From mboxrd@z Thu Jan 1 00:00:00 1970 From: hare@suse.de (Hannes Reinecke) Date: Tue, 23 Apr 2019 13:19:33 +0200 Subject: [PATCH V6 6/9] blk-mq: always free hctx after request queue is freed In-Reply-To: <20190422033057.GC21375@ming.t460p> References: <20190417034410.31957-1-ming.lei@redhat.com> <20190417034410.31957-7-ming.lei@redhat.com> <63c09210-c20e-6b4a-56fa-b9eac2807cc1@suse.de> <20190417125943.GB5007@ming.t460p> <20190422033057.GC21375@ming.t460p> Message-ID: <9d93cb74-0683-bb42-2545-b4bb2bfbb831@suse.de> On 4/22/19 5:30 AM, Ming Lei wrote: > On Wed, Apr 17, 2019@08:59:43PM +0800, Ming Lei wrote: >> On Wed, Apr 17, 2019@02:08:59PM +0200, Hannes Reinecke wrote: >>> On 4/17/19 5:44 AM, Ming Lei wrote: >>>> In normal queue cleanup path, hctx is released after request queue >>>> is freed, see blk_mq_release(). >>>> >>>> However, in __blk_mq_update_nr_hw_queues(), hctx may be freed because >>>> of hw queues shrinking. This way is easy to cause use-after-free, >>>> because: one implicit rule is that it is safe to call almost all block >>>> layer APIs if the request queue is alive; and one hctx may be retrieved >>>> by one API, then the hctx can be freed by blk_mq_update_nr_hw_queues(); >>>> finally use-after-free is triggered. >>>> >>>> Fixes this issue by always freeing hctx after releasing request queue. >>>> If some hctxs are removed in blk_mq_update_nr_hw_queues(), introduce >>>> a per-queue list to hold them, then try to resuse these hctxs if numa >>>> node is matched. >>>> >>>> Cc: Dongli Zhang >>>> Cc: James Smart >>>> Cc: Bart Van Assche >>>> Cc: linux-scsi at vger.kernel.org, >>>> Cc: Martin K . Petersen , >>>> Cc: Christoph Hellwig , >>>> Cc: James E . J . Bottomley , >>>> Cc: jianchao wang >>>> Signed-off-by: Ming Lei >>>> --- >>>> block/blk-mq.c | 40 +++++++++++++++++++++++++++------------- >>>> include/linux/blk-mq.h | 2 ++ >>>> include/linux/blkdev.h | 7 +++++++ >>>> 3 files changed, 36 insertions(+), 13 deletions(-) >>>> >>>> diff --git a/block/blk-mq.c b/block/blk-mq.c >>>> index eeebba6ec0f7..2ca4395f794d 100644 >>>> --- a/block/blk-mq.c >>>> +++ b/block/blk-mq.c >>>> @@ -2274,6 +2274,10 @@ static void blk_mq_exit_hctx(struct request_queue *q, >>>> set->ops->exit_hctx(hctx, hctx_idx); >>>> blk_mq_remove_cpuhp(hctx); >>>> + >>>> + spin_lock(&q->dead_hctx_lock); >>>> + list_add(&hctx->hctx_list, &q->dead_hctx_list); >>>> + spin_unlock(&q->dead_hctx_lock); >>>> } >>>> static void blk_mq_exit_hw_queues(struct request_queue *q, >>>> @@ -2675,15 +2679,13 @@ static int blk_mq_alloc_ctxs(struct request_queue *q) >>>> */ >>>> void blk_mq_release(struct request_queue *q) >>>> { >>>> - struct blk_mq_hw_ctx *hctx; >>>> - unsigned int i; >>>> + struct blk_mq_hw_ctx *hctx, *next; >>>> cancel_delayed_work_sync(&q->requeue_work); >>>> - /* hctx kobj stays in hctx */ >>>> - queue_for_each_hw_ctx(q, hctx, i) { >>>> - if (!hctx) >>>> - continue; >>>> + /* all hctx are in .dead_hctx_list now */ >>>> + list_for_each_entry_safe(hctx, next, &q->dead_hctx_list, hctx_list) { >>>> + list_del_init(&hctx->hctx_list); >>>> kobject_put(&hctx->kobj); >>>> } >>>> @@ -2750,9 +2752,22 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx( >>>> struct blk_mq_tag_set *set, struct request_queue *q, >>>> int hctx_idx, int node) >>>> { >>>> - struct blk_mq_hw_ctx *hctx; >>>> + struct blk_mq_hw_ctx *hctx = NULL, *tmp; >>>> + >>>> + /* reuse dead hctx first */ >>>> + spin_lock(&q->dead_hctx_lock); >>>> + list_for_each_entry(tmp, &q->dead_hctx_list, hctx_list) { >>>> + if (tmp->numa_node == node) { >>>> + hctx = tmp; >>>> + break; >>>> + } >>>> + } >>>> + if (hctx) >>>> + list_del_init(&hctx->hctx_list); >>>> + spin_unlock(&q->dead_hctx_lock); >>>> - hctx = blk_mq_alloc_hctx(q, set, hctx_idx, node); >>>> + if (!hctx) >>>> + hctx = blk_mq_alloc_hctx(q, set, hctx_idx, node); >>>> if (!hctx) >>>> goto fail; >>>> @@ -2790,10 +2805,8 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, >>>> hctx = blk_mq_alloc_and_init_hctx(set, q, i, node); >>>> if (hctx) { >>>> - if (hctxs[i]) { >>>> + if (hctxs[i]) >>>> blk_mq_exit_hctx(q, set, hctxs[i], i); >>>> - kobject_put(&hctxs[i]->kobj); >>>> - } >>>> hctxs[i] = hctx; >>>> } else { >>>> if (hctxs[i]) >>>> @@ -2824,9 +2837,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, >>>> if (hctx->tags) >>>> blk_mq_free_map_and_requests(set, j); >>>> blk_mq_exit_hctx(q, set, hctx, j); >>>> - kobject_put(&hctx->kobj); >>>> hctxs[j] = NULL; >>>> - >>>> } >>>> } >>>> mutex_unlock(&q->sysfs_lock); >>>> @@ -2869,6 +2880,9 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, >>>> if (!q->queue_hw_ctx) >>>> goto err_sys_init; >>>> + INIT_LIST_HEAD(&q->dead_hctx_list); >>>> + spin_lock_init(&q->dead_hctx_lock); >>>> + >>>> blk_mq_realloc_hw_ctxs(set, q); >>>> if (!q->nr_hw_queues) >>>> goto err_hctxs; >>>> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h >>>> index db29928de467..15d1aa53d96c 100644 >>>> --- a/include/linux/blk-mq.h >>>> +++ b/include/linux/blk-mq.h >>>> @@ -70,6 +70,8 @@ struct blk_mq_hw_ctx { >>>> struct dentry *sched_debugfs_dir; >>>> #endif >>>> + struct list_head hctx_list; >>>> + >>>> /* Must be the last member - see also blk_mq_hw_ctx_size(). */ >>>> struct srcu_struct srcu[0]; >>>> }; >>>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h >>>> index 4b85dc066264..1325f941f0be 100644 >>>> --- a/include/linux/blkdev.h >>>> +++ b/include/linux/blkdev.h >>>> @@ -535,6 +535,13 @@ struct request_queue { >>>> struct mutex sysfs_lock; >>>> + /* >>>> + * for reusing dead hctx instance in case of updating >>>> + * nr_hw_queues >>>> + */ >>>> + struct list_head dead_hctx_list; >>>> + spinlock_t dead_hctx_lock; >>>> + >>>> atomic_t mq_freeze_depth; >>>> #if defined(CONFIG_BLK_DEV_BSG) >>>> >>> Hmm. >>> I don't particularly like this approach. >>> The much saner approach would be to avoid having I/O in-flight in the first >>> place by setting the queue to something else than live, no? >> >> There isn't any in-flight IO since blk_mq_freeze_queue() is returned >> from __blk_mq_update_nr_hw_queues(). >> >> However, there can be reference to hctx in other code paths via >> arbitrary block layer APIs. >> >> Quiesce can't avoid the use-after-free too given RCU read lock may >> not be held in lots of reference to hctx, such as queue_for_each_hw_ctx(). >> >> So this patch might be the simplest approach to fix this issue, IMO. >> >> However, I am open to any solution for this issue. > > Hi Hannes, > > Could you please let us know if you have better idea for this issue? > Otherwise, I think we need to move on since it is real issue, and users > want to fix that. > Okay. Having looked over the problem and possible alternatives, it looks indeed like a viable solution. I do agree that it's a sensible design to have an additional holding area for hardware context elements, given that they might be reassigned during blk_mq_realloc_hw_ctxs(). However, I would rename the 'dead' elements to 'unused' (ie unused_hctx_list etc). And I would deallocate q->queue_hw_ctx in blk_mq_exit_queue() to make things more consistent. Problem with the current patch is that in blk_mq_release() we iterate the 'dead_hctx_list' and free up everything in there, but then blindly call 'kfree(q->queue_hw_ctx)' without checking if there are any context pointers left. When moving the call to blk_mq_exit_queue() we could to a simple WARN_ON(q->queue_hw_ctx) in blk_mq_release() to ensure that everything got deallocated properly. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare at suse.de +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N?rnberg GF: Felix Imend?rffer, Mary Higgins, Sri Rasiah HRB 21284 (AG N?rnberg)