Commit 9ef0a0ff authored Aug 06, 2014 by David Rientjes Committed by Linus Torvalds Aug 06, 2014

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>

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

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