Date:	Tue, 03 Jun 2014 15:45:36 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Joe Lawrence <joe.lawrence@...atus.com>
Cc:	<linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 2/2] block,scsi: convert and handle ERR_PTR from blk_get_request

Joe Lawrence <joe.lawrence@...atus.com> writes:

> The blk_get_request function may fail in low-memory conditions or during
> device removal (even if __GFP_WAIT is set). To distinguish between these
> errors, modify the blk_get_request call stack to return the appropriate
> ERR_PTR. Verify that all callers check the return status and consider
> IS_ERR instead of a simple NULL pointer check.

I'm curious to know what testing you did, and what code paths do
anything different for ENOMEM vs EIO.  I guess ENOMEM may make it all
the way back to userspace?

-Jeff

>
> Signed-off-by: Joe Lawrence <joe.lawrence@...atus.com>
> Acked-by: Jiri Kosina <jkosina@...e.cz> [for pktdvd]
> Acked-by: Boaz Harrosh <bharrosh@...asas.com> [for osd]
> ---
>  block/blk-core.c                            | 34 ++++++++++++++---------------
>  block/bsg.c                                 |  8 +++----
>  block/scsi_ioctl.c                          | 12 +++++-----
>  drivers/block/paride/pd.c                   |  4 ++--
>  drivers/block/pktcdvd.c                     |  4 ++--
>  drivers/block/sx8.c                         |  2 +-
>  drivers/cdrom/cdrom.c                       |  4 ++--
>  drivers/ide/ide-park.c                      |  2 +-
>  drivers/scsi/device_handler/scsi_dh_alua.c  |  2 +-
>  drivers/scsi/device_handler/scsi_dh_emc.c   |  2 +-
>  drivers/scsi/device_handler/scsi_dh_hp_sw.c |  4 ++--
>  drivers/scsi/device_handler/scsi_dh_rdac.c  |  2 +-
>  drivers/scsi/osd/osd_initiator.c            |  4 ++--
>  drivers/scsi/osst.c                         |  2 +-
>  drivers/scsi/scsi_error.c                   |  2 +-
>  drivers/scsi/scsi_lib.c                     |  2 +-
>  drivers/scsi/scsi_tgt_lib.c                 |  2 +-
>  drivers/scsi/sg.c                           |  4 ++--
>  drivers/scsi/st.c                           |  2 +-
>  drivers/target/target_core_pscsi.c          |  2 +-
>  20 files changed, 50 insertions(+), 50 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index a0e3096..cd0e9f3 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -891,9 +891,9 @@ static struct io_context *rq_ioc(struct bio *bio)
>   * Get a free request from @q.  This function may fail under memory
>   * pressure or if @q is dead.
>   *
> - * Must be callled with @q->queue_lock held and,
> - * Returns %NULL on failure, with @q->queue_lock held.
> - * Returns !%NULL on success, with @q->queue_lock *not held*.
> + * Must be called with @q->queue_lock held and,
> + * Returns ERR_PTR on failure, with @q->queue_lock held.
> + * Returns request pointer on success, with @q->queue_lock *not held*.
>   */
>  static struct request *__get_request(struct request_list *rl, int rw_flags,
>  				     struct bio *bio, gfp_t gfp_mask)
> @@ -907,7 +907,7 @@ static struct request *__get_request(struct request_list *rl, int rw_flags,
>  	int may_queue;
>  
>  	if (unlikely(blk_queue_dying(q)))
> -		return NULL;
> +		return ERR_PTR(-ENODEV);
>  
>  	may_queue = elv_may_queue(q, rw_flags);
>  	if (may_queue == ELV_MQUEUE_NO)
> @@ -932,7 +932,7 @@ static struct request *__get_request(struct request_list *rl, int rw_flags,
>  					 * process is not a "batcher", and not
>  					 * exempted by the IO scheduler
>  					 */
> -					return NULL;
> +					return ERR_PTR(-ENOMEM);
>  				}
>  			}
>  		}
> @@ -950,7 +950,7 @@ static struct request *__get_request(struct request_list *rl, int rw_flags,
>  	 * allocated with any setting of ->nr_requests
>  	 */
>  	if (rl->count[is_sync] >= (3 * q->nr_requests / 2))
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	q->nr_rqs[is_sync]++;
>  	rl->count[is_sync]++;
> @@ -1055,7 +1055,7 @@ fail_alloc:
>  rq_starved:
>  	if (unlikely(rl->count[is_sync] == 0))
>  		rl->starved[is_sync] = 1;
> -	return NULL;
> +	return ERR_PTR(-ENOMEM);
>  }
>  
>  /**
> @@ -1068,9 +1068,9 @@ rq_starved:
>   * Get a free request from @q.  If %__GFP_WAIT is set in @gfp_mask, this
>   * function keeps retrying under memory pressure and fails iff @q is dead.
