[PATCH v16 44/45] sg: add blk_poll support

Douglas Gilbert
2021-02-20T02:07:58Z

The support is added via the new SGV4_FLAG_HIPRI command flag which
causes REQ_HIPRI to be set on the request. Before waiting on an
inflight request, it is checked to see if it has SGV4_FLAG_HIPRI,
and if so blk_poll() is called instead of the wait. In situations
where only the file descriptor is known (e.g. sg_poll() and
ioctl(SG_GET_NUM_WAITING)) all inflight requests associated with
the file descriptor that have SGV4_FLAG_HIPRI set, have blk_poll()
called on them.

It is important to know blk_execute_rq_nowait() has finished before
sending blk_poll() on that request. The SG_RS_INFLIGHT state is set
just before blk_execute_rq_nowait() is called so a new bit setting
SG_FRQ_ISSUED has been added that is set just after that calls
returns.

Note that the implementation of blk_poll() calls mq_poll() in the
LLD associated with the request. Then for any request found to be
ready, blk_poll() invokes the scsi_done() callback. So this means
if blk_poll() returns 1 then sg_rq_end_io() has already been
called for the polled request.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
drivers/scsi/sg.c | 105 +++++++++++++++++++++++++++++++++++++++--
include/uapi/scsi/sg.h | 1 +
2 files changed, 101 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 37258b4804ab..c4a8c189fd87 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -117,12 +117,14 @@ enum sg_rq_state { /* N.B. sg_rq_state_arr assumes SG_RS_AWAIT_RCV==2 */
#define SG_FRQ_BLK_PUT_REQ 8 /* set when blk_put_request() called */
#define SG_FRQ_FOR_MMAP 9 /* request needs PAGE_SIZE elements */
#define SG_FRQ_COUNT_ACTIVE 10 /* sfp->submitted + waiting active */
+#define SG_FRQ_ISSUED 11 /* blk_execute_rq_nowait() finished */

/* Bit positions (flags) for sg_fd::ffd_bm bitmask follow */
#define SG_FFD_FORCE_PACKID 0 /* receive only given pack_id/tag */
#define SG_FFD_CMD_Q 1 /* clear: only 1 active req per fd */
#define SG_FFD_KEEP_ORPHAN 2 /* policy for this fd */
-#define SG_FFD_Q_AT_TAIL 3 /* set: queue reqs at tail of blk q */
+#define SG_FFD_HIPRI_SEEN 3 /* could have HIPRI requests active */
+#define SG_FFD_Q_AT_TAIL 4 /* set: queue reqs at tail of blk q */

/* Bit positions (flags) for sg_device::fdev_bm bitmask follow */
#define SG_FDEV_EXCLUDE 0 /* have fd open with O_EXCL */
@@ -300,6 +302,8 @@ static struct sg_device *sg_get_dev(int min_dev);
static void sg_device_destroy(struct kref *kref);
static struct sg_request *sg_mk_srp_sgat(struct sg_fd *sfp, bool first,
int db_len);
+static int sg_sfp_blk_poll(struct sg_fd *sfp, int loop_count);
+static int sg_srp_blk_poll(struct sg_request *srp, int loop_count);
#if IS_ENABLED(CONFIG_SCSI_LOGGING) && IS_ENABLED(SG_DEBUG)
static const char *sg_rq_st_str(enum sg_rq_state rq_st, bool long_str);
#endif
@@ -1032,8 +1036,11 @@ sg_execute_cmd(struct sg_fd *sfp, struct sg_request *srp)
atomic_inc(&sfp->submitted);
set_bit(SG_FRQ_COUNT_ACTIVE, srp->frq_bm);
}
+ if (srp->rq_flags & SGV4_FLAG_HIPRI)
+ srp->rq->cmd_flags |= REQ_HIPRI;
blk_execute_rq_nowait(sdp->device->request_queue, sdp->disk,
srp->rq, (int)at_head, sg_rq_end_io);
+ set_bit(SG_FRQ_ISSUED, srp->frq_bm);
}

