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 of panic is that MAX_NUMNODES is passd in the third parameter
in function __alloc_pages_nodemask(preferred_nid). So if to access
zonelist->zoneref->zone_idx in __next_zones_zonelist the panic will happen.
In offset_il_node(), first_node() return nid from pol->v.nodes, after
this other threads may changed 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
Signed-off-by: yanghui <yanghui.def@xxxxxxxxxxxxx>
---
mm/mempolicy.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index e32360e90274..e03e0a3cd8d1 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1965,17 +1965,28 @@ 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 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.
+ * Also nodemask should be read from memory atomic especially
+ * MAX_NUMNODES is large enough.
+ */
+ 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;
}
--
2.20.1
