Re: [PATCH] mmc: block: Prevent new req entering queue while freeing up the queue

[Adrian Hunter]

On 3/11/20 5:25 pm, Ulf Hansson wrote:
> On Wed, 28 Oct 2020 at 12:20, Veerabhadrarao Badiganti
> <vbadigan@xxxxxxxxxxxxxx> wrote:
>>
>> The commit bbdc74dc19e0 ("mmc: block: Prevent new req entering queue
>> after its cleanup") has introduced this change but it got moved after
>> del_gendisk() with commit 57678e5a3d51 ("mmc: block: Delete gendisk
>> before cleaning up the request queue").
> 
> This isn't the first time we have spotted errors in this path. Seems
> like a difficult path to get correct. :-)
> 
>>
>> It is blocking reboot with below Call stack().
>>
>> INFO: task reboot:3086 blocked for more than 122 seconds.
>>      __schedule
>>      schedule
>>      schedule_timeout
>>      io_schedule_timeout
>>      do_wait_for_common
>>      wait_for_completion_io
>>      submit_bio_wait
>>      blkdev_issue_flush
>>      ext4_sync_fs
>>      __sync_filesystem
>>      sync_filesystem
>>      fsync_bdev
>>      invalidate_partition
>>      del_gendisk
>>      mmc_blk_remove_req
>>      mmc_blk_remove
>>      mmc_bus_remove
>>      device_release_driver_internal
>>      device_release_driver
>>      bus_remove_device
>>      device_del
>>      mmc_remove_card
>>      mmc_remove
>>      mmc_stop_host
>>      mmc_remove_host
>>      sdhci_remove_host
>>      sdhci_msm_remove
> 
> Why do you call sdhci_msm_remove() from the shutdown callback? What
> specific operations do you need to run in the shutdown path for sdhci
> msm?

Yes, the problem is that upper layers, like the mmc block driver, have
already shut down, so doing operations like remove will get into deadlocks.

> 
> The important part should be to do a graceful shutdown of the card
> (and the block device) - is there anything else?
> 
> Or you are just using the shutdown callback as a simple way to trigger
> this problem? Could unbinding the driver trigger the same issue?
> 
>>      sdhci_msm_shutdown
>>      platform_drv_shutdown
>>      device_shutdown
>>      kernel_restart_prepare
>>      kernel_restart
>>
>> So bringing this change back.
>>
>> Signed-off-by: Veerabhadrarao Badiganti <vbadigan@xxxxxxxxxxxxxx>
>> ---
>>
>> I'm observing this issue 100% of the time with shutdown callback added to sdhci-msm driver.
>> I'm trying on 5.4 kernel with ChromeOS.
>>
>> Please let me know if this can be fixed in a better way.
> 
> I don't know yet, but I will have a closer look. Let's also see if
> Adrian has some thoughts.
> 
> Kind regards
> Uffe
> 
>> ---
>>
>>  drivers/mmc/core/block.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
>> index 8d3df0be0355..76dbb2b8a13b 100644
>> --- a/drivers/mmc/core/block.c
>> +++ b/drivers/mmc/core/block.c
>> @@ -2627,6 +2627,7 @@ static void mmc_blk_remove_req(struct mmc_blk_data *md)
>>                  * from being accepted.
>>                  */
>>                 card = md->queue.card;
>> +               blk_set_queue_dying(md->queue.queue);
>>                 if (md->disk->flags & GENHD_FL_UP) {
>>                         device_remove_file(disk_to_dev(md->disk), &md->force_ro);
>>                         if ((md->area_type & MMC_BLK_DATA_AREA_BOOT) &&
>> --
>> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>>