Re: [PATCH] mm: fix racing of vb->va when kasan enabled

[Uladzislau Rezki <urezki@gmail.com>]

> On Wed, Jun 22, 2022 at 11:15 AM Zhaoyang Huang <huangzhaoyang@gmail.com> wrote:
> >
> > On Tue, Jun 21, 2022 at 10:29 PM Uladzislau Rezki <urezki@gmail.com> wrote:
> > >
> > > > On Tue, Jun 21, 2022 at 5:27 PM Uladzislau Rezki <urezki@gmail.com> wrote:
> > > > >
> > > > > > On Mon, Jun 20, 2022 at 6:44 PM Uladzislau Rezki <urezki@gmail.com> wrote:
> > > > > > >
> > > > > > > > > >
> > > > > > > > > Is it easy to reproduce? If so could you please describe the steps? As i see
> > > > > > > > > the freeing of the "vb" is RCU safe whereas vb->va is not. But from the first
> > > > > > > > > glance i do not see how it can accessed twice. Hm..
> > > > > > > > It was raised from a monkey test on A13_k515 system and got 1/20 pcs
> > > > > > > > failed. IMO, vb->va which out of vmap_purge_lock protection could race
> > > > > > > > with a concurrent ra freeing within __purge_vmap_area_lazy.
> > > > > > > >
> > > > > > > Do you have exact steps how you run "monkey" test?
> > > > > > There are about 30+ kos inserted during startup which could be a
> > > > > > specific criteria for reproduction. Do you have doubts about the test
> > > > > > result or the solution?
> > > > > > >
> > > > > I do not have any doubt about your test results, so if you can trigger it
> > > > > then there is an issue at least on the 5.4.161-android12 kernel.
> > > > >
> > > > > 1. With your fix we get expanded mutex range, thus the worst case of vmalloc
> > > > > allocation can be increased when it fails and repeat. Because it also invokes
> > > > > the purge_vmap_area_lazy() that access the same mutex.
> > > > I am not sure I get your point. _vm_unmap_aliases calls
> > > > _purge_vmap_area_lazy instead of purge_vmap_area_lazy. Do you have any
> > > > other solutions? I really don't think my patch is the best way as I
> > > > don't have a full view of vmalloc mechanism.
> > > >
> > > Yep, but it holds the mutex:
> I still don't get how _purge_vmap_area_lazy hold vmap_purge_lock?
>
The user has to take the mutex if it invokes the __purge_vmap_area_lazy()
function.

