nfs/localio: Ensure DIO WRITE's IO on stable storage upon completion

LOCALIO's misaligned DIO WRITE support requires synchronous IO for any
misaligned head and/or tail that are issued using buffered IO.  In
addition, it is important that the O_DIRECT middle be on stable
storage upon its completion via AIO.

Otherwise, a misaligned DIO WRITE could mix buffered IO for the
head/tail and direct IO for the DIO-aligned middle -- which could lead
to problems associated with deferred writes to stable storage (such as
out of order partial completions causing incorrect advancement of the
file's offset, etc).

Fixes: c817248 ("nfs/localio: add proper O_DIRECT support for READ and WRITE")
Signed-off-by: Mike Snitzer <[email protected]>
Signed-off-by: Anna Schumaker <[email protected]>

Author: Mike Snitzer

fs/nfs/localio.c

@@ -485,8 +485,12 @@ nfs_local_iters_init(struct nfs_local_kiocb *iocb, int rw)
 		struct nfs_local_dio local_dio;
 
 		if (nfs_is_local_dio_possible(iocb, rw, len, &local_dio) &&
-		    nfs_local_iters_setup_dio(iocb, rw, v, len, &local_dio) != 0)
+		    nfs_local_iters_setup_dio(iocb, rw, v, len, &local_dio) != 0) {
+			/* Ensure DIO WRITE's IO on stable storage upon completion */
+			if (rw == ITER_SOURCE)
+				iocb->kiocb.ki_flags |= IOCB_DSYNC|IOCB_SYNC;
 			return; /* is DIO-aligned */
+		}
 	}
 
 	/* Use buffered IO */