>   *
> - * Must be callled with @q->queue_lock held and,
> - * Returns %NULL on failure, with @q->queue_lock held.
> - * Returns !%NULL on success, with @q->queue_lock *not held*.
> + * Must be called with @q->queue_lock held and,
> + * Returns ERR_PTR on failure, with @q->queue_lock held.
> + * Returns request pointer on success, with @q->queue_lock *not held*.
>   */
>  static struct request *get_request(struct request_queue *q, int rw_flags,
>  				   struct bio *bio, gfp_t gfp_mask)
> @@ -1083,12 +1083,12 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
>  	rl = blk_get_rl(q, bio);	/* transferred to @rq on success */
>  retry:
>  	rq = __get_request(rl, rw_flags, bio, gfp_mask);
> -	if (rq)
> +	if (!IS_ERR(rq))
>  		return rq;
>  
>  	if (!(gfp_mask & __GFP_WAIT) || unlikely(blk_queue_dying(q))) {
>  		blk_put_rl(rl);
> -		return NULL;
> +		return rq;
>  	}
>  
>  	/* wait on @rl and retry */
> @@ -1125,7 +1125,7 @@ static struct request *blk_old_get_request(struct request_queue *q, int rw,
>  
>  	spin_lock_irq(q->queue_lock);
>  	rq = get_request(q, rw, NULL, gfp_mask);
> -	if (!rq)
> +	if (IS_ERR(rq))
>  		spin_unlock_irq(q->queue_lock);
>  	/* q->queue_lock is unlocked at this point */
>  
> @@ -1177,8 +1177,8 @@ struct request *blk_make_request(struct request_queue *q, struct bio *bio,
>  {
>  	struct request *rq = blk_get_request(q, bio_data_dir(bio), gfp_mask);
>  
> -	if (unlikely(!rq))
> -		return ERR_PTR(-ENOMEM);
> +	if (IS_ERR(rq))
> +		return rq;
>  
>  	for_each_bio(bio) {
>  		struct bio *bounce_bio = bio;
> @@ -1559,8 +1559,8 @@ get_rq:
>  	 * Returns with the queue unlocked.
>  	 */
>  	req = get_request(q, rw_flags, bio, GFP_NOIO);
> -	if (unlikely(!req)) {
> -		bio_endio(bio, -ENODEV);	/* @q is dead */
> +	if (IS_ERR(req)) {
> +		bio_endio(bio, PTR_ERR(req));	/* @q is dead */
>  		goto out_unlock;
>  	}
>  
> diff --git a/block/bsg.c b/block/bsg.c
> index 420a5a9..2b1c322 100644
> --- a/block/bsg.c
> +++ b/block/bsg.c
> @@ -271,8 +271,8 @@ bsg_map_hdr(struct bsg_device *bd, struct sg_io_v4 *hdr, fmode_t has_write_perm,
>  	 * map scatter-gather elements separately and string them to request
>  	 */
>  	rq = blk_get_request(q, rw, GFP_KERNEL);
> -	if (!rq)
> -		return ERR_PTR(-ENOMEM);
> +	if (IS_ERR(rq))
> +		return rq;
>  	ret = blk_fill_sgv4_hdr_rq(q, rq, hdr, bd, has_write_perm);
>  	if (ret)
>  		goto out;
> @@ -284,8 +284,8 @@ bsg_map_hdr(struct bsg_device *bd, struct sg_io_v4 *hdr, fmode_t has_write_perm,
>  		}
>  
>  		next_rq = blk_get_request(q, READ, GFP_KERNEL);
> -		if (!next_rq) {
> -			ret = -ENOMEM;
> +		if (IS_ERR(next_rq)) {
> +			ret = PTR_ERR(rq);
>  			goto out;
>  		}
>  		rq->next_rq = next_rq;
> diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
> index e6485c9..f901fb5 100644
> --- a/block/scsi_ioctl.c
> +++ b/block/scsi_ioctl.c
> @@ -313,8 +313,8 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
>  		}
>  
>  	rq = blk_get_request(q, writing ? WRITE : READ, GFP_KERNEL);
> -	if (!rq)
> -		return -ENOMEM;
