Re: [PATCH] list corruption by gather_surplus
From: Aneesh Kumar K.V <hidden>
Date: 2012-07-27 17:52:13
Cliff Wickman [off-list ref] writes:
From: Cliff Wickman <redacted> Gentlemen, I see that you all have done maintenance on mm/hugetlb.c, so I'm hoping one or two of you could comment on a problem and proposed fix. I am seeing list corruption occurring from within gather_surplus_pages() (mm/hugetlb.c). The problem occurs under a heavy load, and seems to be because this function drops the hugetlb_lock. I have CONFIG_DEBUG_LIST=y, and am running an MPI application with 64 threads and a library that creates a large heap of hugetlbfs pages for it. The below patch fixes the problem. The gist of this patch is that gather_surplus_pages() does not have to drop the lock if alloc_buddy_huge_page() is told whether the lock is already held.
But you didn't explain the corruption details right ? What cause the corruption ? It would be nice to document that in the commit.
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But I may be missing some reason why gather_surplus_pages() is unlocking and locking the hugetlb_lock several times (besides around the allocator). Could you take a look and advise? Signed-off-by: Cliff Wickman <redacted> --- mm/hugetlb.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) Index: linux/mm/hugetlb.c ===================================================================--- linux.orig/mm/hugetlb.c +++ linux/mm/hugetlb.c@@ -747,7 +747,9 @@ static int free_pool_huge_page(struct hs return ret; } -static struct page *alloc_buddy_huge_page(struct hstate *h, int nid) +/* already_locked means the caller has already locked hugetlb_lock */ +static struct page *alloc_buddy_huge_page(struct hstate *h, int nid, + int already_locked) {
Why ? Why can't we always call this with lock held ?
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struct page *page; unsigned int r_nid;@@ -778,7 +780,8 @@ static struct page *alloc_buddy_huge_pag * the node values until we've gotten the hugepage and only the
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