetlbfs_file_operations
> > in is_file_shm_hugepages() if others find it as jarring as I. Please
> > extend my ack to any follow-up fiddling with that.
> 
> You did notice we are testing a different struct file?
> 
> > The patch addresses relatively straightforward issues and naturally at
> > that.
> 
> The whole concept is recursive so I'm not certain being a recursive check
> is that bad but I understand the point.
> 
> I think the right answer is most likely to add an extra file method or
> two so we can remove the need for is_file_hugepages.
> 
> There are still 4 calls to is_file_hugepages in ipc/shm.c and
> 2 calls in mm/mmap.c not counting the one in is_file_shm_hugepages.
> 
> The special cases make it difficult to properly wrap hugetlbfs files
> with another file, which is why we have the weird special case above.

:) Enter my remove-is_file_hugepages() patches (which I posted a few
weeks ago).  I'll rework them and repost soon.  That should help to make
all of this cleaner.

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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