Messages in this thread Patch in this message |  | | | Date | Fri, 18 Nov 2005 19:09:50 -0800 | | From | Andrew Morton <> | | Subject | Re: [PATCH] Fix race in set_max_huge_pages for multiple updaters of nr_huge_pages |
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Eric Paris <eparis@redhat.com> wrote: > > If there are multiple updaters to /proc/sys/vm/nr_hugepages > simultaneously it is possible for the nr_huge_pages variable to become > incorrect. There is no locking in the set_max_huge_pages function > around alloc_fresh_huge_page which is able to update nr_huge_pages. Two > callers to alloc_fresh_huge_page could race against each other as could > a call to alloc_fresh_huge_page and a call to update_and_free_page. > This patch just expands the area covered by the hugetlb_lock to cover > the call into alloc_fresh_huge_page. I'm not sure how we could say that > a sysctl section is performance critical where more specific locking > would be needed. > > My reproducer was to run a couple copies of the following script > simultaneously > > while [ true ]; do > echo 1000 > /proc/sys/vm/nr_hugepages > echo 500 > /proc/sys/vm/nr_hugepages > echo 750 > /proc/sys/vm/nr_hugepages > echo 100 > /proc/sys/vm/nr_hugepages > echo 0 > /proc/sys/vm/nr_hugepages > done > > and then watch /proc/meminfo and eventually you will see things like > > HugePages_Total: 100 > HugePages_Free: 109 > > After applying the patch all seemed well. > > Signed-off-by: Eric Paris <eparis@redhat.com> > ---- > > hugetlb.c | 10 +++++++--- > 1 files changed, 7 insertions(+), 3 deletions(-) > > --- linux-2.6.14.2/mm/hugetlb.c.old > +++ linux-2.6.14.2/mm/hugetlb.c > @@ -22,6 +22,7 @@ > static struct list_head hugepage_freelists[MAX_NUMNODES]; > static unsigned int nr_huge_pages_node[MAX_NUMNODES]; > static unsigned int free_huge_pages_node[MAX_NUMNODES]; > +/* This lock protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages */ > static DEFINE_SPINLOCK(hugetlb_lock); > > static void enqueue_huge_page(struct page *page) > @@ -172,10 +173,13 @@ > static unsigned long set_max_huge_pages(unsigned long count) > { > while (count > nr_huge_pages) { > - struct page *page = alloc_fresh_huge_page(); > - if (!page) > - return nr_huge_pages; > + struct page *page; > spin_lock(&hugetlb_lock); > + page = alloc_fresh_huge_page(); > + if (!page) { > + spin_unlock(&hugetlb_lock); > + return nr_huge_pages; > + } > enqueue_huge_page(page); > spin_unlock(&hugetlb_lock); > }
Nope, alloc_fresh_huge_page() does a GFP_HIGHUSER allocation, which can sleep and may not be called inside spinlock. You would have seen a spew of might_sleep() warnings if this was tested with the appropriate kernel debugging options.
How about this?
--- devel/mm/hugetlb.c~hugetlb-fix-race-in-set_max_huge_pages-for-multiple-updaters-of-nr_huge_pages 2005-11-18 19:04:10.000000000 -0800 +++ devel-akpm/mm/hugetlb.c 2005-11-18 19:07:26.000000000 -0800 @@ -22,6 +22,10 @@ unsigned long max_huge_pages; static struct list_head hugepage_freelists[MAX_NUMNODES]; static unsigned int nr_huge_pages_node[MAX_NUMNODES]; static unsigned int free_huge_pages_node[MAX_NUMNODES]; + +/* + * Protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages + */ static DEFINE_SPINLOCK(hugetlb_lock); static void enqueue_huge_page(struct page *page) @@ -61,8 +65,10 @@ static struct page *alloc_fresh_huge_pag HUGETLB_PAGE_ORDER); nid = (nid + 1) % num_online_nodes(); if (page) { + spin_lock(&hugetlb_lock); nr_huge_pages++; nr_huge_pages_node[page_to_nid(page)]++; + spin_unlock(&hugetlb_lock); } return page; } _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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