pool may become suspended during device expansion

When expanding a device zfs needs to rescan the partition table to
get the correct size. This can only happen when we're in the kernel
and requires the device to be closed. As part of the rescan, udev is
notified and the device links are removed and recreated. This leave a
window where the vdev code may try to reopen the device before udev
has recreated the link. If that happens, then the pool may end up in
a suspended state.

To correct this, we leverage the BLKPG_RESIZE_PARTITION ioctl which
allows the partition information to be modified even while it's in use.
This ioctl also does not remove the device link associated with the zfs
data partition so it eliminates the race condition that can occur in
the kernel.

Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Wilson <gwilson@delphix.com>
Closes #10897

lib/libefi/rdwr_efi.c

@@ -44,6 +44,7 @@
 #include <sys/byteorder.h>
 #include <sys/vdev_disk.h>
 #include <linux/fs.h>
+#include <linux/blkpg.h>
 
 static struct uuid_to_ptag {
 	struct uuid	uuid;
@@ -209,19 +210,40 @@ read_disk_info(int fd, diskaddr_t *capacity, uint_t *lbsize)
 	return (0);
 }
 
+/*
+ * Return back the device name associated with the file descriptor. The
+ * caller is responsible for freeing the memory associated with the
+ * returned string.
+ */
+static char *
+efi_get_devname(int fd)
+{
+	char *path;
+	char *dev_name;
+
+	path = calloc(1, PATH_MAX);
+	if (path == NULL)
+		return (NULL);
+
+	/*
+	 * The libefi API only provides the open fd and not the file path.
+	 * To handle this realpath(3) is used to resolve the block device
+	 * name from /proc/self/fd/<fd>.
+	 */
+	(void) sprintf(path, "/proc/self/fd/%d", fd);
+	dev_name = realpath(path, NULL);
+	free(path);
+	return (dev_name);
+}
+
 static int
 efi_get_info(int fd, struct dk_cinfo *dki_info)
 {
-	char *path;
 	char *dev_path;
 	int rval = 0;
 
 	memset(dki_info, 0, sizeof (*dki_info));
 
-	path = calloc(1, PATH_MAX);
-	if (path == NULL)
-		goto error;
-
 	/*
 	 * The simplest way to get the partition number under linux is
 	 * to parse it out of the /dev/<disk><partition> block device name.
@@ -229,16 +251,10 @@ efi_get_info(int fd, struct dk_cinfo *dki_info)
 	 * populates /dev/ so it may be trusted.  The tricky bit here is
 	 * that the naming convention is based on the block device type.
 	 * So we need to take this in to account when parsing out the
-	 * partition information.  Another issue is that the libefi API
-	 * API only provides the open fd and not the file path.  To handle
-	 * this realpath(3) is used to resolve the block device name from
-	 * /proc/self/fd/<fd>.  Aside from the partition number we collect
+	 * partition information.  Aside from the partition number we collect
 	 * some additional device info.
 	 */
-	(void) sprintf(path, "/proc/self/fd/%d", fd);
-	dev_path = realpath(path, NULL);
-	free(path);
-
+	dev_path = efi_get_devname(fd);
 	if (dev_path == NULL)
 		goto error;
 
@@ -1108,6 +1124,35 @@ check_input(struct dk_gpt *vtoc)
 	return (0);
 }
 
+static int
+call_blkpg_ioctl(int fd, int command, diskaddr_t start,
+    diskaddr_t size, uint_t pno)
+{
+	struct blkpg_ioctl_arg ioctl_arg;
+	struct blkpg_partition  linux_part;
+	memset(&linux_part, 0, sizeof (linux_part));
+
+	char *path = efi_get_devname(fd);
+	if (path == NULL) {
+		(void) fprintf(stderr, "failed to retrieve device name\n");
+		return (VT_EINVAL);
+	}
+
+	linux_part.start = start;
+	linux_part.length = size;
+	linux_part.pno = pno;
+	snprintf(linux_part.devname, BLKPG_DEVNAMELTH - 1, "%s%u", path, pno);
+	linux_part.devname[BLKPG_DEVNAMELTH - 1] = '\0';
+	free(path);
+
+	ioctl_arg.op = command;
+	ioctl_arg.flags = 0;
+	ioctl_arg.datalen = sizeof (struct blkpg_partition);
+	ioctl_arg.data = &linux_part;
+
+	return (ioctl(fd, BLKPG, &ioctl_arg));
+}
+
 /*
  * add all the unallocated space to the current label
  */
@@ -1255,19 +1300,73 @@ efi_use_whole_disk(int fd)
 	efi_label->efi_parts[resv_index].p_start += difference;
 	efi_label->efi_last_u_lba = efi_label->efi_last_lba - nblocks;
 
