[PATCH] direct-io: sync and invalidate file region when falling back to buffered write

When direct-io falls back to buffered write, it will just leave the dirty data
floating about in pagecache, pending regular writeback.

But normal direct-io semantics are that IO is synchronous, and that it leaves
no pagecache behind.

So change the fallback-to-buffered-write code to sync the file region and to
then strip away the pagecache, just as a regular direct-io write would do.

Acked-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Zach Brown <zach.brown@oracle.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 45 insertions, 6 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 3464b681f844..57faa8d12099 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2222,7 +2222,7 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
                                 unsigned long nr_segs, loff_t *ppos)
 {
         struct file *file = iocb->ki_filp;
-        const struct address_space * mapping = file->f_mapping;
+        struct address_space * mapping = file->f_mapping;
         size_t ocount;          /* original count */
         size_t count;           /* after file limit checks */
         struct inode    *inode = mapping->host;
@@ -2275,8 +2275,11 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
 
         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
         if (unlikely(file->f_flags & O_DIRECT)) {
-                written = generic_file_direct_write(iocb, iov,
-                                &nr_segs, pos, ppos, count, ocount);
+                loff_t endbyte;
+                ssize_t written_buffered;
+
+                written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
+                                                        ppos, count, ocount);
                 if (written < 0 || written == count)
                         goto out;
                 /*
@@ -2285,10 +2288,46 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
                  */
                 pos += written;
                 count -= written;
-        }
+                written_buffered = generic_file_buffered_write(iocb, iov,
+                                                nr_segs, pos, ppos, count,
+                                                written);
+                /*
+                 * If generic_file_buffered_write() retuned a synchronous error
+                 * then we want to return the number of bytes which were
+                 * direct-written, or the error code if that was zero.  Note
+                 * that this differs from normal direct-io semantics, which
+                 * will return -EFOO even if some bytes were written.
+                 */
+                if (written_buffered < 0) {
+                        err = written_buffered;
+                        goto out;
+                }
 
-        written = generic_file_buffered_write(iocb, iov, nr_segs,
-                        pos, ppos, count, written);
+                /*
+                 * We need to ensure that the page cache pages are written to
+                 * disk and invalidated to preserve the expected O_DIRECT
+                 * semantics.
+                 */
+                endbyte = pos + written_buffered - written - 1;
+                err = do_sync_file_range(file, pos, endbyte,
+                                         SYNC_FILE_RANGE_WAIT_BEFORE|
+                                         SYNC_FILE_RANGE_WRITE|
+                                         SYNC_FILE_RANGE_WAIT_AFTER);
+                if (err == 0) {
+                        written = written_buffered;
+                        invalidate_mapping_pages(mapping,
+                                                 pos >> PAGE_CACHE_SHIFT,
+                                                 endbyte >> PAGE_CACHE_SHIFT);
+                } else {
+                        /*
+                         * We don't know how much we wrote, so just return
+                         * the number of bytes which were direct-written
+                         */
+                }
+        } else {
+                written = generic_file_buffered_write(iocb, iov, nr_segs,
+                                pos, ppos, count, written);
+        }
 out:
         current->backing_dev_info = NULL;
         return written ? written : err;