> +	if (IS_ERR(rq))
> +		return PTR_ERR(rq);
>  
>  	if (blk_fill_sghdr_rq(q, rq, hdr, mode)) {
>  		blk_put_request(rq);
> @@ -442,8 +442,8 @@ int sg_scsi_ioctl(struct request_queue *q, struct gendisk *disk, fmode_t mode,
>  	}
>  
>  	rq = blk_get_request(q, in_len ? WRITE : READ, __GFP_WAIT);
> -	if (!rq) {
> -		err = -ENODEV;
> +	if (IS_ERR(rq)) {
> +		err = PTR_ERR(rq);
>  		goto error_free_buffer;
>  	}
>  
> @@ -533,8 +533,8 @@ static int __blk_send_generic(struct request_queue *q, struct gendisk *bd_disk,
>  	int err;
>  
>  	rq = blk_get_request(q, WRITE, __GFP_WAIT);
> -	if (!rq)
> -		return -ENODEV;
> +	if (IS_ERR(rq))
> +		return PTR_ERR(rq);
>  	rq->cmd_type = REQ_TYPE_BLOCK_PC;
>  	rq->timeout = BLK_DEFAULT_SG_TIMEOUT;
>  	rq->cmd[0] = cmd;
> diff --git a/drivers/block/paride/pd.c b/drivers/block/paride/pd.c
> index 856178a..2af4101 100644
> --- a/drivers/block/paride/pd.c
> +++ b/drivers/block/paride/pd.c
> @@ -722,8 +722,8 @@ static int pd_special_command(struct pd_unit *disk,
>  	int err = 0;
>  
>  	rq = blk_get_request(disk->gd->queue, READ, __GFP_WAIT);
> -	if (!rq)
> -		return -ENODEV;
> +	if (IS_ERR(rq))
> +		return PTR_ERR(rq);
>  
>  	rq->cmd_type = REQ_TYPE_SPECIAL;
>  	rq->special = func;
> diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
> index ff39837..1de6e90 100644
> --- a/drivers/block/pktcdvd.c
> +++ b/drivers/block/pktcdvd.c
> @@ -704,8 +704,8 @@ static int pkt_generic_packet(struct pktcdvd_device *pd, struct packet_command *
>  
>  	rq = blk_get_request(q, (cgc->data_direction == CGC_DATA_WRITE) ?
>  			     WRITE : READ, __GFP_WAIT);
> -	if (!rq)
> -		return -ENODEV;
> +	if (IS_ERR(rq))
> +		return PTR_ERR(rq);
>  
>  	if (cgc->buflen) {
>  		ret = blk_rq_map_kern(q, rq, cgc->buffer, cgc->buflen,
> diff --git a/drivers/block/sx8.c b/drivers/block/sx8.c
> index d5e2d12..5d55285 100644
> --- a/drivers/block/sx8.c
> +++ b/drivers/block/sx8.c
> @@ -568,7 +568,7 @@ static struct carm_request *carm_get_special(struct carm_host *host)
>  		return NULL;
>  
>  	rq = blk_get_request(host->oob_q, WRITE /* bogus */, GFP_KERNEL);
> -	if (!rq) {
> +	if (IS_ERR(rq)) {
>  		spin_lock_irqsave(&host->lock, flags);
>  		carm_put_request(host, crq);
>  		spin_unlock_irqrestore(&host->lock, flags);
> diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
> index 8a3aff7..85e63d3 100644
> --- a/drivers/cdrom/cdrom.c
> +++ b/drivers/cdrom/cdrom.c
> @@ -2161,8 +2161,8 @@ static int cdrom_read_cdda_bpc(struct cdrom_device_info *cdi, __u8 __user *ubuf,
>  		len = nr * CD_FRAMESIZE_RAW;
>  
>  		rq = blk_get_request(q, READ, GFP_KERNEL);
> -		if (!rq) {
> -			ret = -ENOMEM;
> +		if (IS_ERR(rq)) {
> +			ret = PTR_ERR(rq);
>  			break;
>  		}
>  
> diff --git a/drivers/ide/ide-park.c b/drivers/ide/ide-park.c
> index f41558a..ca95860 100644
> --- a/drivers/ide/ide-park.c
> +++ b/drivers/ide/ide-park.c
> @@ -46,7 +46,7 @@ static void issue_park_cmd(ide_drive_t *drive, unsigned long timeout)
>  	 * timeout has expired, so power management will be reenabled.
