scsi: core: replace GFP_ATOMIC with GFP_KERNEL in scsi_scan.c

We had a test-report where, under memory pressure, adding LUNs to the
systems would fail (the tests add LUNs strictly in sequence):

[ 5525.853432] scsi 0:0:1:1088045124: Direct-Access     IBM      2107900          .148 PQ: 0 ANSI: 5
[ 5525.853826] scsi 0:0:1:1088045124: alua: supports implicit TPGS
[ 5525.853830] scsi 0:0:1:1088045124: alua: device naa.6005076303ffd32700000000000044da port group 0 rel port 43
[ 5525.853931] sd 0:0:1:1088045124: Attached scsi generic sg10 type 0
[ 5525.854075] sd 0:0:1:1088045124: [sdk] Disabling DIF Type 1 protection
[ 5525.855495] sd 0:0:1:1088045124: [sdk] 2097152 512-byte logical blocks: (1.07 GB/1.00 GiB)
[ 5525.855606] sd 0:0:1:1088045124: [sdk] Write Protect is off
[ 5525.855609] sd 0:0:1:1088045124: [sdk] Mode Sense: ed 00 00 08
[ 5525.855795] sd 0:0:1:1088045124: [sdk] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[ 5525.857838]  sdk: sdk1
[ 5525.859468] sd 0:0:1:1088045124: [sdk] Attached SCSI disk
[ 5525.865073] sd 0:0:1:1088045124: alua: transition timeout set to 60 seconds
[ 5525.865078] sd 0:0:1:1088045124: alua: port group 00 state A preferred supports tolusnA
[ 5526.015070] sd 0:0:1:1088045124: alua: port group 00 state A preferred supports tolusnA
[ 5526.015213] sd 0:0:1:1088045124: alua: port group 00 state A preferred supports tolusnA
[ 5526.587439] scsi_alloc_sdev: Allocation failure during SCSI scanning, some SCSI devices might not be configured
[ 5526.588562] scsi_alloc_sdev: Allocation failure during SCSI scanning, some SCSI devices might not be configured

Looking at the code of scsi_alloc_sdev(), and all the calling contexts,
there seems to be no reason to use GFP_ATMOIC here. All the different
call-contexts use a mutex at some point, and nothing in between that
requires no sleeping, as far as I could see. Additionally, the code that
later allocates the block queue for the device (scsi_mq_alloc_queue())
already uses GFP_KERNEL.

There are similar allocations in two other functions:
scsi_probe_and_add_lun(), and scsi_add_lun(),; that can also be done with
GFP_KERNEL.

Here is the contexts for the three functions so far:

    scsi_alloc_sdev()
        scsi_probe_and_add_lun()
            scsi_sequential_lun_scan()
                __scsi_scan_target()
                    scsi_scan_target()
                        mutex_lock()
                    scsi_scan_channel()
                        scsi_scan_host_selected()
                            mutex_lock()
            scsi_report_lun_scan()
                __scsi_scan_target()
    	            ...
            __scsi_add_device()
                mutex_lock()
            __scsi_scan_target()
                ...
        scsi_report_lun_scan()
            ...
        scsi_get_host_dev()
            mutex_lock()

    scsi_probe_and_add_lun()
        ...

    scsi_add_lun()
        scsi_probe_and_add_lun()
            ...

So replace all these, and give them a bit of a better chance to succeed,
with more chances of reclaim.
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_scan.c

@@ -220,7 +220,7 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
 
 	sdev = kzalloc(sizeof(*sdev) + shost->transportt->device_size,
-		       GFP_ATOMIC);
+		       GFP_KERNEL);
 	if (!sdev)
 		goto out;
 
@@ -788,7 +788,7 @@ static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
 	 */
 	sdev->inquiry = kmemdup(inq_result,
 				max_t(size_t, sdev->inquiry_len, 36),
-				GFP_ATOMIC);
+				GFP_KERNEL);
 	if (sdev->inquiry == NULL)
 		return SCSI_SCAN_NO_RESPONSE;
 
@@ -1079,7 +1079,7 @@ static int scsi_probe_and_add_lun(struct scsi_target *starget,
 	if (!sdev)
 		goto out;
 
-	result = kmalloc(result_len, GFP_ATOMIC |
+	result = kmalloc(result_len, GFP_KERNEL |
 			((shost->unchecked_isa_dma) ? __GFP_DMA : 0));
 	if (!result)
 		goto out_free_sdev;