Re: [PATCH 6/6] Mlock: make mlock error return Posixly Correct

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Wed, 2008-08-20 at 17:35 +0900, KOSAKI Motohiro wrote:
> > From:  KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > 
> > Against:  2.6.27-rc3-mmotm-080816-0202
> > 
> > Rework Posix error return for mlock().
> > 
> > Translate get_user_pages() error to posix specified error codes.
> > 
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
> > 
> >  mm/memory.c |    2 +-
> >  mm/mlock.c  |   27 ++++++++++++++++++++++++---
> >  2 files changed, 25 insertions(+), 4 deletions(-)
> > 
> > Index: linux-2.6.27-rc3-mmotm/mm/mlock.c
> > ===================================================================
> > --- linux-2.6.27-rc3-mmotm.orig/mm/mlock.c	2008-08-18 15:57:11.000000000 -0400
> > +++ linux-2.6.27-rc3-mmotm/mm/mlock.c	2008-08-18 15:57:39.000000000 -0400
> > @@ -143,6 +143,18 @@ static void munlock_vma_page(struct page
> >  	}
> >  }
> >  
> > +/*
> > + * convert get_user_pages() return value to posix mlock() error
> > + */
> > +static int __mlock_posix_error_return(long retval)
> > +{
> > +	if (retval == -EFAULT)
> > +		retval = -ENOMEM;
> > +	else if (retval == -ENOMEM)
> > +		retval = -EAGAIN;
> > +	return retval;
> > +}
> > +
> >  /**
> >   * __mlock_vma_pages_range() -  mlock/munlock a range of pages in the vma.
> >   * @vma:   target vma
> > @@ -209,8 +221,13 @@ static long __mlock_vma_pages_range(stru
> >  		 * or for addresses that map beyond end of a file.
> >  		 * We'll mlock the the pages if/when they get faulted in.
> >  		 */
> > -		if (ret < 0)
> > +		if (ret < 0) {
> > +			if (vma->vm_flags & VM_NONLINEAR)
> > +				ret = 0;
> > +			else
> > +				ret = __mlock_posix_error_return(ret);
> >  			break;
> > +		}
> >  		if (ret == 0) {
> >  			/*
> >  			 * We know the vma is there, so the only time
> 
> __mlock_vma_pages_range is used by mmap() and mlock().
> 
> mlock case 
> 
> 	sys_mlock
> 		do_mlock
> 			mlock_fixup
> 				__mlock_vma_pages_range
> 
> mmap case
> 
> 	do_mmap_pgoff
> 		mmap_region
> 			mlock_vma_pages_range
> 				__mlock_vma_pages_range
> 
> 
> mlock() need error code if vma permission failure happend.
> but mmap() (and remap_pages_range(), etc..) should ignore it.
> 
> So, mlock_vma_pages_range() should ignore __mlock_vma_pages_range()'s error code.

Well, I don't know whether we can trigger a vma permission failure
during mmap(MAP_LOCKED) or a remap within a VM_LOCKED vma, either of
which will end up calling mlock_vma_pages_range().  However, [after
rereading the man page] looks like we DO want to return any ENOMEM w/o
translating to EAGAIN.  Guess that means I should do the translation
from within for mlock() from within mlock_fixup().  remap_pages_range()
probably wants to explicitly ignore any error from the mlock callout.

Will resend.

Thanks,
Lee

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