3.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Steven Whitehouse <swhit...@redhat.com>
commit dfd11184d894cd0a92397b25cac18831a1a6a5bc upstream.
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 <swhit...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
fs/gfs2/aops.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -1012,6 +1012,7 @@ static ssize_t gfs2_direct_IO(int rw, st
{
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;
@@ -1032,6 +1033,35 @@ static ssize_t gfs2_direct_IO(int rw, st
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);
--
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