Re: [PATCH -V9 04/15] hugetlb: use mmu_gather instead of a temporary linked list for accumulating pages
From: Michal Hocko <hidden>
Date: 2012-06-14 07:14:28
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On Wed 13-06-12 22:13:00, Aneesh Kumar K.V wrote:
Michal Hocko [off-list ref] writes:quoted
On Wed 13-06-12 16:59:23, Michal Hocko wrote:quoted
On Wed 13-06-12 15:57:23, Aneesh Kumar K.V wrote:quoted
From: "Aneesh Kumar K.V" <redacted> Use a mmu_gather instead of a temporary linked list for accumulating pages when we unmap a hugepage rangeSorry for coming up with the comment that late but you owe us an explanation _why_ you are doing this. I assume that this fixes a real problem when we take i_mmap_mutex already up in unmap_mapping_range mutex_lock(&mapping->i_mmap_mutex); unmap_mapping_range_tree | unmap_mapping_range_list unmap_mapping_range_vma zap_page_range_single unmap_single_vma unmap_hugepage_range mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex); And that this should have been marked for stable as well (I haven't checked when this has been introduced). But then I do not see how this help when you still do this: [...]quoted
diff --git a/mm/memory.c b/mm/memory.c index 1b7dc66..545e18a 100644 --- a/mm/memory.c +++ b/mm/memory.c@@ -1326,8 +1326,11 @@ static void unmap_single_vma(struct mmu_gather *tlb, * Since no pte has actually been setup, it is * safe to do nothing in this case. */ - if (vma->vm_file) - unmap_hugepage_range(vma, start, end, NULL); + if (vma->vm_file) { + mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex); + __unmap_hugepage_range(tlb, vma, start, end, NULL); + mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex); + } } else unmap_page_range(tlb, vma, start, end, details); }Ahhh, you are removing the lock in the next patch. Really confusing and not nice for the stable backport. Could you merge those two patches and add Cc: stable? Then you can add my Reviewed-by: Michal Hocko <redacted>In the last review cycle I was asked to see if we can get a lockdep report for the above and what I found was we don't really cause the above deadlock with the current codebase because for hugetlb we don't directly call unmap_mapping_range.
Ahh, ok I missed that.
But still it is good to remove the i_mmap_mutex, because we don't need that protection now. I didn't mark it for stable because of the above reason.
Thanks for clarification
-aneesh
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