| Message ID | 1389886553.2779.32.camel@menhir |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jan 16, 2014 at 4:35 PM, Steven Whitehouse <swhiteho@redhat.com> wrote: > > Following on from the "Re: [PATCH v3] vfs: fix a bug when we do some dio > reads with append dio writes" thread on linux-fsdevel, this patch is my > current version of the fix proposed as option (b) in that thread. > > Removing the i_size test from the direct i/o read path at VFS level > means that filesystems now have to deal with requests which are beyond > i_size themselves. These I've divided into three sets: > > a) Those with "no op" ->direct_IO (9p, cifs, ceph) > These are obviously not going to be an issue > > b) Those with "home brew" ->direct_IO (nfs, fuse) > I've been told that NFS should not have any problem with the larger > i_size, however I've added an extra test to FUSE to duplicate the > original behaviour just to be on the safe side. Someone who knows fuse > better maybe able to confirm whether this is actually required or not. > > c) Those using __blockdev_direct_IO() > These call through to ->get_block() which should deal with the EOF > condition correctly. I've verified that with GFS2 and I believe that > Zheng has verified it for ext4. I've also run the test on XFS and it > passes both before and after this change. > > The part of the patch in filemap.c looks a lot larger than it really is > - there are only two lines of real change. The rest is just indentation > of the contained code. > > There remains a test of i_size though, which was added for btrfs. It > doesn't cause the other filesystems a problem as the test is performed > after ->direct_IO has been called. It is possible that there is a race > that does matter to btrfs, however this patch doesn't change that, so > its still an overall improvement. > > So please have a look at this and let me know what you think. I guess > that when time comes to submit it, it should probably be via the vfs > tree. > > Signed-off-by: Steven Whitehouse <swhiteho@redhat.com> > Reported-by: Zheng Liu <gnehzuil.liu@gmail.com> > Cc: Jan Kara <jack@suse.cz> > Cc: Dave Chinner <david@fromorbit.com> > Cc: Miklos Szeredi <miklos@szeredi.hu> > Cc: Chris Mason <clm@fb.com> > Cc: Josef Bacik <jbacik@fb.com> > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 7e70506..89fdfd1 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -2710,6 +2710,9 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, > inode = file->f_mapping->host; > i_size = i_size_read(inode); > > + if ((rw == READ) && (offset > i_size)) > + return 0; > + Hmm, OK. It's not strictly needed, but a valid optimization. So ACK. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 7e70506..89fdfd1 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -2710,6 +2710,9 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, inode = file->f_mapping->host; i_size = i_size_read(inode); + if ((rw == READ) && (offset > i_size)) + return 0; + /* optimization for short read */ if (async_dio && rw != WRITE && offset + count > i_size) { if (offset >= i_size) diff --git a/mm/filemap.c b/mm/filemap.c index b7749a9..0184286 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1428,30 +1428,28 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov, if (!count) goto out; /* skip atime */ size = i_size_read(inode); - if (pos < size) { - retval = filemap_write_and_wait_range(mapping, pos, + retval = filemap_write_and_wait_range(mapping, pos, pos + iov_length(iov, nr_segs) - 1); - if (!retval) { - retval = mapping->a_ops->direct_IO(READ, iocb, - iov, pos, nr_segs); - } - if (retval > 0) { - *ppos = pos + retval; - count -= retval; - } + if (!retval) { + retval = mapping->a_ops->direct_IO(READ, iocb, + iov, pos, nr_segs); + } + if (retval > 0) { + *ppos = pos + retval; + count -= retval; + } - /* - * Btrfs can have a short DIO read if we encounter - * compressed extents, so if there was an error, or if - * we've already read everything we wanted to, or if - * there was a short read because we hit EOF, go ahead - * and return. Otherwise fallthrough to buffered io for - * the rest of the read. - */ - if (retval < 0 || !count || *ppos >= size) { - file_accessed(filp); - goto out; - } + /* + * Btrfs can have a short DIO read if we encounter + * compressed extents, so if there was an error, or if + * we've already read everything we wanted to, or if + * there was a short read because we hit EOF, go ahead + * and return. Otherwise fallthrough to buffered io for + * the rest of the read. + */ + if (retval < 0 || !count || *ppos >= size) { + file_accessed(filp); + goto out; } }
Following on from the "Re: [PATCH v3] vfs: fix a bug when we do some dio reads with append dio writes" thread on linux-fsdevel, this patch is my current version of the fix proposed as option (b) in that thread. Removing the i_size test from the direct i/o read path at VFS level means that filesystems now have to deal with requests which are beyond i_size themselves. These I've divided into three sets: a) Those with "no op" ->direct_IO (9p, cifs, ceph) These are obviously not going to be an issue b) Those with "home brew" ->direct_IO (nfs, fuse) I've been told that NFS should not have any problem with the larger i_size, however I've added an extra test to FUSE to duplicate the original behaviour just to be on the safe side. Someone who knows fuse better maybe able to confirm whether this is actually required or not. c) Those using __blockdev_direct_IO() These call through to ->get_block() which should deal with the EOF condition correctly. I've verified that with GFS2 and I believe that Zheng has verified it for ext4. I've also run the test on XFS and it passes both before and after this change. The part of the patch in filemap.c looks a lot larger than it really is - there are only two lines of real change. The rest is just indentation of the contained code. There remains a test of i_size though, which was added for btrfs. It doesn't cause the other filesystems a problem as the test is performed after ->direct_IO has been called. It is possible that there is a race that does matter to btrfs, however this patch doesn't change that, so its still an overall improvement. So please have a look at this and let me know what you think. I guess that when time comes to submit it, it should probably be via the vfs tree. Signed-off-by: Steven Whitehouse <swhiteho@redhat.com> Reported-by: Zheng Liu <gnehzuil.liu@gmail.com> Cc: Jan Kara <jack@suse.cz> Cc: Dave Chinner <david@fromorbit.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Chris Mason <clm@fb.com> Cc: Josef Bacik <jbacik@fb.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html