2013-09-18 00:30:12

by Wanpeng Li

Subject: [PATCH v6 1/2] mm/vmalloc: fix show vmap_area information race with vmap_area tear down

Changelog:
*v4 -> v5: return directly for !VM_VM_AREA case and remove (VM_LAZY_FREE | VM_LAZY_FREEING) check
*v5 -> v6: add KOSAKI's ack

There is a race window between vmap_area tear down and show vmap_area information.

A B

remove_vm_area
spin_lock(&vmap_area_lock);
va->vm = NULL;
va->flags &= ~VM_VM_AREA;
spin_unlock(&vmap_area_lock);
spin_lock(&vmap_area_lock);
if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEZING))
return 0;
if (!(va->flags & VM_VM_AREA)) {
seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
(void *)va->va_start, (void *)va->va_end,
va->va_end - va->va_start);
return 0;
}
free_unmap_vmap_area(va);
flush_cache_vunmap
free_unmap_vmap_area_noflush
unmap_vmap_area
free_vmap_area_noflush
va->flags |= VM_LAZY_FREE

The assumption !VM_VM_AREA represents vm_map_ram allocation is introduced by
commit: d4033afd(mm, vmalloc: iterate vmap_area_list, instead of vmlist, in
vmallocinfo()). However, !VM_VM_AREA also represents vmap_area is being tear
down in race window mentioned above. This patch fix it by don't dump any
information for !VM_VM_AREA case and also remove (VM_LAZY_FREE | VM_LAZY_FREEING)
check since they are not possible for !VM_VM_AREA case.

Suggested-by: Joonsoo Kim <[email protected]>
Acked-by: KOSAKI Motohiro <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
mm/vmalloc.c | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5368b17..9b75028 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2582,16 +2582,13 @@ static int s_show(struct seq_file *m, void *p)
{
struct vmap_area *va = p;
struct vm_struct *v;
-
- if (va->flags & (VM_LAZY_FREE | VM_LAZY_FREEING))
- return 0;
-
- if (!(va->flags & VM_VM_AREA)) {
- seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
- (void *)va->va_start, (void *)va->va_end,
- va->va_end - va->va_start);
+
+ /*
+ * s_show can encounter race with remove_vm_area, !VM_VM_AREA on
+ * behalf of vmap area is being tear down or vm_map_ram allocation.
+ */
+ if (!(va->flags & VM_VM_AREA))
return 0;
- }

v = va->vm;

--
1.8.1.2

2013-09-18 00:30:18

by Wanpeng Li

Subject: [PATCH v6 2/2] mm/vmalloc: drop "caller" argument of __vmalloc_area_node()

__vmalloc_area_node() no longer need "caller" argument. It can use area->caller
instead. This patch drop "caller" argument of __vmalloc_area_node().

Signed-off-by: Wanpeng Li <[email protected]>
---
mm/vmalloc.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d78d117..f75c2aa 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1546,7 +1546,7 @@ static void *__vmalloc_node(unsigned long size, unsigned long align,
gfp_t gfp_mask, pgprot_t prot,
int node, const void *caller);
static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
- pgprot_t prot, int node, const void *caller)
+ pgprot_t prot, int node)
{
const int order = 0;
struct page **pages;
@@ -1560,7 +1560,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
/* Please note that the recursion is strictly bounded. */
if (array_size > PAGE_SIZE) {
pages = __vmalloc_node(array_size, 1, nested_gfp|__GFP_HIGHMEM,
- PAGE_KERNEL, node, caller);
+ PAGE_KERNEL, node, area->caller);
area->flags |= VM_VPAGES;
} else {
pages = kmalloc_node(array_size, nested_gfp, node);
@@ -1633,7 +1633,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
if (!area)
goto fail;

- addr = __vmalloc_area_node(area, gfp_mask, prot, node, caller);
+ addr = __vmalloc_area_node(area, gfp_mask, prot, node);
if (!addr)
goto fail;

--
1.8.1.2