On Mon, Mar 25, 2019 at 06:56:28PM -0700, Bart Van Assche wrote:
> On 3/25/19 6:44 PM, Ming Lei wrote:
> > On Mon, Mar 25, 2019 at 10:01:46AM -0700, Bart Van Assche wrote:
> > > The scsi_end_request() function calls scsi_cmd_to_driver() indirectly
> > > and hence needs the disk->private_data pointer. Avoid that that pointer
> > > is cleared before all affected I/O requests have finished. This patch
> > > avoids that the following crash occurs:
> > >
> > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> > > Call trace:
> > > scsi_mq_uninit_cmd+0x1c/0x30
> > > scsi_end_request+0x7c/0x1b8
> > > scsi_io_completion+0x464/0x668
> > > scsi_finish_command+0xbc/0x160
> > > scsi_eh_flush_done_q+0x10c/0x170
> > > sas_scsi_recover_host+0x84c/0xa98 [libsas]
> > > scsi_error_handler+0x140/0x5b0
> > > kthread+0x100/0x12c
> > > ret_from_fork+0x10/0x18
> > >
> > > Cc: Christoph Hellwig <hch@xxxxxx>
> > > Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> > > Cc: Hannes Reinecke <hare@xxxxxxxx>
> > > Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
> > > Cc: Jason Yan <yanaijie@xxxxxxxxxx>
> > > Cc: <stable@xxxxxxxxxxxxxxx>
> > > Reported-by: Jason Yan <yanaijie@xxxxxxxxxx>
> > > Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> > > ---
> > > drivers/scsi/sd.c | 19 +++++++++++++------
> > > 1 file changed, 13 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> > > index ed34bfbc3844..0077880c0cc8 100644
> > > --- a/drivers/scsi/sd.c
> > > +++ b/drivers/scsi/sd.c
> > > @@ -1416,11 +1416,6 @@ static void sd_release(struct gendisk *disk, fmode_t mode)
> > > scsi_set_medium_removal(sdev, SCSI_REMOVAL_ALLOW);
> > > }
> > > - /*
> > > - * XXX and what if there are packets in flight and this close()
> > > - * XXX is followed by a "rmmod sd_mod"?
> > > - */
> > > -
> > > scsi_disk_put(sdkp);
> > > }
> > > @@ -3483,9 +3478,21 @@ static void scsi_disk_release(struct device *dev)
> > > {
> > > struct scsi_disk *sdkp = to_scsi_disk(dev);
> > > struct gendisk *disk = sdkp->disk;
> > > -
> > > + struct request_queue *q = disk->queue;
> > > +
> > > ida_free(&sd_index_ida, sdkp->index);
> > > + /*
> > > + * Wait until all requests that are in progress have completed.
> > > + * This is necessary to avoid that e.g. scsi_end_request() crashes
> > > + * due to clearing the disk->private_data pointer. Wait from inside
> > > + * scsi_disk_release() instead of from sd_release() to avoid that
> > > + * freezing and unfreezing the request queue affects user space I/O
> > > + * in case multiple processes open a /dev/sd... node concurrently.
> > > + */
> > > + blk_mq_freeze_queue(q);
> > > + blk_mq_unfreeze_queue(q);
> > > +
> > > disk->private_data = NULL;
> > > put_disk(disk);
> > > put_device(&sdkp->device->sdev_gendev);
> >
> > No, this way may cause big performance issue, see my previous comment:
> >
> > https://marc.info/?l=linux-scsi&m=155321977714715&w=2
>
> Have you had a look at this patch? Your comment applies to the previous
> version of this patch. I don't think that it applies to the current version.
OK, sorry for missing that, then this patch looks fine.
It is still a bit over-kill for passthrough IO, but seems not a big
deal.
Thanks,
Ming