>  	 */
>  	rq = blk_get_request(q, READ, GFP_NOWAIT);
> -	if (unlikely(!rq))
> +	if (IS_ERR(rq))
>  		goto out;
>  
>  	rq->cmd[0] = REQ_UNPARK_HEADS;
> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
> index 5248c88..5aefcf9 100644
> --- a/drivers/scsi/device_handler/scsi_dh_alua.c
> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c
> @@ -115,7 +115,7 @@ static struct request *get_alua_req(struct scsi_device *sdev,
>  
>  	rq = blk_get_request(q, rw, GFP_NOIO);
>  
> -	if (!rq) {
> +	if (IS_ERR(rq)) {
>  		sdev_printk(KERN_INFO, sdev,
>  			    "%s: blk_get_request failed\n", __func__);
>  		return NULL;
> diff --git a/drivers/scsi/device_handler/scsi_dh_emc.c b/drivers/scsi/device_handler/scsi_dh_emc.c
> index e1c8be0..2ec3261 100644
> --- a/drivers/scsi/device_handler/scsi_dh_emc.c
> +++ b/drivers/scsi/device_handler/scsi_dh_emc.c
> @@ -275,7 +275,7 @@ static struct request *get_req(struct scsi_device *sdev, int cmd,
>  
>  	rq = blk_get_request(sdev->request_queue,
>  			(cmd != INQUIRY) ? WRITE : READ, GFP_NOIO);
> -	if (!rq) {
> +	if (IS_ERR(rq)) {
>  		sdev_printk(KERN_INFO, sdev, "get_req: blk_get_request failed");
>  		return NULL;
>  	}
> diff --git a/drivers/scsi/device_handler/scsi_dh_hp_sw.c b/drivers/scsi/device_handler/scsi_dh_hp_sw.c
> index 084062b..1cf4019 100644
> --- a/drivers/scsi/device_handler/scsi_dh_hp_sw.c
> +++ b/drivers/scsi/device_handler/scsi_dh_hp_sw.c
> @@ -117,7 +117,7 @@ static int hp_sw_tur(struct scsi_device *sdev, struct hp_sw_dh_data *h)
>  
>  retry:
>  	req = blk_get_request(sdev->request_queue, WRITE, GFP_NOIO);
> -	if (!req)
> +	if (IS_ERR(req))
>  		return SCSI_DH_RES_TEMP_UNAVAIL;
>  
>  	req->cmd_type = REQ_TYPE_BLOCK_PC;
> @@ -247,7 +247,7 @@ static int hp_sw_start_stop(struct hp_sw_dh_data *h)
>  	struct request *req;
>  
>  	req = blk_get_request(h->sdev->request_queue, WRITE, GFP_ATOMIC);
> -	if (!req)
> +	if (IS_ERR(req))
>  		return SCSI_DH_RES_TEMP_UNAVAIL;
>  
>  	req->cmd_type = REQ_TYPE_BLOCK_PC;
> diff --git a/drivers/scsi/device_handler/scsi_dh_rdac.c b/drivers/scsi/device_handler/scsi_dh_rdac.c
> index 4b9cf93..5f6e5d8 100644
> --- a/drivers/scsi/device_handler/scsi_dh_rdac.c
> +++ b/drivers/scsi/device_handler/scsi_dh_rdac.c
> @@ -274,7 +274,7 @@ static struct request *get_rdac_req(struct scsi_device *sdev,
>  
>  	rq = blk_get_request(q, rw, GFP_NOIO);
>  
> -	if (!rq) {
> +	if (IS_ERR(rq)) {
>  		sdev_printk(KERN_INFO, sdev,
>  				"get_rdac_req: blk_get_request failed.\n");
>  		return NULL;
> diff --git a/drivers/scsi/osd/osd_initiator.c b/drivers/scsi/osd/osd_initiator.c
> index bac04c2..831f1f9 100644
> --- a/drivers/scsi/osd/osd_initiator.c
> +++ b/drivers/scsi/osd/osd_initiator.c
> @@ -1567,8 +1567,8 @@ static struct request *_make_request(struct request_queue *q, bool has_write,
>  		struct request *req;
>  
>  		req = blk_get_request(q, has_write ? WRITE : READ, flags);
> -		if (unlikely(!req))
> -			return ERR_PTR(-ENOMEM);
> +		if (IS_ERR(req))
> +			return req;
>  
>  		return req;
>  	}
> diff --git a/drivers/scsi/osst.c b/drivers/scsi/osst.c
> index 21883a2..826cda9 100644
> --- a/drivers/scsi/osst.c
