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

[Ming Lei]

On Tue, Jun 18, 2019 at 4:57 AM Bart Van Assche <bvanassche@xxxxxxx> 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@xxxxxx>
> > ---
> >   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.

[    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