Commit 15729ff8 authored by Paolo Valente's avatar Paolo Valente Committed by Jens Axboe
Browse files

Revert "Revert "block, bfq: honor already-setup queue merges"" 

A crash [1] happened to be triggered in conjunction with commit
2d52c58b ("block, bfq: honor already-setup queue merges"). The
latter was then reverted by commit ebc69e89 ("Revert "block, bfq:
honor already-setup queue merges""). Yet, the reverted commit was not
the one introducing the bug. In fact, it actually triggered a UAF
introduced by a different commit, and now fixed by commit d29bd414
("block, bfq: reset last_bfqq_created on group change").

So, there is no point in keeping commit 2d52c58b ("block, bfq:
honor already-setup queue merges") out. This commit restores it.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=214503



Reported-by: default avatarHolger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20211125181510.15004-1-paolo.valente@linaro.org


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 97939610

block/bfq-iosched.c

+13 −3
Original line number Diff line number Diff line
@@ -2782,6 +2782,15 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) 
	 * are likely to increase the throughput.

	 */

	bfqq->new_bfqq = new_bfqq;

	/*

	 * The above assignment schedules the following redirections:

	 * each time some I/O for bfqq arrives, the process that

	 * generated that I/O is disassociated from bfqq and

	 * associated with new_bfqq. Here we increases new_bfqq->ref

	 * in advance, adding the number of processes that are

	 * expected to be associated with new_bfqq as they happen to

	 * issue I/O.

	 */

	new_bfqq->ref += process_refs;

	return new_bfqq;

}
@@ -2844,6 +2853,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, 
{

	struct bfq_queue *in_service_bfqq, *new_bfqq;



	/* if a merge has already been setup, then proceed with that first */

	if (bfqq->new_bfqq)

		return bfqq->new_bfqq;



	/*

	 * Check delayed stable merge for rotational or non-queueing

	 * devs. For this branch to be executed, bfqq must not be
@@ -2945,9 +2958,6 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, 
	if (bfq_too_late_for_merging(bfqq))

		return NULL;



	if (bfqq->new_bfqq)

		return bfqq->new_bfqq;



	if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))

		return NULL;