> > >
> > > <snip>
> > > mutex_lock(&vmap_purge_lock);
> > > purge_fragmented_blocks_allcpus();
> > > if (!__purge_vmap_area_lazy(start, end) && flush)
> > >         flush_tlb_kernel_range(start, end);
> > > mutex_unlock(&vmap_purge_lock);
> > > <snip>
> > >
> > > I do not have a solution yet. I am trying still to figure out how you can
> > > trigger it.
> > >
> > > <snip>
> > >         rcu_read_lock();
> > >         list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> > >                 spin_lock(&vb->lock);
> > >                 if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
> > >                         unsigned long va_start = vb->va->va_start;
> > > <snip>
> > >
> > > so you say that "vb->va->va_start" can be accessed twice. I do not see
> > > how it can happen. The purge_fragmented_blocks() removes "vb" from the
> > > free_list and set vb->dirty to the VMAP_BBMAP_BITS to prevent purging
> > > it again. It is protected by the spin_lock(&vb->lock):
> > >
> > > <snip>
> > > spin_lock(&vb->lock);
> > > if (vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS) {
> > >         vb->free = 0; /* prevent further allocs after releasing lock */
> > >         vb->dirty = VMAP_BBMAP_BITS; /* prevent purging it again */
> > >         vb->dirty_min = 0;
> > >         vb->dirty_max = VMAP_BBMAP_BITS;
> > > <snip>
> > >
> > > so the VMAP_BBMAP_BITS is set under spinlock. The _vm_unmap_aliases() checks it:
> > >
> > > <snip>
> > > list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> > >         spin_lock(&vb->lock);
> > >         if (vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
> > >                 unsigned long va_start = vb->va->va_start;
> > >                 unsigned long s, e;
> > > <snip>
> > >
> > > if the "vb->dirty != VMAP_BBMAP_BITS". I am missing your point here?
> > Could the racing be like bellowing scenario?  vb->va accessed in [2]
> > has been freed in [1]
> >
> > _vm_unmap_aliases
> >                 _vm_unmap_aliases
> > {
> >                                {
> >               list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> >              __purge_vmap_area_lazy
> >                      spin_lock(&vb->lock);
> >                                 merge_or_add_vmap_area
> >                      if (vb->dirty) {
> >
> > kmem_cache_free(vmap_area_cachep, va)[1]
> >                             unsigned long va_start = vb->va->va_start;
> > [2]
> 
> reformat the racing graph
>  _vm_unmap_aliases
>                              _vm_unmap_aliases
>  {
>                                               {
>             list_for_each_entry_rcu(vb, &vbq->free, free_list) {
>                    __purge_vmap_area_lazy
>                       spin_lock(&vb->lock);
>                                         merge_or_add_vmap_area
>                       if (vb->dirty) {
> 
> kmem_cache_free(vmap_area_cachep, va)[1]
>                              unsigned long va_start = vb->va->va_start; [2]
> 
> > >
> > > > >
> > > > > 2. You run 5.4.161-android12 kernel what is quite old. Could you please
> > > > > retest with latest kernel? I am asking because on the latest kernel with
> > > > > CONFIG_KASAN i am not able to reproduce it.
> > > > >
> > > > > I do a lot of: vm_map_ram()/vm_unmap_ram()/vmalloc()/vfree() in parallel
> > > > > by 64 kthreads on my 64 CPUs test system.
> > > > The failure generates at 20s from starting up, I think it is a rare timing.
> > > > >
> > > > > Could you please confirm that you can trigger an issue on the latest kernel?
> > > > Sorry, I don't have an available latest kernel for now.
> > > >
> > > Can you do: "gdb ./vmlinux", execute "l *_vm_unmap_aliases+0x164" and provide
> > > output?
> Sorry, I have lost the vmlinux with KASAN enabled and just got some
> instructions from logs.
>
> 0xffffffd010678da8 <_vm_unmap_aliases+0x134>: sub x22, x26, #0x28
>                x26 vbq->free
> 0xffffffd010678dac <_vm_unmap_aliases+0x138>: lsr x8, x22, #3
> 0xffffffd010678db0 <_vm_unmap_aliases+0x13c>: ldrb w8, [x8,x24]
> 0xffffffd010678db4 <_vm_unmap_aliases+0x140>: cbz w8,
> 0xffffffd010678dc0 <_vm_unmap_aliases+0x14c>
> 0xffffffd010678db8 <_vm_unmap_aliases+0x144>: mov x0, x22
> 0xffffffd010678dbc <_vm_unmap_aliases+0x148>: bl 0xffffffd0106c9a34
> <__asan_report_load8_noabort>
> 0xffffffd010678dc0 <_vm_unmap_aliases+0x14c>: ldr x22, [x22]
> 0xffffffd010678dc4 <_vm_unmap_aliases+0x150>: lsr x8, x22, #3
> 0xffffffd010678dc8 <_vm_unmap_aliases+0x154>: ldrb w8, [x8,x24]
> 0xffffffd010678dcc <_vm_unmap_aliases+0x158>: cbz w8,
> 0xffffffd010678dd8 <_vm_unmap_aliases+0x164>
> 0xffffffd010678dd0 <_vm_unmap_aliases+0x15c>: mov x0, x22
> 0xffffffd010678dd4 <_vm_unmap_aliases+0x160>: bl 0xffffffd0106c9a34
> <__asan_report_load8_noabort>
>
Could you please test below patch if that fixes an issue on the 5.4
kernel:

<snip>
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 4e7809408073..d5b07d7239bd 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -55,6 +55,7 @@ struct vmap_area {
 
 	struct rb_node rb_node;         /* address sorted rbtree */
 	struct list_head list;          /* address sorted list */
+	struct rcu_head rcu;
 
 	/*
 	 * The following three variables can be packed, because
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a3c70e275f4e..bb8cfdb06ce6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -337,14 +337,6 @@ static LLIST_HEAD(vmap_purge_list);
 static struct rb_root vmap_area_root = RB_ROOT;
 static bool vmap_initialized __read_mostly;
 
-/*
- * This kmem_cache is used for vmap_area objects. Instead of
- * allocating from slab we reuse an object from this cache to
- * make things faster. Especially in "no edge" splitting of
- * free block.
- */
-static struct kmem_cache *vmap_area_cachep;
-
 /*
  * This linked list is used in pair with free_vmap_area_root.
  * It gives O(1) access to prev/next to perform fast coalescing.
@@ -532,7 +524,7 @@ link_va(struct vmap_area *va, struct rb_root *root,
 	}
 
 	/* Address-sort this list */
-	list_add(&va->list, head);
+	list_add_rcu(&va->list, head);
 }
 
 static __always_inline void
@@ -547,7 +539,7 @@ unlink_va(struct vmap_area *va, struct rb_root *root)
 	else
 		rb_erase(&va->rb_node, root);
 
-	list_del(&va->list);
+	list_del_rcu(&va->list);
 	RB_CLEAR_NODE(&va->rb_node);
 }
 
@@ -721,7 +713,7 @@ merge_or_add_vmap_area(struct vmap_area *va,
 			augment_tree_propagate_from(sibling);
 
 			/* Free vmap_area object. */
-			kmem_cache_free(vmap_area_cachep, va);
+			kfree_rcu(va, rcu);
 