/*
@@ -1704,6 +1711,12 @@ sg_wait_event_srp(struct file *filp, struct sg_fd *sfp, void __user *p,

if (atomic_read(&srp->rq_st) != SG_RS_INFLIGHT)
goto skip_wait; /* and skip _acquire() */
+ if (srp->rq_flags & SGV4_FLAG_HIPRI) {
+ res = sg_srp_blk_poll(srp, -1); /* spin till found */
+ if (unlikely(res < 0))
+ return res;
+ goto skip_wait;
+ }
SG_LOG(3, sfp, "%s: about to wait_event...()\n", __func__);
/* usually will be woken up by sg_rq_end_io() callback */
res = wait_event_interruptible(sfp->read_wait,
@@ -2030,6 +2043,8 @@ sg_ioctl_common(struct file *filp, struct sg_device *sdp, struct sg_fd *sfp,
SG_LOG(3, sfp, "%s: SG_GET_PACK_ID=%d\n", __func__, val);
return put_user(val, ip);
case SG_GET_NUM_WAITING:
+ if (test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+ sg_sfp_blk_poll(sfp, 0); /* LLD may have some ready push */
val = atomic_read(&sfp->waiting);
if (val)
return put_user(val, ip);
@@ -2239,6 +2254,75 @@ sg_compat_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
}
#endif

+static int
+sg_srp_q_blk_poll(struct sg_request *srp, struct request *rqq, struct request_queue *q,
+ int loop_count)
+{
+ int k, n, num;
+ blk_qc_t cookie;
+
+ if (rqq && rqq->mq_hctx)
+ cookie = request_to_qc_t(rqq->mq_hctx, rqq);
+ else
+ return 0;
+ num = (loop_count < 1) ? 1 : loop_count;
+ for (k = 0; k < num; ++k) {
+ if (atomic_read(&srp->rq_st) != SG_RS_INFLIGHT)
+ return 0;
+ n = blk_poll(q, cookie, loop_count < 0 /* spin if negative */);
+ if (n != 0)
+ return n;
+ }
+ return 0;
+}
+
+/*
+ * Check all requests on this sfp that are both inflight and HIPRI. That check involves calling
+ * blk_poll(spin<-false) loop_count times. If loop_count is 0 then call blk_poll once.
+ * If loop_count is negative then call blk_poll(spin<-true)) once for each request.
+ * Returns number found (could be 0) or a negated errno value.
+ */
+static int
+sg_sfp_blk_poll(struct sg_fd *sfp, int loop_count)
+{
+ int res = 0;
+ int n;
+ unsigned long idx, iflags;
+ struct sg_request *srp;
+ struct request *rqq;
+ struct scsi_device *sdev = sfp->parentdp->device;
+ struct request_queue *q = sdev ? sdev->request_queue : NULL;
+ struct xarray *xafp = &sfp->srp_arr;
+
+ if (!q)
+ return -EINVAL;
+ xa_lock_irqsave(xafp, iflags);
+ xa_for_each(xafp, idx, srp) {
+ rqq = srp->rq;
+ if (rqq && (srp->rq_flags & SGV4_FLAG_HIPRI) &&
+ atomic_read(&srp->rq_st) == SG_RS_INFLIGHT &&
+ test_bit(SG_FRQ_ISSUED, srp->frq_bm)) {
+ xa_unlock_irqrestore(xafp, iflags);
+ n = sg_srp_q_blk_poll(srp, rqq, q, loop_count);
+ if (unlikely(n < 0))
+ return n;
+ xa_lock_irqsave(xafp, iflags);
+ res += n;
+ }
+ }
+ xa_unlock_irqrestore(xafp, iflags);
+ return res;
+}
+
+static inline int
+sg_srp_blk_poll(struct sg_request *srp, int loop_count)
+{
+ if (!test_bit(SG_FRQ_ISSUED, srp->frq_bm))
+ return 0; /* blk_execute_rq_nowait() may not have issued request */
+ return sg_srp_q_blk_poll(srp, srp->rq, srp->parentfp->parentdp->device->request_queue,
+ loop_count);
+}
+
/*
* Implements the poll(2) system call for this driver. Returns various EPOLL*
* flags OR-ed together.
@@ -2250,6 +2334,8 @@ sg_poll(struct file *filp, poll_table * wait)
__poll_t p_res = 0;
struct sg_fd *sfp = filp->private_data;

