PM/Hibernate: Wait for SCSI devices scan to complete during resume

There is a race between resume from hibernation and the asynchronous
scanning of SCSI devices and to prevent it from happening we need to
call scsi_complete_async_scans() during resume from hibernation.

In addition, if the resume from hibernation is userland-driven, it's
better to wait for all device probes in the kernel to complete before
attempting to open the resume device.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/scsi/scsi_priv.h

@@ -38,9 +38,6 @@ static inline void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
 	{ };
 #endif
 
-/* scsi_scan.c */
-int scsi_complete_async_scans(void);
-
 /* scsi_devinfo.c */
 extern int scsi_get_device_flags(struct scsi_device *sdev,
 				 const unsigned char *vendor,

drivers/scsi/scsi_wait_scan.c

@@ -11,7 +11,7 @@
  */
 
 #include <linux/module.h>
-#include "scsi_priv.h"
+#include <scsi/scsi_scan.h>
 
 static int __init wait_scan_init(void)
 {

include/scsi/scsi_scan.h

@@ -0,0 +1,11 @@
+#ifndef _SCSI_SCSI_SCAN_H
+#define _SCSI_SCSI_SCAN_H
+
+#ifdef CONFIG_SCSI
+/* drivers/scsi/scsi_scan.c */
+extern int scsi_complete_async_scans(void);
+#else
+static inline int scsi_complete_async_scans(void) { return 0; }
+#endif
+
+#endif /* _SCSI_SCSI_SCAN_H */

kernel/power/disk.c

@@ -22,6 +22,7 @@
 #include <linux/console.h>
 #include <linux/cpu.h>
 #include <linux/freezer.h>
+#include <scsi/scsi_scan.h>
 #include <asm/suspend.h>
 
 #include "power.h"
@@ -644,6 +645,13 @@ static int software_resume(void)
 	if (noresume)
 		return 0;
 
+	/*
+	 * We can't depend on SCSI devices being available after loading one of
+	 * their modules if scsi_complete_async_scans() is not called and the
+	 * resume device usually is a SCSI one.
+	 */
+	scsi_complete_async_scans();
+
 	/*
 	 * name_to_dev_t() below takes a sysfs buffer mutex when sysfs
 	 * is configured into the kernel. Since the regular hibernate

kernel/power/user.c

@@ -24,6 +24,7 @@
 #include <linux/cpu.h>
 #include <linux/freezer.h>
 #include <linux/smp_lock.h>
+#include <scsi/scsi_scan.h>
 
 #include <asm/uaccess.h>
 
@@ -92,13 +93,21 @@ static int snapshot_open(struct inode *inode, struct file *filp)
 	filp->private_data = data;
 	memset(&data->handle, 0, sizeof(struct snapshot_handle));
 	if ((filp->f_flags & O_ACCMODE) == O_RDONLY) {
+		/* Hibernating.  The image device should be accessible. */
 		data->swap = swsusp_resume_device ?
 			swap_type_of(swsusp_resume_device, 0, NULL) : -1;
 		data->mode = O_RDONLY;
 		error = pm_notifier_call_chain(PM_HIBERNATION_PREPARE);
 		if (error)
 			pm_notifier_call_chain(PM_POST_HIBERNATION);
 	} else {
+		/*
+		 * Resuming.  We may need to wait for the image device to
+		 * appear.
+		 */
+		wait_for_device_probe();
+		scsi_complete_async_scans();
+
 		data->swap = -1;
 		data->mode = O_WRONLY;
 		error = pm_notifier_call_chain(PM_RESTORE_PREPARE);