> +++ b/drivers/scsi/osst.c
> @@ -362,7 +362,7 @@ static int osst_execute(struct osst_request *SRpnt, const unsigned char *cmd,
>  	int write = (data_direction == DMA_TO_DEVICE);
>  
>  	req = blk_get_request(SRpnt->stp->device->request_queue, write, GFP_KERNEL);
> -	if (!req)
> +	if (IS_ERR(req))
>  		return DRIVER_ERROR << 24;
>  
>  	req->cmd_type = REQ_TYPE_BLOCK_PC;
> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
> index d50531f..ca038ee 100644
> --- a/drivers/scsi/scsi_error.c
> +++ b/drivers/scsi/scsi_error.c
> @@ -1950,7 +1950,7 @@ static void scsi_eh_lock_door(struct scsi_device *sdev)
>  	 * request becomes available
>  	 */
>  	req = blk_get_request(sdev->request_queue, READ, GFP_KERNEL);
> -	if (!req)
> +	if (IS_ERR(req))
>  		return;
>  
>  	req->cmd[0] = ALLOW_MEDIUM_REMOVAL;
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 9db097a..b25fab0b 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -193,7 +193,7 @@ int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
>  	int ret = DRIVER_ERROR << 24;
>  
>  	req = blk_get_request(sdev->request_queue, write, __GFP_WAIT);
> -	if (!req)
> +	if (IS_ERR(req))
>  		return ret;
>  
>  	if (bufflen &&	blk_rq_map_kern(sdev->request_queue, req,
> diff --git a/drivers/scsi/scsi_tgt_lib.c b/drivers/scsi/scsi_tgt_lib.c
> index e51add0..b14c15b 100644
> --- a/drivers/scsi/scsi_tgt_lib.c
> +++ b/drivers/scsi/scsi_tgt_lib.c
> @@ -97,7 +97,7 @@ struct scsi_cmnd *scsi_host_get_command(struct Scsi_Host *shost,
>  	 * we are in target mode we want the opposite.
>  	 */
>  	rq = blk_get_request(shost->uspace_req_q, !write, gfp_mask);
> -	if (!rq)
> +	if (IS_ERR(rq))
>  		goto free_tcmd;
>  
>  	cmd = __scsi_get_command(shost, gfp_mask);
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index df5e961..2e54684 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -1650,8 +1650,8 @@ static int sg_start_req(Sg_request *srp, unsigned char *cmd)
>  				   dxfer_len));
>  
>  	rq = blk_get_request(q, rw, GFP_ATOMIC);
> -	if (!rq)
> -		return -ENOMEM;
> +	if (IS_ERR(rq))
> +		return PTR_ERR(rq);
>  
>  	memcpy(rq->cmd, cmd, hp->cmd_len);
>  
> diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
> index afc834e..48a6cef 100644
> --- a/drivers/scsi/st.c
> +++ b/drivers/scsi/st.c
> @@ -481,7 +481,7 @@ static int st_scsi_execute(struct st_request *SRpnt, const unsigned char *cmd,
>  
>  	req = blk_get_request(SRpnt->stp->device->request_queue, write,
>  			      GFP_KERNEL);
> -	if (!req)
> +	if (IS_ERR(req))
>  		return DRIVER_ERROR << 24;
>  
>  	req->cmd_type = REQ_TYPE_BLOCK_PC;
> diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
> index 0f199f6..23d340d 100644
> --- a/drivers/target/target_core_pscsi.c
> +++ b/drivers/target/target_core_pscsi.c
> @@ -1050,7 +1050,7 @@ pscsi_execute_cmd(struct se_cmd *cmd)
>  		req = blk_get_request(pdv->pdv_sd->request_queue,
>  				(data_direction == DMA_TO_DEVICE),
>  				GFP_KERNEL);
> -		if (!req) {
> +		if (IS_ERR(req)) {
>  			pr_err("PSCSI: blk_get_request() failed\n");
>  			ret = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
>  			goto fail;
--
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