GFS2: Fix incorrect invalidation for DIO/buffered I/O

In patch 209806aba9d540dde3db0a5ce72307f85f33468f we allowed
local deferred locks to be granted against a cached exclusive
lock. That opened up a corner case which this patch now
fixes.

The solution to the problem is to check whether we have cached
pages each time we do direct I/O and if so to unmap, flush
and invalidate those pages. Since the glock state machine
normally does that for us, mostly the code will be a no-op.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index b7fc035a6943..73f3e4ee4037 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -986,6 +986,7 @@ static ssize_t gfs2_direct_IO(int rw, struct kiocb *iocb,
 {
         struct file *file = iocb->ki_filp;
         struct inode *inode = file->f_mapping->host;
+        struct address_space *mapping = inode->i_mapping;
         struct gfs2_inode *ip = GFS2_I(inode);
         struct gfs2_holder gh;
         int rv;
@@ -1006,6 +1007,35 @@ static ssize_t gfs2_direct_IO(int rw, struct kiocb *iocb,
         if (rv != 1)
                 goto out; /* dio not valid, fall back to buffered i/o */
 
+        /*
+         * Now since we are holding a deferred (CW) lock at this point, you
+         * might be wondering why this is ever needed. There is a case however
+         * where we've granted a deferred local lock against a cached exclusive
+         * glock. That is ok provided all granted local locks are deferred, but
+         * it also means that it is possible to encounter pages which are
+         * cached and possibly also mapped. So here we check for that and sort
+         * them out ahead of the dio. The glock state machine will take care of
+         * everything else.
+         *
+         * If in fact the cached glock state (gl->gl_state) is deferred (CW) in
+         * the first place, mapping->nr_pages will always be zero.
+         */
+        if (mapping->nrpages) {
+                loff_t lstart = offset & (PAGE_CACHE_SIZE - 1);
+                loff_t len = iov_length(iov, nr_segs);
+                loff_t end = PAGE_ALIGN(offset + len) - 1;
+
+                rv = 0;
+                if (len == 0)
+                        goto out;
+                if (test_and_clear_bit(GIF_SW_PAGED, &ip->i_flags))
+                        unmap_shared_mapping_range(ip->i_inode.i_mapping, offset, len);
+                rv = filemap_write_and_wait_range(mapping, lstart, end);
+                if (rv)
+                        return rv;
+                truncate_inode_pages_range(mapping, lstart, end);
+        }
+
         rv = __blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
                                   offset, nr_segs, gfs2_get_block_direct,
                                   NULL, NULL, 0);