From c2ce8c142c43c360047e173d2018d94a4d0f7a59 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Tue, 12 Nov 2013 15:07:31 -0800 Subject: [PATCH] mm/vmalloc: fix show vmap_area information race with vmap_area tear down 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 d4033afdf828 ("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 Acked-by: KOSAKI Motohiro Signed-off-by: Wanpeng Li Cc: Mitsuo Hayasaka Cc: Zhang Yanfei Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmalloc.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 285f0e7d28e7..814ce9122709 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2578,16 +2578,13 @@ 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)) + /* + * 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; - 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; - } - v = va->vm; /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */