[PATCH v5 5/6] block: Fix a race between the cgroup code and request queue initialization

Bart Van Assche
2018-02-28T18:15:32Z

Initialize the request queue lock earlier such that the following
race can no longer occur:

blk_init_queue_node() blkcg_print_blkgs()
blk_alloc_queue_node (1)
q->queue_lock = &q->__queue_lock (2)
blkcg_init_queue(q) (3)
spin_lock_irq(blkg->q->queue_lock) (4)
q->queue_lock = lock (5)
spin_unlock_irq(blkg->q->queue_lock) (6)

(1) allocate an uninitialized queue;
(2) initialize queue_lock to its default internal lock;
(3) initialize blkcg part of request queue, which will create blkg and
then insert it to blkg_list;
(4) traverse blkg_list and find the created blkg, and then take its
queue lock, here it is the default *internal lock*;
(5) *race window*, now queue_lock is overridden with *driver specified
lock*;
(6) now unlock *driver specified lock*, not the locked *internal lock*,
unlock balance breaks.

The changes in this patch are as follows:
- Move the .queue_lock initialization from blk_init_queue_node() into
blk_alloc_queue_node().
- Only override the .queue_lock pointer for legacy queues because it
is not useful for blk-mq queues to override this pointer.
- For all all block drivers that initialize .queue_lock explicitly,
change the blk_alloc_queue() call in the driver into a
blk_alloc_queue_node() call and remove the explicit .queue_lock
initialization. Additionally, initialize the spin lock that will
be used as queue lock earlier if necessary.

Reported-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Philipp Reisner <philipp.reisner@linbit.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Kees Cook <keescook@chromium.org>
---
block/blk-core.c | 24 ++++++++++++++++--------
drivers/block/drbd/drbd_main.c | 3 +--
drivers/block/umem.c | 7 +++----
3 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index e873a24bf82d..41c74b37be85 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -888,6 +888,19 @@ static void blk_rq_timed_out_timer(struct timer_list *t)
kblockd_schedule_work(&q->timeout_work);
}

+/**
+ * blk_alloc_queue_node - allocate a request queue
+ * @gfp_mask: memory allocation flags
+ * @node_id: NUMA node to allocate memory from
+ * @lock: For legacy queues, pointer to a spinlock that will be used to e.g.
+ * serialize calls to the legacy .request_fn() callback. Ignored for
+ * blk-mq request queues.
+ *
+ * Note: pass the queue lock as the third argument to this function instead of
+ * setting the queue lock pointer explicitly to avoid triggering a sporadic
+ * crash in the blkcg code. This function namely calls blkcg_init_queue() and
+ * the queue lock pointer must be set before blkcg_init_queue() is called.
+ */
struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id,
spinlock_t *lock)
{
@@ -940,11 +953,8 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id,
mutex_init(&q->sysfs_lock);
spin_lock_init(&q->__queue_lock);

- /*
- * By default initialize queue_lock to internal lock and driver can
- * override it later if need be.
- */
- q->queue_lock = &q->__queue_lock;
+ if (!q->mq_ops)
+ q->queue_lock = lock ? : &q->__queue_lock;

/*
* A queue starts its life with bypass turned on to avoid
@@ -1031,13 +1041,11 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
{
struct request_queue *q;

- q = blk_alloc_queue_node(GFP_KERNEL, node_id, NULL);
+ q = blk_alloc_queue_node(GFP_KERNEL, node_id, lock);
if (!q)
return NULL;

q->request_fn = rfn;
- if (lock)
- q->queue_lock = lock;
if (blk_init_allocated_queue(q) < 0) {
blk_cleanup_queue(q);
return NULL;
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 0a0394aa1b9c..185f1ef00a7c 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2816,7 +2816,7 @@ enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsig

drbd_init_set_defaults(device);

- q = blk_alloc_queue(GFP_KERNEL);
+ q = blk_alloc_queue_node(GFP_KERNEL, NUMA_NO_NODE, &resource->req_lock);
if (!q)
goto out_no_q;
device->rq_queue = q;
@@ -2848,7 +2848,6 @@ enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsig
/* Setting the max_hw_sectors to an odd value of 8kibyte here
This triggers a max_bio_size message upon first attach or connect */
blk_queue_max_hw_sectors(q, DRBD_MAX_BIO_SIZE_SAFE >> 8);
- q->queue_lock = &resource->req_lock;

device->md_io.page = alloc_page(GFP_KERNEL);
if (!device->md_io.page)
diff --git a/drivers/block/umem.c b/drivers/block/umem.c
index 8077123678ad..5c7fb8cc4149 100644
--- a/drivers/block/umem.c
+++ b/drivers/block/umem.c
@@ -888,13 +888,14 @@ static int mm_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
card->Active = -1; /* no page is active */
card->bio = NULL;
card->biotail = &card->bio;
+ spin_lock_init(&card->lock);

- card->queue = blk_alloc_queue(GFP_KERNEL);
+ card->queue = blk_alloc_queue_node(GFP_KERNEL, NUMA_NO_NODE,
+ &card->lock);
if (!card->queue)
goto failed_alloc;

blk_queue_make_request(card->queue, mm_make_request);
- card->queue->queue_lock = &card->lock;
card->queue->queuedata = card;

tasklet_init(&card->tasklet, process_page, (unsigned long)card);
@@ -968,8 +969,6 @@ static int mm_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
dev_printk(KERN_INFO, &card->dev->dev,
"Window size %d bytes, IRQ %d\n", data, dev->irq);

- spin_lock_init(&card->lock);
-
pci_set_drvdata(dev, card);

if (pci_write_cmd != 0x0F) /* If not Memory Write & Invalidate */
--
2.16.2