 			/* Point to the new merged area. */
 			va = sibling;
@@ -748,7 +740,7 @@ merge_or_add_vmap_area(struct vmap_area *va,
 				unlink_va(va, root);
 
 			/* Free vmap_area object. */
-			kmem_cache_free(vmap_area_cachep, va);
+			kfree_rcu(va, rcu);
 			return;
 		}
 	}
@@ -928,7 +920,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
 		 * |---------------|
 		 */
 		unlink_va(va, &free_vmap_area_root);
-		kmem_cache_free(vmap_area_cachep, va);
+		kfree_rcu(va, rcu);
 	} else if (type == LE_FIT_TYPE) {
 		/*
 		 * Split left edge of fit VA.
@@ -969,7 +961,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
 			 * a first allocation (early boot up) when we have "one"
 			 * big free space that has to be split.
 			 */
-			lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT);
+			lva = kmalloc(sizeof(struct vmap_area), GFP_NOWAIT);
 			if (!lva)
 				return -1;
 		}
@@ -1064,8 +1056,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 
 	might_sleep();
 
-	va = kmem_cache_alloc_node(vmap_area_cachep,
-			gfp_mask & GFP_RECLAIM_MASK, node);
+	va = kmalloc_node(sizeof(struct vmap_area), gfp_mask & GFP_RECLAIM_MASK, node);
 	if (unlikely(!va))
 		return ERR_PTR(-ENOMEM);
 
@@ -1091,12 +1082,12 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 	preempt_disable();
 	if (!__this_cpu_read(ne_fit_preload_node)) {
 		preempt_enable();
-		pva = kmem_cache_alloc_node(vmap_area_cachep, GFP_KERNEL, node);
+		pva = kmalloc_node(sizeof(struct vmap_area), GFP_KERNEL, node);
 		preempt_disable();
 
 		if (__this_cpu_cmpxchg(ne_fit_preload_node, NULL, pva)) {
 			if (pva)
-				kmem_cache_free(vmap_area_cachep, pva);
+				kfree_rcu(pva, rcu);
 		}
 	}
 
@@ -1145,7 +1136,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 		pr_warn("vmap allocation for size %lu failed: use vmalloc=<size> to increase size\n",
 			size);
 
-	kmem_cache_free(vmap_area_cachep, va);
+	kfree_rcu(va, rcu);
 	return ERR_PTR(-EBUSY);
 }
 
@@ -1870,7 +1861,7 @@ static void vmap_init_free_space(void)
 	 */
 	list_for_each_entry(busy, &vmap_area_list, list) {
 		if (busy->va_start - vmap_start > 0) {
-			free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
+			free = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
 			if (!WARN_ON_ONCE(!free)) {
 				free->va_start = vmap_start;
 				free->va_end = busy->va_start;
@@ -1885,7 +1876,7 @@ static void vmap_init_free_space(void)
 	}
 
 	if (vmap_end - vmap_start > 0) {
-		free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
+		free = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
 		if (!WARN_ON_ONCE(!free)) {
 			free->va_start = vmap_start;
 			free->va_end = vmap_end;
@@ -1903,11 +1894,6 @@ void __init vmalloc_init(void)
 	struct vm_struct *tmp;
 	int i;
 
-	/*
-	 * Create the cache for vmap_area objects.
-	 */
-	vmap_area_cachep = KMEM_CACHE(vmap_area, SLAB_PANIC);
-
 	for_each_possible_cpu(i) {
 		struct vmap_block_queue *vbq;
 		struct vfree_deferred *p;
@@ -1922,7 +1908,7 @@ void __init vmalloc_init(void)
 
 	/* Import existing vmlist entries. */
 	for (tmp = vmlist; tmp; tmp = tmp->next) {
-		va = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
+		va = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT);
 		if (WARN_ON_ONCE(!va))
 			continue;
 
@@ -3256,7 +3242,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 		goto err_free2;
 
 	for (area = 0; area < nr_vms; area++) {
-		vas[area] = kmem_cache_zalloc(vmap_area_cachep, GFP_KERNEL);
+		vas[area] = kzalloc(sizeof(struct vmap_area), GFP_KERNEL);
 		vms[area] = kzalloc(sizeof(struct vm_struct), GFP_KERNEL);
 		if (!vas[area] || !vms[area])
 			goto err_free;
@@ -3376,8 +3362,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 			if (vas[area])
 				continue;
 
-			vas[area] = kmem_cache_zalloc(
-				vmap_area_cachep, GFP_KERNEL);
+			vas[area] = kzalloc(sizeof(struct vmap_area), GFP_KERNEL);
 			if (!vas[area])
 				goto err_free;
 		}
@@ -3388,7 +3373,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 err_free:
 	for (area = 0; area < nr_vms; area++) {
 		if (vas[area])
-			kmem_cache_free(vmap_area_cachep, vas[area]);
+			kfree_rcu(vas[area], rcu);
 
 		kfree(vms[area]);
 	}
<snip>


--
Uladzislau Rezki