Johannes Weiner [off-list ref] writes:

On Sat, Jun 09, 2012 at 02:29:50PM +0530, Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V" <redacted>

i_mmap_mutex lock was added in unmap_single_vma by 502717f4e ("hugetlb:
fix linked list corruption in unmap_hugepage_range()") but we don't use
page->lru in unmap_hugepage_range any more.  Also the lock was taken
higher up in the stack in some code path.  That would result in deadlock.

unmap_mapping_range (i_mmap_mutex)
 -> unmap_mapping_range_tree
    -> unmap_mapping_range_vma
       -> zap_page_range_single
         -> unmap_single_vma
	      -> unmap_hugepage_range (i_mmap_mutex)

For shared pagetable support for huge pages, since pagetable pages are ref
counted we don't need any lock during huge_pmd_unshare.  We do take
i_mmap_mutex in huge_pmd_share while walking the vma_prio_tree in mapping.
(39dde65c9940c97f ("shared page table for hugetlb page")).

Signed-off-by: Aneesh Kumar K.V <redacted>

This patch (together with the previous one) seems like a bugfix that's
not really related to the hugetlb controller, unless I miss something.

Could you please submit the fix separately?

Patches upto 6 can really got in a separate series. I was not sure
whether I should split them. I will post that as a separate series now

Maybe also fold the two patches into one and make it a single bugfix
change that gets rid of the lock by switching away from page->lru.

I wanted to make sure the patch that drop i_mmap_mutex is a separate one
so that we understand and document the locking details separately

-aneesh

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>