svn commit: r253218 - stable/9/sys/fs/ext2fs

[Pedro F. Giffuni]

Author: pfg
Date: Thu Jul 11 19:18:13 2013
New Revision: 253218
URL: http://svnweb.freebsd.org/changeset/base/253218

Log:
  MFC	r253050:
  
  Enhancement when writing an entire block of a file (from UFS r231313).
  
  This change first attempts the uiomove() to the newly allocated
  (and dirty) buffer and only zeros it if the uiomove() fails. The
  effect is to eliminate the gratuitous zeroing of the buffer in
  the usual case where the uiomove() successfully fills it.

Modified:
  stable/9/sys/fs/ext2fs/ext2_vnops.c
Directory Properties:
  stable/9/sys/   (props changed)
  stable/9/sys/fs/   (props changed)

Modified: stable/9/sys/fs/ext2fs/ext2_vnops.c
==============================================================================
--- stable/9/sys/fs/ext2fs/ext2_vnops.c	Thu Jul 11 19:09:31 2013	(r253217)
+++ stable/9/sys/fs/ext2fs/ext2_vnops.c	Thu Jul 11 19:18:13 2013	(r253218)
@@ -1817,15 +1817,6 @@ ext2_write(struct vop_write_args *ap)
 		if (error != 0)
 			break;
 
-		/*
-		 * If the buffer is not valid and we did not clear garbage
-		 * out above, we have to do so here even though the write
-		 * covers the entire buffer in order to avoid a mmap()/write
-		 * race where another process may see the garbage prior to
-		 * the uiomove() for a write replacing it.
-		 */
-		if ((bp->b_flags & B_CACHE) == 0 && fs->e2fs_bsize <= xfersize)
-			vfs_bio_clrbuf(bp);
 		if ((ioflag & (IO_SYNC|IO_INVAL)) == (IO_SYNC|IO_INVAL))
 			bp->b_flags |= B_NOCACHE;
 		if (uio->uio_offset + xfersize > ip->i_size)
@@ -1836,6 +1827,26 @@ ext2_write(struct vop_write_args *ap)
 
 		error =
 		    uiomove((char *)bp->b_data + blkoffset, (int)xfersize, uio);
+		/*
+		 * If the buffer is not already filled and we encounter an
+		 * error while trying to fill it, we have to clear out any
+		 * garbage data from the pages instantiated for the buffer.
+		 * If we do not, a failed uiomove() during a write can leave
+		 * the prior contents of the pages exposed to a userland mmap.
+		 *
+		 * Note that we need only clear buffers with a transfer size
+		 * equal to the block size because buffers with a shorter
+		 * transfer size were cleared above by the call to ext2_balloc()
+		 * with the BA_CLRBUF flag set.
+		 *
+		 * If the source region for uiomove identically mmaps the
+		 * buffer, uiomove() performed the NOP copy, and the buffer
+		 * content remains valid because the page fault handler
+		 * validated the pages.
+		 */
+		if (error != 0 && (bp->b_flags & B_CACHE) == 0 &&
+		    fs->e2fs_bsize == xfersize)
+			vfs_bio_clrbuf(bp);
 		if (ioflag & (IO_VMIO|IO_DIRECT)) {
 			bp->b_flags |= B_RELBUF;
 		}