+ if (test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+ sg_sfp_blk_poll(sfp, 0); /* LLD may have some ready to push up */
num = atomic_read(&sfp->waiting);
if (num < 1) {
poll_wait(filp, &sfp->read_wait, wait);
@@ -2561,7 +2647,8 @@ sg_rq_end_io(struct request *rq, blk_status_t status)

if (likely(rqq_state == SG_RS_AWAIT_RCV)) {
/* Wake any sg_read()/ioctl(SG_IORECEIVE) awaiting this req */
- wake_up_interruptible(&sfp->read_wait);
+ if (!(srp->rq_flags & SGV4_FLAG_HIPRI))
+ wake_up_interruptible(&sfp->read_wait);
kill_fasync(&sfp->async_qp, SIGPOLL, POLL_IN);
kref_put(&sfp->f_ref, sg_remove_sfp);
} else { /* clean up orphaned request that aren't being kept */
@@ -3004,6 +3091,8 @@ sg_start_req(struct sg_request *srp, struct sg_comm_wr_t *cwrp, int dxfer_dir)
/* current sg_request protected by SG_RS_BUSY state */
scsi_rp = scsi_req(rq);
srp->rq = rq;
+ if (rq_flags & SGV4_FLAG_HIPRI)
+ set_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm);

if (cwrp->cmd_len > BLK_MAX_CDB)
scsi_rp->cmd = long_cmdp;
@@ -3117,7 +3206,10 @@ sg_finish_scsi_blk_rq(struct sg_request *srp)
SG_LOG(4, sfp, "%s: srp=0x%pK%s\n", __func__, srp,
(srp->parentfp->rsv_srp == srp) ? " rsv" : "");
if (test_and_clear_bit(SG_FRQ_COUNT_ACTIVE, srp->frq_bm)) {
- atomic_dec(&sfp->submitted);
+ bool now_zero = atomic_dec_and_test(&sfp->submitted);
+
+ if (now_zero)
+ clear_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm);
atomic_dec(&sfp->waiting);
}

@@ -3318,6 +3410,8 @@ sg_find_srp_by_id(struct sg_fd *sfp, int pack_id)
struct sg_request *srp = NULL;
struct xarray *xafp = &sfp->srp_arr;

+ if (test_bit(SG_FFD_HIPRI_SEEN, sfp->ffd_bm))
+ sg_sfp_blk_poll(sfp, 0); /* LLD may have some ready to push up */
if (num_waiting < 1) {
num_waiting = atomic_read_acquire(&sfp->waiting);
if (num_waiting < 1)
@@ -4124,8 +4218,9 @@ sg_proc_debug_sreq(struct sg_request *srp, int to, char *obp, int len)
else if (dur < U32_MAX) /* in-flight or busy (so ongoing) */
n += scnprintf(obp + n, len - n, " t_o/elap=%us/%ums",
to / 1000, dur);
- n += scnprintf(obp + n, len - n, " sgat=%d op=0x%02x\n",
- srp->sgat_h.num_sgat, srp->cmd_opcode);
+ cp = (srp->rq_flags & SGV4_FLAG_HIPRI) ? "hipri " : "";
+ n += scnprintf(obp + n, len - n, " sgat=%d %sop=0x%02x\n",
+ srp->sgat_h.num_sgat, cp, srp->cmd_opcode);
return n;
}

diff --git a/include/uapi/scsi/sg.h b/include/uapi/scsi/sg.h
index 6162a5d5995c..11b58b279241 100644
--- a/include/uapi/scsi/sg.h
+++ b/include/uapi/scsi/sg.h
@@ -110,6 +110,7 @@ typedef struct sg_io_hdr {
#define SGV4_FLAG_Q_AT_TAIL SG_FLAG_Q_AT_TAIL
#define SGV4_FLAG_Q_AT_HEAD SG_FLAG_Q_AT_HEAD
#define SGV4_FLAG_IMMED 0x400 /* for polling with SG_IOR, ignored in SG_IOS */
+#define SGV4_FLAG_HIPRI 0x800 /* request will use blk_poll to complete */

/* Output (potentially OR-ed together) in v3::info or v4::info field */
#define SG_INFO_OK_MASK 0x1
--
2.25.1