[PATCHv2] mm: fix incorrect vbq reference in purge_fragmented_block

[zhaoyang.huang]

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")

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
v2: introduce cpu in vmap_block to record the right CPU number
---
---
 mm/vmalloc.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 22aa63f4ef63..ca962b554fa0 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 */
@@ -2574,6 +2575,7 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
 	vb->dirty = 0;
 	vb->dirty_min = VMAP_BBMAP_BITS;
 	vb->dirty_max = 0;
+	vb->cpu = smp_processor_id();
 	bitmap_set(vb->used_map, 0, (1UL << order));
 	INIT_LIST_HEAD(&vb->free_list);
 
@@ -2614,9 +2616,10 @@ 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 +2667,7 @@ 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 +2804,7 @@ 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