From: Yu Kuai yukuai3@huawei.com

[ Upstream commit a2db328b0839312c169eb42746ec46fc1ab53ed2 ]

Writing 'power' and 'submit_queues' concurrently will trigger kernel panic:

Test script:

modprobe null_blk nr_devices=0 mkdir -p /sys/kernel/config/nullb/nullb0 while true; do echo 1 > submit_queues; echo 4 > submit_queues; done & while true; do echo 1 > power; echo 0 > power; done

Test result:

BUG: kernel NULL pointer dereference, address: 0000000000000148 Oops: 0000 [#1] PREEMPT SMP RIP: 0010:__lock_acquire+0x41d/0x28f0 Call Trace: <TASK> lock_acquire+0x121/0x450 down_write+0x5f/0x1d0 simple_recursive_removal+0x12f/0x5c0 blk_mq_debugfs_unregister_hctxs+0x7c/0x100 blk_mq_update_nr_hw_queues+0x4a3/0x720 nullb_update_nr_hw_queues+0x71/0xf0 [null_blk] nullb_device_submit_queues_store+0x79/0xf0 [null_blk] configfs_write_iter+0x119/0x1e0 vfs_write+0x326/0x730 ksys_write+0x74/0x150

This is because del_gendisk() can concurrent with blk_mq_update_nr_hw_queues():

nullb_device_power_store nullb_apply_submit_queues null_del_dev del_gendisk nullb_update_nr_hw_queues if (!dev->nullb) // still set while gendisk is deleted return 0 blk_mq_update_nr_hw_queues dev->nullb = NULL

Fix this problem by resuing the global mutex to protect nullb_device_power_store() and nullb_update_nr_hw_queues() from configfs.

Fixes: 45919fbfe1c4 ("null_blk: Enable modifying 'submit_queues' after an instance has been configured") Reported-and-tested-by: Yi Zhang yi.zhang@redhat.com Closes: https://lore.kernel.org/all/CAHj4cs9LgsHLnjg8z06LQ3Pr5cax-+Ps+xT7AP7TPnEjStu... Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Zhu Yanjun yanjun.zhu@linux.dev Link: https://lore.kernel.org/r/20240523153934.1937851-1-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Xiangyu Chen xiangyu.chen@windriver.com --- drivers/block/null_blk/main.c | 40 +++++++++++++++++++++++------------ 1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c index f58778b57375..e838eed4aacf 100644 --- a/drivers/block/null_blk/main.c +++ b/drivers/block/null_blk/main.c @@ -392,13 +392,25 @@ static int nullb_update_nr_hw_queues(struct nullb_device *dev, static int nullb_apply_submit_queues(struct nullb_device *dev, unsigned int submit_queues) { - return nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues); + int ret; + + mutex_lock(&lock); + ret = nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues); + mutex_unlock(&lock); + + return ret; }

static int nullb_apply_poll_queues(struct nullb_device *dev, unsigned int poll_queues) { - return nullb_update_nr_hw_queues(dev, dev->submit_queues, poll_queues); + int ret; + + mutex_lock(&lock); + ret = nullb_update_nr_hw_queues(dev, dev->submit_queues, poll_queues); + mutex_unlock(&lock); + + return ret; }

NULLB_DEVICE_ATTR(size, ulong, NULL); @@ -444,28 +456,31 @@ static ssize_t nullb_device_power_store(struct config_item *item, if (ret < 0) return ret;

+ ret = count; + mutex_lock(&lock); if (!dev->power && newp) { if (test_and_set_bit(NULLB_DEV_FL_UP, &dev->flags)) - return count; + goto out; + ret = null_add_dev(dev); if (ret) { clear_bit(NULLB_DEV_FL_UP, &dev->flags); - return ret; + goto out; }

set_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags); dev->power = newp; } else if (dev->power && !newp) { if (test_and_clear_bit(NULLB_DEV_FL_UP, &dev->flags)) { - mutex_lock(&lock); dev->power = newp; null_del_dev(dev->nullb); - mutex_unlock(&lock); } clear_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags); }

- return count; +out: + mutex_unlock(&lock); + return ret; }

CONFIGFS_ATTR(nullb_device_, power); @@ -2102,15 +2117,12 @@ static int null_add_dev(struct nullb_device *dev) blk_queue_flag_set(QUEUE_FLAG_NONROT, nullb->q); blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, nullb->q);

- mutex_lock(&lock); rv = ida_alloc(&nullb_indexes, GFP_KERNEL); - if (rv < 0) { - mutex_unlock(&lock); + if (rv < 0) goto out_cleanup_zone; - } + nullb->index = rv; dev->index = rv; - mutex_unlock(&lock);

blk_queue_logical_block_size(nullb->q, dev->blocksize); blk_queue_physical_block_size(nullb->q, dev->blocksize); @@ -2134,9 +2146,7 @@ static int null_add_dev(struct nullb_device *dev) if (rv) goto out_ida_free;

- mutex_lock(&lock); list_add_tail(&nullb->list, &nullb_list); - mutex_unlock(&lock);

pr_info("disk %s created\n", nullb->disk_name);

@@ -2185,7 +2195,9 @@ static int null_create_dev(void) if (!dev) return -ENOMEM;

+ mutex_lock(&lock); ret = null_add_dev(dev); + mutex_unlock(&lock); if (ret) { null_free_dev(dev); return ret;