[PATCH v5 4/4] mm/mempolicy: protect task interleave functions with tsk->mems_allowed_seq
From: Gregory Price <hidden>
Date: 2024-02-02 17:03:01
Also in:
linux-doc, linux-fsdevel, linux-mm, lkml
Subsystem:
memory management, memory management - memory policy and migration, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
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" <redacted> Signed-off-by: Gregory Price <redacted> --- 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)) { 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;
--
2.39.1