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
Thanks,
Ming
