Re: [PATCH v2 13/20] scsi: ufs: Fix a deadlock in the error handler

Bean Huo
2021-11-30T08:55:18Z

Bart,

The concern of this patch is that it reduces the UFS data transmission
queue depth. The cost is a bit high. We are looking for alternative
methods: for example, to fix this problem from the SCSI layer;
Add a new dedicated hardware device management queue on the UFS device
side.

Kind regards,
Bean

On Fri, 2021-11-19 at 11:57 -0800, Bart Van Assche wrote:
> The following deadlock has been observed on a test setup:
> * All tags allocated.
> * The SCSI error handler calls ufshcd_eh_host_reset_handler()
> * ufshcd_eh_host_reset_handler() queues work that calls
> ufshcd_err_handler()
> * ufshcd_err_handler() locks up as follows:
>
> Workqueue: ufs_eh_wq_0 ufshcd_err_handler.cfi_jt
> Call trace:
> __switch_to+0x298/0x5d8
> __schedule+0x6cc/0xa94
> schedule+0x12c/0x298
> blk_mq_get_tag+0x210/0x480
> __blk_mq_alloc_request+0x1c8/0x284
> blk_get_request+0x74/0x134
> ufshcd_exec_dev_cmd+0x68/0x640
> ufshcd_verify_dev_init+0x68/0x35c
> ufshcd_probe_hba+0x12c/0x1cb8
> ufshcd_host_reset_and_restore+0x88/0x254
> ufshcd_reset_and_restore+0xd0/0x354
> ufshcd_err_handler+0x408/0xc58
> process_one_work+0x24c/0x66c
> worker_thread+0x3e8/0xa4c
> kthread+0x150/0x1b4
> ret_from_fork+0x10/0x30
>
> Fix this lockup by making ufshcd_exec_dev_cmd() allocate a reserved
> request.
>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
> drivers/scsi/ufs/ufshcd.c | 17 +++++++----------
> 1 file changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index a241ef6bbc6f..03f4772fc2e2 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -128,8 +128,9 @@ EXPORT_SYMBOL_GPL(ufshcd_dump_regs);
> enum {
> UFSHCD_MAX_CHANNEL = 0,
> UFSHCD_MAX_ID = 1,
> - UFSHCD_CMD_PER_LUN = 32,
> - UFSHCD_CAN_QUEUE = 32,
> + UFSHCD_NUM_RESERVED = 1,
> + UFSHCD_CMD_PER_LUN = 32 - UFSHCD_NUM_RESERVED,
> + UFSHCD_CAN_QUEUE = 32 - UFSHCD_NUM_RESERVED,
> };
>
> static const char *const ufshcd_state_name[] = {
> @@ -2941,12 +2942,7 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba
> *hba,
>
> down_read(&hba->clk_scaling_lock);
>
> - /*
> - * Get free slot, sleep if slots are unavailable.
> - * Even though we use wait_event() which sleeps indefinitely,
> - * the maximum wait time is bounded by SCSI request timeout.
> - */
> - scmd = scsi_get_internal_cmd(q, DMA_TO_DEVICE, 0);
> + scmd = scsi_get_internal_cmd(q, DMA_TO_DEVICE,
> BLK_MQ_REQ_RESERVED);
> if (IS_ERR(scmd)) {
> err = PTR_ERR(scmd);
> goto out_unlock;
> @@ -8171,6 +8167,7 @@ static struct scsi_host_template
> ufshcd_driver_template = {
> .sg_tablesize = SG_ALL,
> .cmd_per_lun = UFSHCD_CMD_PER_LUN,
> .can_queue = UFSHCD_CAN_QUEUE,
> + .reserved_tags = UFSHCD_NUM_RESERVED,
> .max_segment_size = PRDT_DATA_BYTE_COUNT_MAX,
> .max_host_blocked = 1,
> .track_queue_depth = 1,
> @@ -9531,8 +9528,8 @@ int ufshcd_init(struct ufs_hba *hba, void
> __iomem *mmio_base, unsigned int irq)
> /* Configure LRB */
> ufshcd_host_memory_configure(hba);
>
> - host->can_queue = hba->nutrs;
> - host->cmd_per_lun = hba->nutrs;
> + host->can_queue = hba->nutrs - UFSHCD_NUM_RESERVED;
> + host->cmd_per_lun = hba->nutrs - UFSHCD_NUM_RESERVED;
> host->max_id = UFSHCD_MAX_ID;
> host->max_lun = UFS_MAX_LUNS;
> host->max_channel = UFSHCD_MAX_CHANNEL;