Re: [PATCH 2/8] scsi: take the DMA max mapping size into account

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2019/07/22 15:01, Ming Lei wrote:
> On Tue, Jun 18, 2019 at 4:57 AM Bart Van Assche <bvanassche@acm.org> wrote:
>>
>> On 6/17/19 5:19 AM, Christoph Hellwig wrote:
>>> We need to limit the devices max_sectors to what the DMA mapping
>>> implementation can support.  If not we risk running out of swiotlb
>>> buffers easily.
>>>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>> ---
>>>   drivers/scsi/scsi_lib.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>>> index d333bb6b1c59..f233bfd84cd7 100644
>>> --- a/drivers/scsi/scsi_lib.c
>>> +++ b/drivers/scsi/scsi_lib.c
>>> @@ -1768,6 +1768,8 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
>>>               blk_queue_max_integrity_segments(q, shost->sg_prot_tablesize);
>>>       }
>>>
>>> +     shost->max_sectors = min_t(unsigned int, shost->max_sectors,
>>> +                     dma_max_mapping_size(dev) << SECTOR_SHIFT);
>>>       blk_queue_max_hw_sectors(q, shost->max_sectors);
>>>       if (shost->unchecked_isa_dma)
>>>               blk_queue_bounce_limit(q, BLK_BOUNCE_ISA);
>>
>> Does dma_max_mapping_size() return a value in bytes? Is
>> shost->max_sectors a number of sectors? If so, are you sure that "<<
>> SECTOR_SHIFT" is the proper conversion? Shouldn't that be ">>
>> SECTOR_SHIFT" instead?
> 
> Now the patch has been committed, '<< SECTOR_SHIFT' needs to be fixed.
> 
> Also the following kernel oops is triggered on qemu, and looks
> device->dma_mask is NULL.

Just hit the exact same problem using tcmu-runner (ZBC file handler) on bare
metal (no QEMU). dev->dma_mask is NULL. No problem with real disks though.

> 
> [    5.826483] scsi host0: Virtio SCSI HBA
> [    5.829302] st: Version 20160209, fixed bufsize 32768, s/g segs 256
> [    5.831042] SCSI Media Changer driver v0.25
> [    5.832491] ==================================================================
> [    5.833332] BUG: KASAN: null-ptr-deref in
> dma_direct_max_mapping_size+0x30/0x94
> [    5.833332] Read of size 8 at addr 0000000000000000 by task kworker/u17:0/7
> [    5.835506] nvme nvme0: pci function 0000:00:07.0
> [    5.833332]
> [    5.833332] CPU: 2 PID: 7 Comm: kworker/u17:0 Not tainted 5.3.0-rc1 #1328
> [    5.836999] ahci 0000:00:1f.2: version 3.0
> [    5.833332] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
> BIOS ?-20180724_192412-buildhw-07.phx4
> [    5.833332] Workqueue: events_unbound async_run_entry_fn
> [    5.833332] Call Trace:
> [    5.833332]  dump_stack+0x6f/0x9d
> [    5.833332]  ? dma_direct_max_mapping_size+0x30/0x94
> [    5.833332]  __kasan_report+0x161/0x189
> [    5.833332]  ? dma_direct_max_mapping_size+0x30/0x94
> [    5.833332]  kasan_report+0xe/0x12
> [    5.833332]  dma_direct_max_mapping_size+0x30/0x94
> [    5.833332]  __scsi_init_queue+0xd8/0x1f3
> [    5.833332]  scsi_mq_alloc_queue+0x62/0x89
> [    5.833332]  scsi_alloc_sdev+0x38c/0x479
> [    5.833332]  scsi_probe_and_add_lun+0x22d/0x1093
> [    5.833332]  ? kobject_set_name_vargs+0xa4/0xb2
> [    5.833332]  ? mutex_lock+0x88/0xc4
> [    5.833332]  ? scsi_free_host_dev+0x4a/0x4a
> [    5.833332]  ? _raw_spin_lock_irqsave+0x8c/0xde
> [    5.833332]  ? _raw_write_unlock_irqrestore+0x23/0x23
> [    5.833332]  ? ata_tdev_match+0x22/0x45
> [    5.833332]  ? attribute_container_add_device+0x160/0x17e
> [    5.833332]  ? rpm_resume+0x26a/0x7c0
> [    5.833332]  ? kobject_get+0x12/0x43
> [    5.833332]  ? rpm_put_suppliers+0x7e/0x7e
> [    5.833332]  ? _raw_spin_lock_irqsave+0x8c/0xde
> [    5.833332]  ? _raw_write_unlock_irqrestore+0x23/0x23
> [    5.833332]  ? scsi_target_destroy+0x135/0x135
> [    5.833332]  __scsi_scan_target+0x14b/0x6aa
> [    5.833332]  ? pvclock_clocksource_read+0xc0/0x14e
> [    5.833332]  ? scsi_add_device+0x20/0x20
> [    5.833332]  ? rpm_resume+0x1ae/0x7c0
> [    5.833332]  ? rpm_put_suppliers+0x7e/0x7e
> [    5.833332]  ? _raw_spin_lock_irqsave+0x8c/0xde
> [    5.833332]  ? _raw_write_unlock_irqrestore+0x23/0x23
> [    5.833332]  ? pick_next_task_fair+0x976/0xa3d
> [    5.833332]  ? mutex_lock+0x88/0xc4
> [    5.833332]  scsi_scan_channel+0x76/0x9e
> [    5.833332]  scsi_scan_host_selected+0x131/0x176
> [    5.833332]  ? scsi_scan_host+0x241/0x241
> [    5.833332]  do_scan_async+0x27/0x219
> [    5.833332]  ? scsi_scan_host+0x241/0x241
> [    5.833332]  async_run_entry_fn+0xdc/0x23d
> [    5.833332]  process_one_work+0x327/0x539
> [    5.833332]  worker_thread+0x330/0x492
> [    5.833332]  ? rescuer_thread+0x41f/0x41f
> [    5.833332]  kthread+0x1c6/0x1d5
> [    5.833332]  ? kthread_park+0xd3/0xd3
> [    5.833332]  ret_from_fork+0x1f/0x30
> [    5.833332] ==================================================================
> 
> 
> 
> Thanks,
> Ming Lei
> 


-- 
Damien Le Moal
Western Digital Research