From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
vmalloc area runs out in our ARM64 system during an erofs test as
vm_map_ram failed[1]. By following the debug log, we find that
vm_map_ram()->vb_alloc() will allocate new vb->va which corresponding
to 4MB vmalloc area as list_for_each_entry_rcu returns immediately
when vbq->free->next points to vbq->free. That is to say, 65536 times
of page fault after the list's broken will run out of the whole
vmalloc area. This should be introduced by one vbq->free->next point to
vbq->free which makes list_for_each_entry_rcu can not iterate the list
and find the BUG.
[1]
PID: 1 TASK: ffffff80802b4e00 CPU: 6 COMMAND: "init"
#0 [ffffffc08006afe0] __switch_to at ffffffc08111d5cc
#1 [ffffffc08006b040] __schedule at ffffffc08111dde0
#2 [ffffffc08006b0a0] schedule at ffffffc08111e294
#3 [ffffffc08006b0d0] schedule_preempt_disabled at ffffffc08111e3f0
#4 [ffffffc08006b140] __mutex_lock at ffffffc08112068c
#5 [ffffffc08006b180] __mutex_lock_slowpath at ffffffc08111f8f8
#6 [ffffffc08006b1a0] mutex_lock at ffffffc08111f834
#7 [ffffffc08006b1d0] reclaim_and_purge_vmap_areas at ffffffc0803ebc3c
#8 [ffffffc08006b290] alloc_vmap_area at ffffffc0803e83fc
#9 [ffffffc08006b300] vm_map_ram at ffffffc0803e78c0
Fixes: fc1e0d980037 ("mm/vmalloc: prevent stale TLBs in fully utilized blocks")
For detailed reason of broken list, please refer to below URL
https://lore.kernel.org/all/20240531024820.5507-1-hailong.liu@xxxxxxxx/
Suggested-by: Hailong.Liu <hailong.liu@xxxxxxxx>
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
v2: introduce cpu in vmap_block to record the right CPU number
v3: use get_cpu/put_cpu to prevent schedule between core
v4: replace get_cpu/put_cpu by another API to avoid disabling preemption
---
---
mm/vmalloc.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 22aa63f4ef63..89eb034f4ac6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2458,6 +2458,7 @@ struct vmap_block {
struct list_head free_list;
struct rcu_head rcu_head;
struct list_head purge;
+ unsigned int cpu;
};
/* Queue of free and dirty vmap blocks, for allocation and flushing purposes */
@@ -2585,8 +2586,15 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
free_vmap_area(va);
return ERR_PTR(err);
}
-
- vbq = raw_cpu_ptr(&vmap_block_queue);
+ /*
+ * list_add_tail_rcu could happened in another core
+ * rather than vb->cpu due to task migration, which
+ * is safe as list_add_tail_rcu will ensure the list's
+ * integrity together with list_for_each_rcu from read
+ * side.
+ */
+ vb->cpu = raw_smp_processor_id();
+ vbq = per_cpu_ptr(&vmap_block_queue, vb->cpu);
spin_lock(&vbq->lock);
list_add_tail_rcu(&vb->free_list, &vbq->free);
spin_unlock(&vbq->lock);
@@ -2614,9 +2622,10 @@ static void free_vmap_block(struct vmap_block *vb)
}
static bool purge_fragmented_block(struct vmap_block *vb,
- struct vmap_block_queue *vbq, struct list_head *purge_list,
- bool force_purge)
+ struct list_head *purge_list, bool force_purge)
{
+ struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, vb->cpu);
+
if (vb->free + vb->dirty != VMAP_BBMAP_BITS ||
vb->dirty == VMAP_BBMAP_BITS)
return false;
@@ -2664,7 +2673,7 @@ static void purge_fragmented_blocks(int cpu)
continue;
spin_lock(&vb->lock);
- purge_fragmented_block(vb, vbq, &purge, true);
+ purge_fragmented_block(vb, &purge, true);
spin_unlock(&vb->lock);
}
rcu_read_unlock();
@@ -2801,7 +2810,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
* not purgeable, check whether there is dirty
* space to be flushed.
*/
- if (!purge_fragmented_block(vb, vbq, &purge_list, false) &&
+ if (!purge_fragmented_block(vb, &purge_list, false) &&
vb->dirty_max && vb->dirty != VMAP_BBMAP_BITS) {
unsigned long va_start = vb->va->va_start;
unsigned long s, e;
--
2.25.1
