linux-kernel - [PATCH BUGFIX/IMPROVEMENT V2 5/6] block, bfq: keep shared queues out of the waker mechanism

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210304174627.161-6-paolo.valente@linaro.org>
Date:   Thu,  4 Mar 2021 18:46:26 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Valente <paolo.valente@...aro.org>,
        Jan Kara <jack@...e.cz>
Subject: [PATCH BUGFIX/IMPROVEMENT V2 5/6] block, bfq: keep shared queues out of the waker mechanism

Shared queues are likely to receive I/O at a high rate. This may
deceptively let them be considered as wakers of other queues. But a
false waker will unjustly steal bandwidth to its supposedly woken
queue. So considering also shared queues in the waking mechanism may
cause more control troubles than throughput benefits. This commit
keeps shared queues out of the waker-detection mechanism.

Tested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
---
 block/bfq-iosched.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 8497d0803d74..c62dbbe9cc33 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5852,7 +5852,17 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
 			1UL<<(BFQ_RATE_SHIFT - 10))
 		bfq_update_rate_reset(bfqd, NULL);
 	bfqd->last_completion = now_ns;
-	bfqd->last_completed_rq_bfqq = bfqq;
+	/*
+	 * Shared queues are likely to receive I/O at a high
+	 * rate. This may deceptively let them be considered as wakers
+	 * of other queues. But a false waker will unjustly steal
+	 * bandwidth to its supposedly woken queue. So considering
+	 * also shared queues in the waking mechanism may cause more
+	 * control troubles than throughput benefits. Then do not set
+	 * last_completed_rq_bfqq to bfqq if bfqq is a shared queue.
+	 */
+	if (!bfq_bfqq_coop(bfqq))
+		bfqd->last_completed_rq_bfqq = bfqq;
 
 	/*
 	 * If we are waiting to discover whether the request pattern
-- 
2.20.1