Re: [RFC PATCH v2] scsi: fix oops in scsi_uninit_cmd()

[Ming Lei]

On Fri, Mar 22, 2019 at 2:39 AM Bart Van Assche <bvanassche@xxxxxxx> wrote:
>
> On Sat, 2019-03-16 at 10:09 +0800, Jason Yan wrote:
> > If we remove the scsi disk when running io with fio, oops occured with
> > the following condition.
> >
> > [scsi_eh_0]                              [fio]
> > scsi_end_request
> >   ->blk_update_request
> >     ->end_bio(io returned to userspace)
> >                                          close
> >                                            ->sd_release
> >                                               ->scsi_disk_put
> >                                                  ->scsi_disk_release
> >                                                      ->disk->private_data = NULL;
> >
> >   ->scsi_mq_uninit_cmd
> >     ->scsi_uninit_cmd
> >       ->scsi_cmd_to_driver
> >     ->drv is NULL, Oops
> >
> > There is a small window between blk_update_request() and
> > scsi_mq_uninit_cmd() that scsi disk may have been released. This will
> > cause a oops like below:
> >
> > Unable to handle kernel NULL pointer dereference at virtual address
> > 0000000000000000
> > s/sync.c:67, func=xfer, error=In[11347.116050] Mem abort info:
> > put/output error
> > [11347.121598]   ESR = 0x96000006
> > [11347.126200]   Exception class = DABT (current EL), IL = 32 bits
> > [11347.132117]   SET = 0, FnV = 0
> > [11347.135170]   EA = 0, S1PTW = 0
> > [11347.138308] Data abort info:
> > [11347.141186]   ISV = 0, ISS = 0x00000006
> > [11347.145019]   CM = 0, WnR = 0
> > [11347.147977] user pgtable: 4k pages, 48-bit VAs, pgdp =
> > 00000000a67aece2
> > [11347.154591] [0000000000000000] pgd=0000002f90774003,
> > pud=0000002fab098003, pmd=0000000000000000
> > [11347.163304] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> > [11347.168870] Modules linked in: hisi_sas_v3_hw hisi_sas_main libsas
> > [11347.175044] CPU: 56 PID: 4294 Comm: scsi_eh_2 Not tainted
> > 4.19.0-g8052059-dirty #2
> > [11347.182600] Hardware name: Huawei D06/D06, BIOS Hisilicon D06 UEFI
> > RC0 - B601 (V6.01) 11/08/2018
> > [11347.191370] pstate: a0c00009 (NzCv daif ãçÎíã
>
> Please verify whether the following patch is a valid alternative for your patch:
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index ed34bfbc3844..745ffdda1bc1 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -1408,6 +1408,7 @@ static void sd_release(struct gendisk *disk, fmode_t mode)
>  {
>         struct scsi_disk *sdkp = scsi_disk(disk);
>         struct scsi_device *sdev = sdkp->device;
> +       struct request_queue *q = sdkp->disk->queue;
>
>         SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_release\n"));
>
> @@ -1417,9 +1418,12 @@ static void sd_release(struct gendisk *disk, fmode_t mode)
>         }
>
>         /*
> -        * XXX and what if there are packets in flight and this close()
> -        * XXX is followed by a "rmmod sd_mod"?
> +        * Wait until any requests that are in progress have completed.
> +        * This is necessary to avoid that e.g. scsi_end_request() crashes
> +        * due to scsi_disk_relase() clearing the disk->private_data pointer.
>          */
> +       blk_mq_freeze_queue(q);
> +       blk_mq_unfreeze_queue(q);

It is over-kill to drain any requests here, what we want is to just
drain any in-flight
IO requests.

Thanks,
Ming Lei