| Message ID | 20210906034658.48721-1-yanghui.def@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [RESEND,v3] mm/mempolicy: fix a race between offset_il_node and mpol_rebind_task | expand |
On Mon, Sep 6, 2021 at 11:47 AM yanghui <yanghui.def@bytedance.com> wrote: > > 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@bytedance.com> LGTM. Reviewed-by: Muchun Song <songmuchun@bytedance.com>
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index e32360e90274..54f6eaff18c5 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1965,17 +1965,26 @@ 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; }
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@bytedance.com> --- Changes in v2: 1.Fix WRITE_ONCE/READ_ONCE can't deal with more than sizeof(long) bits data. Changes in v3: 1.Modify some wrong comments. mm/mempolicy.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-)