@@ -1876,17 +1876,26 @@ unsigned int mempolicy_slab_node(void)
*/
static unsigned offset_il_node(struct mempolicy *pol, unsigned long n)
{
- unsigned nnodes = nodes_weight(pol->nodes);
- unsigned target;
+ nodemask_t nodemask = pol->nodes;
+ unsigned int target, nnodes;
int i;
int nid;
+ /*
+ * The barrier will stabilize the nodemask in a register or on
+ * the stack so that it will stop changing under the code.
+ *
+ * Between first_node() and next_node(), pol->nodes could be changed
+ * by other threads. So we put pol->nodes in a local stack.
+ */
+ barrier();
+ nnodes = nodes_weight(nodemask);
if (!nnodes)
return numa_node_id();
target = (unsigned int)n % nnodes;
- nid = first_node(pol->nodes);
+ nid = first_node(nodemask);
for (i = 0; i < target; i++)
- nid = next_node(nid, pol->nodes);
+ nid = next_node(nid, nodemask);
return nid;
}
The patch titled Subject: mm/mempolicy: fix a race between offset_il_node and mpol_rebind_task has been removed from the -mm tree. Its filename was mm-mempolicy-fix-a-race-between-offset_il_node-and-mpol_rebind_task.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: yanghui <yanghui.def@bytedance.com> Subject: mm/mempolicy: fix a race between offset_il_node and mpol_rebind_task Servers happened below panic: Kernel version:5.4.56 BUG: unable to handle page fault for address: 0000000000002c48 RIP: 0010:__next_zones_zonelist+0x1d/0x40 [264003.977696] RAX: 0000000000002c40 RBX: 0000000000100dca RCX: 0000000000000014 [264003.977872] Call Trace: [264003.977888] __alloc_pages_nodemask+0x277/0x310 [264003.977908] alloc_page_interleave+0x13/0x70 [264003.977926] handle_mm_fault+0xf99/0x1390 [264003.977951] __do_page_fault+0x288/0x500 [264003.977979] ? schedule+0x39/0xa0 [264003.977994] do_page_fault+0x30/0x110 [264003.978010] page_fault+0x3e/0x50 The reason for the panic is that MAX_NUMNODES is passed in the third parameter in __alloc_pages_nodemask(preferred_nid). So access to zonelist->zoneref->zone_idx in __next_zones_zonelist will cause a panic. In offset_il_node(), first_node() returns nid from pol->v.nodes, after this other threads may chang pol->v.nodes before next_node(). This race condition will let next_node return MAX_NUMNODES. So put pol->nodes in a local variable. The race condition is between offset_il_node and cpuset_change_task_nodemask: CPU0: CPU1: alloc_pages_vma() interleave_nid(pol,) offset_il_node(pol,) first_node(pol->v.nodes) cpuset_change_task_nodemask //nodes==0xc mpol_rebind_task mpol_rebind_policy mpol_rebind_nodemask(pol,nodes) //nodes==0x3 next_node(nid, pol->v.nodes)//return MAX_NUMNODES Link: https://lkml.kernel.org/r/20210906034658.48721-1-yanghui.def@bytedance.com Signed-off-by: yanghui <yanghui.def@bytedance.com> Reviewed-by: Muchun Song <songmuchun@bytedance.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/mempolicy.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-)