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    SubjectRe: [PATCH] VM: Fix the gfp_mask in invalidate_complete_page2
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    On Fri, 2006-10-06 at 17:49 -0400, Steve Dickson wrote:
    > Trond Myklebust wrote:
    > > If try_to_release_page() is called with a zero gfp mask, then the
    > > filesystem is effectively denied the possibility of sleeping while
    > > attempting to release the page. There doesn't appear to be any valid
    > > reason why this should be banned, given that we're not calling this from
    > > a memory allocation context.
    > >
    > > For this reason, change the gfp_mask argument of the call to GFP_KERNEL.
    > >
    > > Note: I am less sure of what the callers of invalidate_complete_page()
    > > require, and so this patch does not touch that mask.
    > >
    > > Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
    > > ---
    > > diff --git a/mm/truncate.c b/mm/truncate.c
    > > index f4edbc1..49c1ffd 100644
    > > --- a/mm/truncate.c
    > > +++ b/mm/truncate.c
    > > @@ -302,7 +302,7 @@ invalidate_complete_page2(struct address
    > > if (page->mapping != mapping)
    > > return 0;
    > >
    > > - if (PagePrivate(page) && !try_to_release_page(page, 0))
    > > + if (PagePrivate(page) && !try_to_release_page(page, GFP_KERNEL))
    > > return 0;
    > >
    > > write_lock_irq(&mapping->tree_lock);
    > Well I was using mapping_gfp_mask(mapping) as the argument to
    > try_to_release_page() which also worked... but isn't this
    > just plugging one of many holes?

    Yeah using mapping_gfp_mask(mapping) sounds like a better option.

    ...and yes, there are other callers that need to be audited. I'm
    particularly curious about the effect of the call in
    block_invalidatepage() on XFS, which has a similar test to ours.

    The call in fallback_migrate_page() should probably be using
    mapping_gfp_mask() too.

    > Meaning try_to_release_page is called
    > from a number of places with a zero gfp_mask so shouldn't those
    > also be fixed as well OR removed the gfp_mask as an argument as the
    > comment at the top of try_to_release_page() alludes to?

    Nope. In order to make it work correctly with NFS and XFS, all calls to
    try_to_release_page() would have to be allowed to be blocking. The
    problem is that shrink_page_list() still wants to call
    try_to_release_page() from a memory allocation context.

    Cheers,
    Trond
    -
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