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    SubjectRe: [regression 4.2-rc3] loop: xfstests xfs/073 deadlocked in low memory conditions
    On Wed, Jul 29, 2015 at 01:54:12PM +0200, Michal Hocko wrote:
    > On Tue 21-07-15 10:58:59, Michal Hocko wrote:
    > > [CCing more people from a potentially affected fs - the reference to the
    > > email thread is: http://marc.info/?l=linux-mm&m=143744398020147&w=2]
    ...
    > > > The didn't used to happen, because the loop device used to issue
    > > > reads through the splice path and that does:
    > > >
    > > > error = add_to_page_cache_lru(page, mapping, index,
    > > > GFP_KERNEL & mapping_gfp_mask(mapping));
    > > >
    > > > i.e. it pays attention to the allocation context placed on the
    > > > inode and so is doing GFP_NOFS allocations here and avoiding the
    > > > recursion problem.
    > > >
    > > > [ CC'd Michal Hocko and the mm list because it's a clear exaple of
    > > > why ignoring the mapping gfp mask on any page cache allocation is
    > > > a landmine waiting to be tripped over. ]
    > >
    > > Thank you for CCing me. I haven't noticed this one when checking for
    > > other similar hardcoded GFP_KERNEL users (6afdb859b710 ("mm: do not
    > > ignore mapping_gfp_mask in page cache allocation paths")). And there
    > > seem to be more of them now that I am looking closer.
    > >
    > > I am not sure what to do about fs/nfs/dir.c:nfs_symlink which doesn't
    > > require GFP_NOFS or mapping gfp mask for other allocations in the same
    > > context.
    > >
    > > What do you think about this preliminary (and untested) patch?
    >
    > Dave, did you have chance to test the patch in your environment? Is the
    > patch good to go or we want a larger refactoring?

    No, I haven't had a chance to test it yet. I'll try to get somethign
    done by the end of the week, but I'm not able to reliably
    reproduce the hang I saw (i.e. the analysis I did was from the first
    deadlock and I've only seen it once since) so testing is likely to
    be inconclusive, anyway....

    Cheers,

    Dave.
    --
    Dave Chinner
    david@fromorbit.com


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