[PATCH] IB/srp: Process REQ_PREEMPT requests correctly

[Bart Van Assche <bart.vanassche@sandisk.com>]

Delay REQ_PREEMPT requests submitted against a blocked device
until the device is unblocked by returning SCSI_MLQUEUE_HOST_BUSY
to the SCSI mid-layer. This avoids that a rescan shortly after a
cable pull sporadically triggers the following kernel oops:

BUG: unable to handle kernel paging request at ffffc9001a6bc084
IP: [<ffffffffa04e08f2>] mlx4_ib_post_send+0xd2/0xb30 [mlx4_ib]
Process rescan-scsi-bus (pid: 9241, threadinfo ffff88053484a000, task ffff880534aae100)
Call Trace:
 [<ffffffffa0718135>] srp_post_send+0x65/0x70 [ib_srp]
 [<ffffffffa071b9df>] srp_queuecommand+0x1cf/0x3e0 [ib_srp]
 [<ffffffffa0001ff1>] scsi_dispatch_cmd+0x101/0x280 [scsi_mod]
 [<ffffffffa0009ad1>] scsi_request_fn+0x411/0x4d0 [scsi_mod]
 [<ffffffff81223b37>] __blk_run_queue+0x27/0x30
 [<ffffffff8122a8d2>] blk_execute_rq_nowait+0x82/0x110
 [<ffffffff8122a9c2>] blk_execute_rq+0x62/0xf0
 [<ffffffffa000b0e8>] scsi_execute+0xe8/0x190 [scsi_mod]
 [<ffffffffa000b2f3>] scsi_execute_req+0xa3/0x130 [scsi_mod]
 [<ffffffffa000c1aa>] scsi_probe_lun+0x17a/0x450 [scsi_mod]
 [<ffffffffa000ce86>] scsi_probe_and_add_lun+0x156/0x480 [scsi_mod]
 [<ffffffffa000dc2f>] __scsi_scan_target+0xdf/0x1f0 [scsi_mod]
 [<ffffffffa000dfa3>] scsi_scan_host_selected+0x183/0x1c0 [scsi_mod]
 [<ffffffffa000edfb>] scsi_scan+0xdb/0xe0 [scsi_mod]
 [<ffffffffa000ee13>] store_scan+0x13/0x20 [scsi_mod]
 [<ffffffff811c8d9b>] sysfs_write_file+0xcb/0x160
 [<ffffffff811589de>] vfs_write+0xce/0x140
 [<ffffffff81158b53>] sys_write+0x53/0xa0
 [<ffffffff81464592>] system_call_fastpath+0x16/0x1b
 [<00007f611c9d9300>] 0x7f611c9d92ff

Reported-by: Max Gurtuvoy <maxg@mellanox.com>
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: <stable@vger.kernel.org>
---
 drivers/infiniband/ulp/srp/ib_srp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index 0747c05..77a7a2f 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -2003,8 +2003,13 @@ static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
 	if (in_scsi_eh)
 		mutex_lock(&rport->mutex);
 
+	/*
+	 * The "blocked" state of SCSI devices is ignored by the SCSI core for
+	 * REQ_PREEMPT requests. Hence the explicit check below for the SCSI
+	 * device state.
+	 */
 	scmnd->result = srp_chkready(target->rport);
-	if (unlikely(scmnd->result))
+	if (unlikely(scmnd->result != 0 || scsi_device_blocked(scmnd->device)))
 		goto err;
 
 	WARN_ON_ONCE(scmnd->request->tag < 0);
-- 
2.1.4