scsi: sr: Avoid that opening a CD-ROM hangs with runtime power management enabled

Surround scsi_execute() calls with scsi_autopm_get_device() and
scsi_autopm_put_device(). Note: removing sr_mutex protection from the
scsi_cd_get() and scsi_cd_put() calls is safe because the purpose of
sr_mutex is to serialize cdrom_*() calls.

This patch avoids that complaints similar to the following appear in the
kernel log if runtime power management is enabled:

INFO: task systemd-udevd:650 blocked for more than 120 seconds.
Not tainted 4.18.0-rc7-dbg+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
systemd-udevd D28176 650 513 0x00000104
Call Trace:
__schedule+0x444/0xfe0
schedule+0x4e/0xe0
schedule_preempt_disabled+0x18/0x30
__mutex_lock+0x41c/0xc70
mutex_lock_nested+0x1b/0x20
__blkdev_get+0x106/0x970
blkdev_get+0x22c/0x5a0
blkdev_open+0xe9/0x100
do_dentry_open.isra.19+0x33e/0x570
vfs_open+0x7c/0xd0
path_openat+0x6e3/0x1120
do_filp_open+0x11c/0x1c0
do_sys_open+0x208/0x2d0
__x64_sys_openat+0x59/0x70
do_syscall_64+0x77/0x230
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Signed-off-by: Bart Van Assche <[e-mail]>
Cc: Maurizio Lombardi <[e-mail]>
Cc: Johannes Thumshirn <[e-mail]>
Cc: Alan Stern <[e-mail]>
Cc: <[e-mail]>
Tested-by: Johannes Thumshirn <[e-mail]>
Reviewed-by: Johannes Thumshirn <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/sr.c

···
 static int sr_block_open(struct block_device *bdev, fmode_t mode)
 {
 	struct scsi_cd *cd;
+	struct scsi_device *sdev;
 	int ret = -ENXIO;
 
+	cd = scsi_cd_get(bdev->bd_disk);
+	if (!cd)
+		goto out;
+
+	sdev = cd->device;
+	scsi_autopm_get_device(sdev);
 	check_disk_change(bdev);
 
 	mutex_lock(&sr_mutex);
-	cd = scsi_cd_get(bdev->bd_disk);
-	if (cd) {
-		ret = cdrom_open(&cd->cdi, bdev, mode);
-		if (ret)
-			scsi_cd_put(cd);
-	}
+	ret = cdrom_open(&cd->cdi, bdev, mode);
 	mutex_unlock(&sr_mutex);
+
+	scsi_autopm_put_device(sdev);
+	if (ret)
+		scsi_cd_put(cd);
+
+out:
 	return ret;
 }
 
···
 	if (ret)
 		goto out;
 
+	scsi_autopm_get_device(sdev);
+
 	/*
 	 * Send SCSI addressing ioctls directly to mid level, send other
 	 * ioctls to cdrom/block level.
···
 	case SCSI_IOCTL_GET_IDLUN:
 	case SCSI_IOCTL_GET_BUS_NUMBER:
 		ret = scsi_ioctl(sdev, cmd, argp);
-		goto out;
+		goto put;
 	}
 
 	ret = cdrom_ioctl(&cd->cdi, bdev, mode, cmd, arg);
 	if (ret != -ENOSYS)
-		goto out;
+		goto put;
 
 	ret = scsi_ioctl(sdev, cmd, argp);
+
+put:
+	scsi_autopm_put_device(sdev);
 
 out:
 	mutex_unlock(&sr_mutex);