gfs2: Fix iomap write page reclaim deadlock

Since commit 64bc06bb32ee ("gfs2: iomap buffered write support"), gfs2 is doing
buffered writes by starting a transaction in iomap_begin, writing a range of
pages, and ending that transaction in iomap_end.  This approach suffers from
two problems:

  (1) Any allocations necessary for the write are done in iomap_begin, so when
  the data aren't journaled, there is no need for keeping the transaction open
  until iomap_end.

  (2) Transactions keep the gfs2 log flush lock held.  When
  iomap_file_buffered_write calls balance_dirty_pages, this can end up calling
  gfs2_write_inode, which will try to flush the log.  This requires taking the
  log flush lock which is already held, resulting in a deadlock.

Fix both of these issues by not keeping transactions open from iomap_begin to
iomap_end.  Instead, start a small transaction in page_prepare and end it in
page_done when necessary.

Reported-by: Edwin Török <edvin.torok@citrix.com>
Fixes: 64bc06bb32ee ("gfs2: iomap buffered write support")
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index 05dd78f4b2b3b..6210d4429d845 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -649,7 +649,7 @@ out_uninit:
  */
 void adjust_fs_space(struct inode *inode)
 {
-	struct gfs2_sbd *sdp = inode->i_sb->s_fs_info;
+	struct gfs2_sbd *sdp = GFS2_SB(inode);
 	struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
 	struct gfs2_inode *l_ip = GFS2_I(sdp->sd_sc_inode);
 	struct gfs2_statfs_change_host *m_sc = &sdp->sd_statfs_master;
@@ -657,10 +657,13 @@ void adjust_fs_space(struct inode *inode)
 	struct buffer_head *m_bh, *l_bh;
 	u64 fs_total, new_free;
 
+	if (gfs2_trans_begin(sdp, 2 * RES_STATFS, 0) != 0)
+		return;
+
 	/* Total up the file system space, according to the latest rindex. */
 	fs_total = gfs2_ri_total(sdp);
 	if (gfs2_meta_inode_buffer(m_ip, &m_bh) != 0)
-		return;
+		goto out;
 
 	spin_lock(&sdp->sd_statfs_spin);
 	gfs2_statfs_change_in(m_sc, m_bh->b_data +
@@ -675,11 +678,14 @@ void adjust_fs_space(struct inode *inode)
 	gfs2_statfs_change(sdp, new_free, new_free, 0);
 
 	if (gfs2_meta_inode_buffer(l_ip, &l_bh) != 0)
-		goto out;
+		goto out2;
 	update_statfs(sdp, m_bh, l_bh);
 	brelse(l_bh);
-out:
+out2:
 	brelse(m_bh);
+out:
+	sdp->sd_rindex_uptodate = 0;
+	gfs2_trans_end(sdp);
 }
 
 /**