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authorAdam Litke <agl@us.ibm.com>2008-03-04 14:29:38 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-03-04 16:35:18 -0800
commitac09b3a15154af5f081fed509c6c3662e79de785 (patch)
tree753170e02fafcadbd525d93b01105a4995d51461
parenta07e6ab41be179cf1ed728a4f41368435508b550 (diff)
downloadkernel-ac09b3a15154af5f081fed509c6c3662e79de785.tar.gz
hugetlb: close a difficult to trigger reservation race
A hugetlb reservation may be inadequately backed in the event of racing allocations and frees when utilizing surplus huge pages. Consider the following series of events in processes A and B: A) Allocates some surplus pages to satisfy a reservation B) Frees some huge pages A) A notices the extra free pages and drops hugetlb_lock to free some of its surplus pages back to the buddy allocator. B) Allocates some huge pages A) Reacquires hugetlb_lock and returns from gather_surplus_huge_pages() Avoid this by commiting the reservation after pages have been allocated but before dropping the lock to free excess pages. For parity, release the reservation in return_unused_surplus_pages(). This patch also corrects the cpuset_mems_nr() error path in hugetlb_acct_memory(). If the cpuset check fails, uncommit the reservation, but also be sure to return any surplus huge pages that may have been allocated to back the failed reservation. Thanks to Andy Whitcroft for discovering this. Signed-off-by: Adam Litke <agl@us.ibm.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Andy Whitcroft <apw@shadowen.org> Cc: Dave Hansen <haveblue@us.ibm.com> Cc: William Lee Irwin III <wli@holomorphy.com> Cc: Andy Whitcroft <apw@shadowen.org> Cc: Mel Gorman <mel@csn.ul.ie> Cc: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/hugetlb.c17
1 files changed, 13 insertions, 4 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 89e6286a7f57..20e04c64468d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -296,8 +296,10 @@ static int gather_surplus_pages(int delta)
int needed, allocated;
needed = (resv_huge_pages + delta) - free_huge_pages;
- if (needed <= 0)
+ if (needed <= 0) {
+ resv_huge_pages += delta;
return 0;
+ }
allocated = 0;
INIT_LIST_HEAD(&surplus_list);
@@ -335,9 +337,12 @@ retry:
* The surplus_list now contains _at_least_ the number of extra pages
* needed to accomodate the reservation. Add the appropriate number
* of pages to the hugetlb pool and free the extras back to the buddy
- * allocator.
+ * allocator. Commit the entire reservation here to prevent another
+ * process from stealing the pages as they are added to the pool but
+ * before they are reserved.
*/
needed += allocated;
+ resv_huge_pages += delta;
ret = 0;
free:
list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
@@ -371,6 +376,9 @@ static void return_unused_surplus_pages(unsigned long unused_resv_pages)
struct page *page;
unsigned long nr_pages;
+ /* Uncommit the reservation */
+ resv_huge_pages -= unused_resv_pages;
+
nr_pages = min(unused_resv_pages, surplus_huge_pages);
while (nr_pages) {
@@ -1205,12 +1213,13 @@ static int hugetlb_acct_memory(long delta)
if (gather_surplus_pages(delta) < 0)
goto out;
- if (delta > cpuset_mems_nr(free_huge_pages_node))
+ if (delta > cpuset_mems_nr(free_huge_pages_node)) {
+ return_unused_surplus_pages(delta);
goto out;
+ }
}
ret = 0;
- resv_huge_pages += delta;
if (delta < 0)
return_unused_surplus_pages((unsigned long) -delta);