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Commit 9ef0a0ff authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds
Browse files

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: default avatarDavid Rientjes <rientjes@google.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 14a4e214

mm/page-writeback.c

+1 −4
Original line number Diff line number Diff line
@@ -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