From 02c6dcd543f8f051973ee18bfbc4dc3bd595c558 Mon Sep 17 00:00:00 2001 From: Li Jinlin Date: Tue, 24 Aug 2021 10:59:21 +0800 Subject: scsi: core: Fix hang of freezing queue between blocking and running device We found a hang, the steps to reproduce are as follows: 1. blocking device via scsi_device_set_state() 2. dd if=/dev/sda of=/mnt/t.log bs=1M count=10 3. echo none > /sys/block/sda/queue/scheduler 4. echo "running" >/sys/block/sda/device/state Step 3 and 4 should complete after step 4, but they hang. CPU#0 CPU#1 CPU#2 --------------- ---------------- ---------------- Step 1: blocking device Step 2: dd xxxx ^^^^^^ get request q_usage_counter++ Step 3: switching scheculer elv_iosched_store elevator_switch blk_mq_freeze_queue blk_freeze_queue > blk_freeze_queue_start ^^^^^^ mq_freeze_depth++ > blk_mq_run_hw_queues ^^^^^^ can't run queue when dev blocked > blk_mq_freeze_queue_wait ^^^^^^ Hang here!!! wait q_usage_counter==0 Step 4: running device store_state_field scsi_rescan_device scsi_attach_vpd scsi_vpd_inquiry __scsi_execute blk_get_request blk_mq_alloc_request blk_queue_enter ^^^^^^ Hang here!!! wait mq_freeze_depth==0 blk_mq_run_hw_queues ^^^^^^ dispatch IO, q_usage_counter will reduce to zero blk_mq_unfreeze_queue ^^^^^ mq_freeze_depth-- To fix this, we need to run queue before rescanning device when the device state changes to SDEV_RUNNING. Link: https://lore.kernel.org/r/20210824025921.3277629-1-lijinlin3@huawei.com Fixes: f0f82e2476f6 ("scsi: core: Fix capacity set to zero after offlinining device") Reviewed-by: Bart Van Assche Signed-off-by: Li Jinlin Signed-off-by: Qiu Laibin Signed-off-by: Martin K. Petersen --- drivers/scsi/scsi_sysfs.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index ae9bfc658203..c0d31119d6d7 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -808,12 +808,15 @@ store_state_field(struct device *dev, struct device_attribute *attr, ret = scsi_device_set_state(sdev, state); /* * If the device state changes to SDEV_RUNNING, we need to - * rescan the device to revalidate it, and run the queue to - * avoid I/O hang. + * run the queue to avoid I/O hang, and rescan the device + * to revalidate it. Running the queue first is necessary + * because another thread may be waiting inside + * blk_mq_freeze_queue_wait() and because that call may be + * waiting for pending I/O to finish. */ if (ret == 0 && state == SDEV_RUNNING) { - scsi_rescan_device(dev); blk_mq_run_hw_queues(sdev->request_queue, true); + scsi_rescan_device(dev); } mutex_unlock(&sdev->state_mutex); -- cgit v1.2.3