svn commit: r318485 - stable/11/sys/kern

[Edward Tomasz Napierala]

Author: trasz
Date: Thu May 18 20:29:47 2017
New Revision: 318485
URL: https://svnweb.freebsd.org/changeset/base/318485

Log:
  MFC r316941:
  
  Don't try to write out bufs that have already failed with ENXIO.
  This fixes some panics after disconnecting mounted disks.

Modified:
  stable/11/sys/kern/vfs_bio.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/kern/vfs_bio.c
==============================================================================
--- stable/11/sys/kern/vfs_bio.c	Thu May 18 20:15:35 2017	(r318484)
+++ stable/11/sys/kern/vfs_bio.c	Thu May 18 20:29:47 2017	(r318485)
@@ -2303,18 +2303,28 @@ brelse(struct buf *bp)
 		bdirty(bp);
 	}
 	if (bp->b_iocmd == BIO_WRITE && (bp->b_ioflags & BIO_ERROR) &&
+	    (bp->b_error != ENXIO || !LIST_EMPTY(&bp->b_dep)) &&
 	    !(bp->b_flags & B_INVAL)) {
 		/*
-		 * Failed write, redirty.  Must clear BIO_ERROR to prevent
-		 * pages from being scrapped.
+		 * Failed write, redirty.  All errors except ENXIO (which
+		 * means the device is gone) are expected to be potentially
+		 * transient - underlying media might work if tried again
+		 * after EIO, and memory might be available after an ENOMEM.
+		 *
+		 * Do this also for buffers that failed with ENXIO, but have
+		 * non-empty dependencies - the soft updates code might need
+		 * to access the buffer to untangle them.
+		 *
+		 * Must clear BIO_ERROR to prevent pages from being scrapped.
 		 */
 		bp->b_ioflags &= ~BIO_ERROR;
 		bdirty(bp);
 	} else if ((bp->b_flags & (B_NOCACHE | B_INVAL)) ||
 	    (bp->b_ioflags & BIO_ERROR) || (bp->b_bufsize <= 0)) {
 		/*
-		 * Either a failed read I/O or we were asked to free or not
-		 * cache the buffer.
+		 * Either a failed read I/O, or we were asked to free or not
+		 * cache the buffer, or we failed to write to a device that's
+		 * no longer present.
 		 */
 		bp->b_flags |= B_INVAL;
 		if (!LIST_EMPTY(&bp->b_dep))