svn commit: r342375 - head/sys/dev/md

[Bruce Evans]

Author: bde
Date: Sat Dec 22 22:59:11 2018
New Revision: 342375
URL: https://svnweb.freebsd.org/changeset/base/342375

Log:
  Fix devstat on md devices, second attempt.  r341765 depends on
  g_io_deliver() finishing initialization of the bio, but g_io_deliver()
  actually destroys the bio.  INVARIANTS makes the bug obvious by
  overwriting the bio with garbage.
  
  Restore the old order for calling devstat (except don't restore not calling
  it for the error case), and translate to the devstat KPI so that this order
  works.
  
  Reviewed by:	kib

Modified:
  head/sys/dev/md/md.c

Modified: head/sys/dev/md/md.c
==============================================================================
--- head/sys/dev/md/md.c	Sat Dec 22 21:49:25 2018	(r342374)
+++ head/sys/dev/md/md.c	Sat Dec 22 22:59:11 2018	(r342375)
@@ -1241,12 +1241,22 @@ md_kthread(void *arg)
 			error = sc->start(sc, bp);
 		}
 
+		if (bp->bio_cmd == BIO_READ || bp->bio_cmd == BIO_WRITE) {
+			/*
+			 * Devstat uses (bio_bcount, bio_resid) for
+			 * determining the length of the completed part of
+			 * the i/o.  g_io_deliver() will translate from
+			 * bio_completed to that, but it also destroys the
+			 * bio so we must do our own translation.
+			 */
+			bp->bio_bcount = bp->bio_length;
+			bp->bio_resid = (error == -1 ? bp->bio_bcount : 0);
+			devstat_end_transaction_bio(sc->devstat, bp);
+		}
 		if (error != -1) {
 			bp->bio_completed = bp->bio_length;
 			g_io_deliver(bp, error);
 		}
-		if (bp->bio_cmd == BIO_READ || bp->bio_cmd == BIO_WRITE)
-			devstat_end_transaction_bio(sc->devstat, bp);
 	}
 }