Make wait_for_device_probe() also do scsi_complete_async_scans()

Commit a7a20d103994 ("sd: limit the scope of the async probe domain")
make the SCSI device probing run device discovery in it's own async
domain.

However, as a result, the partition detection was no longer synchronized
by async_synchronize_full() (which, despite the name, only synchronizes
the global async space, not all of them).  Which in turn meant that
"wait_for_device_probe()" would not wait for the SCSI partitions to be
parsed.

And "wait_for_device_probe()" was what the boot time init code relied on
for mounting the root filesystem.

Now, most people never noticed this, because not only is it
timing-dependent, but modern distributions all use initrd.  So the root
filesystem isn't actually on a disk at all.  And then before they
actually mount the final disk filesystem, they will have loaded the
scsi-wait-scan module, which not only does the expected
wait_for_device_probe(), but also does scsi_complete_async_scans().

[ Side note: scsi_complete_async_scans() had also been partially broken,
  but that was fixed in commit 43a8d39d0137 ("fix async probe
  regression"), so that same commit a7a20d103994 had actually broken
  setups even if you used scsi-wait-scan explicitly ]

Solve this problem by just moving the scsi_complete_async_scans() call
into wait_for_device_probe().  Everybody who wants to wait for device
probing to finish really wants the SCSI probing to complete, so there's
no reason not to do this.

So now "wait_for_device_probe()" really does what the name implies, and
properly waits for device probing to finish.  This also removes the now
unnecessary extra calls to scsi_complete_async_scans().

Reported-and-tested-by: Artem S. Tashkinov <t.artem@mailcity.com>
Cc: Dan Williams <dan.j.williams@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: James Bottomley <jbottomley@parallels.com>
Cc: Borislav Petkov <bp@amd64.org>
Cc: linux-scsi <linux-scsi@vger.kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 5 deletions

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index dcb8a6e48692..4b01ab3d2c24 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -24,6 +24,7 @@
 #include <linux/wait.h>
 #include <linux/async.h>
 #include <linux/pm_runtime.h>
+#include <scsi/scsi_scan.h>
 
 #include "base.h"
 #include "power/power.h"
@@ -332,6 +333,7 @@ void wait_for_device_probe(void)
         /* wait for the known devices to complete their probing */
         wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
         async_synchronize_full();
+        scsi_complete_async_scans();
 }
 EXPORT_SYMBOL_GPL(wait_for_device_probe);
 
diff --git a/drivers/scsi/scsi_wait_scan.c b/drivers/scsi/scsi_wait_scan.c
index ae7814874618..072734538876 100644
--- a/drivers/scsi/scsi_wait_scan.c
+++ b/drivers/scsi/scsi_wait_scan.c
@@ -22,11 +22,6 @@ static int __init wait_scan_init(void)
          * and might not yet have reached the scsi async scanning
          */
         wait_for_device_probe();
-        /*
-         * and then we wait for the actual asynchronous scsi scan
-         * to finish.
-         */
-        scsi_complete_async_scans();
         return 0;
 }