target: Fix PR_APTPL_BUF_LEN buffer size limitation

This patch addresses the original PR_APTPL_BUF_LEN = 8k limitiation
for write-out of PR APTPL metadata that Martin has recently been
running into.

It changes core_scsi3_update_and_write_aptpl() to use vzalloc'ed
memory instead of kzalloc, and increases the default hardcoded
length to 256k.

It also adds logic in core_scsi3_update_and_write_aptpl() to double
the original length upon core_scsi3_update_aptpl_buf() failure, and
retries until the vzalloc'ed buffer is large enough to accommodate
the outgoing APTPL metadata.
Reported-by: Martin Svec <martin.svec@zoner.cz>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_pr.c

@@ -1862,8 +1862,8 @@ static int core_scsi3_update_aptpl_buf(
 		}
 
 		if ((len + strlen(tmp) >= pr_aptpl_buf_len)) {
-			pr_err("Unable to update renaming"
-				" APTPL metadata\n");
+			pr_err("Unable to update renaming APTPL metadata,"
+			       " reallocating larger buffer\n");
 			ret = -EMSGSIZE;
 			goto out;
 		}
@@ -1880,8 +1880,8 @@ static int core_scsi3_update_aptpl_buf(
 			lun->lun_sep->sep_rtpi, lun->unpacked_lun, reg_count);
 
 		if ((len + strlen(tmp) >= pr_aptpl_buf_len)) {
-			pr_err("Unable to update renaming"
-				" APTPL metadata\n");
+			pr_err("Unable to update renaming APTPL metadata,"
+			       " reallocating larger buffer\n");
 			ret = -EMSGSIZE;
 			goto out;
 		}
@@ -1944,7 +1944,7 @@ static int __core_scsi3_write_aptpl_to_file(
 static sense_reason_t core_scsi3_update_and_write_aptpl(struct se_device *dev, bool aptpl)
 {
 	unsigned char *buf;
-	int rc;
+	int rc, len = PR_APTPL_BUF_LEN;
 
 	if (!aptpl) {
 		char *null_buf = "No Registrations or Reservations\n";
@@ -1958,25 +1958,26 @@ static sense_reason_t core_scsi3_update_and_write_aptpl(struct se_device *dev, b
 
 		return 0;
 	}
-
-	buf = kzalloc(PR_APTPL_BUF_LEN, GFP_KERNEL);
+retry:
+	buf = vzalloc(len);
 	if (!buf)
 		return TCM_OUT_OF_RESOURCES;
 
-	rc = core_scsi3_update_aptpl_buf(dev, buf, PR_APTPL_BUF_LEN);
+	rc = core_scsi3_update_aptpl_buf(dev, buf, len);
 	if (rc < 0) {
-		kfree(buf);
-		return TCM_OUT_OF_RESOURCES;
+		vfree(buf);
+		len *= 2;
+		goto retry;
 	}
 
 	rc = __core_scsi3_write_aptpl_to_file(dev, buf);
 	if (rc != 0) {
 		pr_err("SPC-3 PR: Could not update APTPL\n");
-		kfree(buf);
+		vfree(buf);
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 	}
 	dev->t10_pr.pr_aptpl_active = 1;
-	kfree(buf);
+	vfree(buf);
 	pr_debug("SPC-3 PR: Set APTPL Bit Activated\n");
 	return 0;
 }

include/target/target_core_base.h

@@ -409,7 +409,7 @@ struct t10_reservation {
 	/* Activate Persistence across Target Power Loss enabled
 	 * for SCSI device */
 	int pr_aptpl_active;
-#define PR_APTPL_BUF_LEN			8192
+#define PR_APTPL_BUF_LEN			262144
 	u32 pr_generation;
 	spinlock_t registration_lock;
 	spinlock_t aptpl_reg_lock;