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 <rientjes@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index e0c94301..91d73ef 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -261,14 +261,11 @@
*/
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
