On 09/03/2013 03:01 PM, Wanpeng Li wrote: > There is a race window between vmap_area free and show vmap_area information. > > A B > > remove_vm_area > spin_lock(&vmap_area_lock); > va->flags &= ~VM_VM_AREA; Here we also do: va->vm = NULL; And see below.... > 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 is introduced by commit: d4033afd(mm, vmalloc: iterate vmap_area_list, > instead of vmlist, in vmallocinfo()). This patch fix it by drop the assumption and > keep not dump vm_map_ram allocation information as the logic before that commit. > > Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx> > --- > mm/vmalloc.c | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 5368b17..62b7932 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2586,13 +2586,6 @@ static int s_show(struct seq_file *m, void *p) > 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); > - return 0; > - } > - > v = va->vm; If we remove the if test above, in the window you said above, va->vm is NULL, but below we will still try to access the members of this vm_struct, which will cause problems... Correct me if I am wrong, please. > > seq_printf(m, "0x%pK-0x%pK %7ld", > -- Thanks. Zhang Yanfei -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>