From 9ef0a0ffa28edbf5c7cfa6be73b4ecb9896a3875 Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Wed, 6 Aug 2014 16:07:31 -0700 Subject: [PATCH] mm, writeback: prevent race when calculating dirty limits Setting vm_dirty_bytes and dirty_background_bytes is not protected by any serialization. Therefore, it's possible for either variable to change value after the test in global_dirty_limits() to determine whether available_memory needs to be initialized or not. Always ensure that available_memory is properly initialized. Signed-off-by: David Rientjes Acked-by: Johannes Weiner Acked-by: Michal Hocko Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page-writeback.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index e0c943014eb7..91d73ef1744d 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -261,14 +261,11 @@ static unsigned long global_dirtyable_memory(void) */ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) { + const unsigned long available_memory = global_dirtyable_memory(); unsigned long background; unsigned long dirty; - unsigned long uninitialized_var(available_memory); struct task_struct *tsk; - if (!vm_dirty_bytes || !dirty_background_bytes) - available_memory = global_dirtyable_memory(); - if (vm_dirty_bytes) dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); else