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Subject[PATCH 3/8] hugetlb: add per-hstate mutex to synchronize user adjustments
The helper routine hstate_next_node_to_alloc accesses and modifies the
hstate variable next_nid_to_alloc. The helper is used by the routines
alloc_pool_huge_page and adjust_pool_surplus. adjust_pool_surplus is
called with hugetlb_lock held. However, alloc_pool_huge_page can not
be called with the hugetlb lock held as it will call the page allocator.
Two instances of alloc_pool_huge_page could be run in parallel or
alloc_pool_huge_page could run in parallel with adjust_pool_surplus
which may result in the variable next_nid_to_alloc becoming invalid
for the caller and pages being allocated on the wrong node.

Both alloc_pool_huge_page and adjust_pool_surplus are only called from
the routine set_max_huge_pages after boot. set_max_huge_pages is only
called as the reusult of a user writing to the proc/sysfs nr_hugepages,
or nr_hugepages_mempolicy file to adjust the number of hugetlb pages.

It makes little sense to allow multiple adjustment to the number of
hugetlb pages in parallel. Add a mutex to the hstate and use it to only
allow one hugetlb page adjustment at a time. This will synchronize
modifications to the next_nid_to_alloc variable.

Signed-off-by: Mike Kravetz <>
include/linux/hugetlb.h | 1 +
mm/hugetlb.c | 5 +++++
2 files changed, 6 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index a7f7d5f328dc..8817ec987d68 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -566,6 +566,7 @@ HPAGEFLAG(Freed, freed)
#define HSTATE_NAME_LEN 32
/* Defines one hugetlb page size */
struct hstate {
+ struct mutex mutex;
int next_nid_to_alloc;
int next_nid_to_free;
unsigned int order;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f9ba63fc1747..404b0b1c5258 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2616,6 +2616,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
return -ENOMEM;

+ /* mutex prevents concurrent adjustments for the same hstate */
+ mutex_lock(&h->mutex);

@@ -2648,6 +2650,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
if (count > persistent_huge_pages(h)) {
+ mutex_unlock(&h->mutex);
return -EINVAL;
@@ -2722,6 +2725,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
h->max_huge_pages = persistent_huge_pages(h);
+ mutex_unlock(&h->mutex);


@@ -3209,6 +3213,7 @@ void __init hugetlb_add_hstate(unsigned int order)
BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
BUG_ON(order == 0);
h = &hstates[hugetlb_max_hstate++];
+ mutex_init(&h->mutex);
h->order = order;
h->mask = ~(huge_page_size(h) - 1);
for (i = 0; i < MAX_NUMNODES; ++i)
 \ /
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