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[88.147.66.140]) by smtp.gmail.com with ESMTPSA id o7sm83472wmc.36.2019.08.07.07.18.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Aug 2019 07:18:08 -0700 (PDT) From: Paolo Valente To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ulf.hansson@linaro.org, linus.walleij@linaro.org, bfq-iosched@googlegroups.com, oleksandr@natalenko.name, pavel@denx.de, Paolo Valente , Douglas Anderson Subject: [PATCH BUGFIX 2/2] block, bfq: move update of waker and woken list to queue freeing Date: Wed, 7 Aug 2019 16:17:54 +0200 Message-Id: <20190807141754.3567-3-paolo.valente@linaro.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190807141754.3567-1-paolo.valente@linaro.org> References: <20190807141754.3567-1-paolo.valente@linaro.org> MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since commit 13a857a4c4e8 ("block, bfq: detect wakers and unconditionally inject their I/O"), every bfq_queue has a pointer to a waker bfq_queue and a list of the bfq_queues it may wake. In this respect, when a bfq_queue, say Q, remains with no I/O source attached to it, Q cannot be woken by any other bfq_queue, and cannot wake any other bfq_queue. Then Q must be removed from the woken list of its possible waker bfq_queue, and all bfq_queues in the woken list of Q must stop having a waker bfq_queue. Q remains with no I/O source in two cases: when the last process associated with Q exits or when such a process gets associated with a different bfq_queue. Unfortunately, commit 13a857a4c4e8 ("block, bfq: detect wakers and unconditionally inject their I/O") performed the above updates only in the first case. This commit fixes this bug by moving these updates to when Q gets freed. This is a simple and safe way to handle all cases, as both the above events, process exit and re-association, lead to Q being freed soon, and because dangling references would come out only after Q gets freed (if no update were performed). Fixes: 13a857a4c4e8 ("block, bfq: detect wakers and unconditionally inject their I/O") Reported-by: Douglas Anderson Tested-by: Douglas Anderson Signed-off-by: Paolo Valente --- block/bfq-iosched.c | 44 +++++++++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 15 deletions(-) -- 2.20.1 diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index b2009650afc2..5f477501bb3d 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -4765,6 +4765,8 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx) */ void bfq_put_queue(struct bfq_queue *bfqq) { + struct bfq_queue *item; + struct hlist_node *n; #ifdef CONFIG_BFQ_GROUP_IOSCHED struct bfq_group *bfqg = bfqq_group(bfqq); #endif @@ -4809,6 +4811,33 @@ void bfq_put_queue(struct bfq_queue *bfqq) bfqq->bfqd->burst_size--; } + /* + * bfqq does not exist any longer, so it cannot be woken by + * any other queue, and cannot wake any other queue. Then bfqq + * must be removed from the woken list of its possible waker + * queue, and all queues in the woken list of bfqq must stop + * having a waker queue. Strictly speaking, these updates + * should be performed when bfqq remains with no I/O source + * attached to it, which happens before bfqq gets freed. In + * particular, this happens when the last process associated + * with bfqq exits or gets associated with a different + * queue. However, both events lead to bfqq being freed soon, + * and dangling references would come out only after bfqq gets + * freed. So these updates are done here, as a simple and safe + * way to handle all cases. + */ + /* remove bfqq from woken list */ + if (!hlist_unhashed(&bfqq->woken_list_node)) + hlist_del_init(&bfqq->woken_list_node); + + /* reset waker for all queues in woken list */ + hlist_for_each_entry_safe(item, n, &bfqq->woken_list, + woken_list_node) { + item->waker_bfqq = NULL; + bfq_clear_bfqq_has_waker(item); + hlist_del_init(&item->woken_list_node); + } + if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq) bfqq->bfqd->last_completed_rq_bfqq = NULL; @@ -4839,9 +4868,6 @@ static void bfq_put_cooperator(struct bfq_queue *bfqq) static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq) { - struct bfq_queue *item; - struct hlist_node *n; - if (bfqq == bfqd->in_service_queue) { __bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT); bfq_schedule_dispatch(bfqd); @@ -4851,18 +4877,6 @@ static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq) bfq_put_cooperator(bfqq); - /* remove bfqq from woken list */ - if (!hlist_unhashed(&bfqq->woken_list_node)) - hlist_del_init(&bfqq->woken_list_node); - - /* reset waker for all queues in woken list */ - hlist_for_each_entry_safe(item, n, &bfqq->woken_list, - woken_list_node) { - item->waker_bfqq = NULL; - bfq_clear_bfqq_has_waker(item); - hlist_del_init(&item->woken_list_node); - } - bfq_put_queue(bfqq); /* release process reference */ }