Commit b997052b authored Aug 13, 2019 by Henry Burns Committed by Linus Torvalds Aug 13, 2019

mm/z3fold.c: fix z3fold_destroy_pool() race condition

The constraint from the zpool use of z3fold_destroy_pool() is there are
no outstanding handles to memory (so no active allocations), but it is
possible for there to be outstanding work on either of the two wqs in
the pool.

Calling z3fold_deregister_migration() before the workqueues are drained
means that there can be allocated pages referencing a freed inode,
causing any thread in compaction to be able to trip over the bad pointer
in PageMovable().

Link: http://lkml.kernel.org/r/20190726224810.79660-2-henryburns@google.com


Fixes: 1f862989 ("mm/z3fold.c: support page migration")
Signed-off-by: Henry Burns <henryburns@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Jonathan Adams <jwadams@google.com>
Cc: Vitaly Vul <vitaly.vul@sony.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Henry Burns <henrywolfeburns@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 6051d3bd

mm/z3fold.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -817,16 +817,19 @@ out:
		static void z3fold_destroy_pool(struct z3fold_pool *pool)
		{
		kmem_cache_destroy(pool->c_handle);
		z3fold_unregister_migration(pool);

		/*
		* We need to destroy pool->compact_wq before pool->release_wq,
		* as any pending work on pool->compact_wq will call
		* queue_work(pool->release_wq, &pool->work).
		*
		* There are still outstanding pages until both workqueues are drained,
		* so we cannot unregister migration until then.
		*/

		destroy_workqueue(pool->compact_wq);
		destroy_workqueue(pool->release_wq);
		z3fold_unregister_migration(pool);
		kfree(pool);
		}

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