Gregory Price <gourry.memverge@xxxxxxxxx> writes:
> In the event of rebind, pol->nodemask can change at the same time as an
> allocation occurs. We can detect this with tsk->mems_allowed_seq and
> prevent a miscount or an allocation failure from occurring.
>
> The same thing happens in the allocators to detect failure, but this
> can prevent spurious failures in a much smaller critical section.
>
> Suggested-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Signed-off-by: Gregory Price <gregory.price@xxxxxxxxxxxx>
> ---
> mm/mempolicy.c | 31 +++++++++++++++++++++++++------
> 1 file changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index d8cc3a577986..ed0d5d2d456a 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1878,11 +1878,17 @@ bool apply_policy_zone(struct mempolicy *policy, enum zone_type zone)
>
> static unsigned int weighted_interleave_nodes(struct mempolicy *policy)
> {
> - unsigned int node = current->il_prev;
> -
> - if (!current->il_weight || !node_isset(node, policy->nodes)) {
> + unsigned int node;
> + unsigned int cpuset_mems_cookie;
> +
> +retry:
> + /* to prevent miscount use tsk->mems_allowed_seq to detect rebind */
> + cpuset_mems_cookie = read_mems_allowed_begin();
> + node = current->il_prev;
> + if (!node || !node_isset(node, policy->nodes)) {
~~~~~
!current->il_weight ?
--
Best Regards,
Huang, Ying
> node = next_node_in(node, policy->nodes);
> - /* can only happen if nodemask is being rebound */
> + if (read_mems_allowed_retry(cpuset_mems_cookie))
> + goto retry;
> if (node == MAX_NUMNODES)
> return node;
> current->il_prev = node;
> @@ -1896,8 +1902,14 @@ static unsigned int weighted_interleave_nodes(struct mempolicy *policy)
> static unsigned int interleave_nodes(struct mempolicy *policy)
> {
> unsigned int nid;
> + unsigned int cpuset_mems_cookie;
> +
> + /* to prevent miscount, use tsk->mems_allowed_seq to detect rebind */
> + do {
> + cpuset_mems_cookie = read_mems_allowed_begin();
> + nid = next_node_in(current->il_prev, policy->nodes);
> + } while (read_mems_allowed_retry(cpuset_mems_cookie));
>
> - nid = next_node_in(current->il_prev, policy->nodes);
> if (nid < MAX_NUMNODES)
> current->il_prev = nid;
> return nid;
> @@ -2374,6 +2386,7 @@ static unsigned long alloc_pages_bulk_array_weighted_interleave(gfp_t gfp,
> struct page **page_array)
> {
> struct task_struct *me = current;
> + unsigned int cpuset_mems_cookie;
> unsigned long total_allocated = 0;
> unsigned long nr_allocated = 0;
> unsigned long rounds;
> @@ -2391,7 +2404,13 @@ static unsigned long alloc_pages_bulk_array_weighted_interleave(gfp_t gfp,
> if (!nr_pages)
> return 0;
>
> - nnodes = read_once_policy_nodemask(pol, &nodes);
> + /* read the nodes onto the stack, retry if done during rebind */
> + do {
> + cpuset_mems_cookie = read_mems_allowed_begin();
> + nnodes = read_once_policy_nodemask(pol, &nodes);
> + } while (read_mems_allowed_retry(cpuset_mems_cookie));
> +
> + /* if the nodemask has become invalid, we cannot do anything */
> if (!nnodes)
> return 0;