-	rval = efi_write(fd, efi_label);
-	if (rval < 0) {
-		if (efi_debug) {
-			(void) fprintf(stderr,
-			    "efi_use_whole_disk:fail to write label, rval=%d\n",
-			    rval);
-		}
-		efi_free(efi_label);
-		return (rval);
+	/*
+	 * Rescanning the partition table in the kernel can result
+	 * in the device links to be removed (see comment in vdev_disk_open).
+	 * If BLKPG_RESIZE_PARTITION is available, then we can resize
+	 * the partition table online and avoid having to remove the device
+	 * links used by the pool. This provides a very deterministic
+	 * approach to resizing devices and does not require any
+	 * loops waiting for devices to reappear.
+	 */
+#ifdef BLKPG_RESIZE_PARTITION
+	/*
+	 * Delete the reserved partition since we're about to expand
+	 * the data partition and it would overlap with the reserved
+	 * partition.
+	 * NOTE: The starting index for the ioctl is 1 while for the
+	 * EFI partitions it's 0. For that reason we have to add one
+	 * whenever we make an ioctl call.
+	 */
+	rval = call_blkpg_ioctl(fd, BLKPG_DEL_PARTITION, 0, 0, resv_index + 1);
+	if (rval != 0)
+		goto out;
+
+	/*
+	 * Expand the data partition
+	 */
+	rval = call_blkpg_ioctl(fd, BLKPG_RESIZE_PARTITION,
+	    efi_label->efi_parts[data_index].p_start * efi_label->efi_lbasize,
+	    efi_label->efi_parts[data_index].p_size * efi_label->efi_lbasize,
+	    data_index + 1);
+	if (rval != 0) {
+		(void) fprintf(stderr, "Unable to resize data "
+		    "partition:  %d\n", rval);
+		/*
+		 * Since we failed to resize, we need to reset the start
+		 * of the reserve partition and re-create it.
+		 */
+		efi_label->efi_parts[resv_index].p_start -= difference;
 	}
 
+	/*
+	 * Re-add the reserved partition. If we've expanded the data partition
+	 * then we'll move the reserve partition to the end of the data
+	 * partition. Otherwise, we'll recreate the partition in its original
+	 * location. Note that we do this as best-effort and ignore any
+	 * errors that may arise here. This will ensure that we finish writing
+	 * the EFI label.
+	 */
+	(void) call_blkpg_ioctl(fd, BLKPG_ADD_PARTITION,
+	    efi_label->efi_parts[resv_index].p_start * efi_label->efi_lbasize,
+	    efi_label->efi_parts[resv_index].p_size * efi_label->efi_lbasize,
+	    resv_index + 1);
+#endif
+
+	/*
+	 * We're now ready to write the EFI label.
+	 */
+	if (rval == 0) {
+		rval = efi_write(fd, efi_label);
+		if (rval < 0 && efi_debug) {
+			(void) fprintf(stderr, "efi_use_whole_disk:fail "
+			    "to write label, rval=%d\n", rval);
+		}
+	}
+
+out:
 	efi_free(efi_label);
-	return (0);
+	return (rval);
 }
 
 /*

lib/libzfs/os/linux/libzfs_pool_os.c

@@ -72,9 +72,6 @@ zpool_relabel_disk(libzfs_handle_t *hdl, const char *path, const char *msg)
 	 * It's possible that we might encounter an error if the device
 	 * does not have any unallocated space left. If so, we simply
 	 * ignore that error and continue on.
-	 *
-	 * Also, we don't call efi_rescan() - that would just return EBUSY.
-	 * The module will do it for us in vdev_disk_open().
 	 */
 	error = efi_use_whole_disk(fd);
 

module/os/linux/zfs/vdev_disk.c

@@ -34,6 +34,7 @@
 #include <sys/abd.h>
 #include <sys/fs/zfs.h>
 #include <sys/zio.h>
+#include <linux/blkpg.h>
 #include <linux/msdos_fs.h>
 #include <linux/vfs_compat.h>
 
@@ -175,7 +176,8 @@ vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *max_psize,
 
 	/*
 	 * Reopen the device if it is currently open.  When expanding a
-	 * partition force re-scanning the partition table while closed
+	 * partition force re-scanning the partition table if userland
+	 * did not take care of this already. We need to do this while closed
 	 * in order to get an accurate updated block device size.  Then
 	 * since udev may need to recreate the device links increase the
 	 * open retry timeout before reporting the device as unavailable.
@@ -192,6 +194,22 @@ vdev_disk_open(vdev_t *v, uint64_t *psize, uint64_t *max_psize,
 		if (bdev) {
 			if (v->vdev_expanding && bdev != bdev->bd_contains) {
 				bdevname(bdev->bd_contains, disk_name + 5);
+				/*
+				 * If userland has BLKPG_RESIZE_PARTITION,
+				 * then it should have updated the partition
+				 * table already. We can detect this by
+				 * comparing our current physical size
+				 * with that of the device. If they are
+				 * the same, then we must not have
+				 * BLKPG_RESIZE_PARTITION or it failed to
+				 * update the partition table online. We
+				 * fallback to rescanning the partition
+				 * table from the kernel below. However,
+				 * if the capacity already reflects the
+				 * updated partition, then we skip
+				 * rescanning the partition table here.
+				 */
+				if (v->vdev_psize == bdev_capacity(bdev))
 					reread_part = B_TRUE;
 			}