[GFS2] Fix a page lock / glock deadlock

We've previously been using a "try lock" in readpage on the basis that
it would prevent deadlocks due to the inverted lock ordering (our normal
lock ordering is glock first and then page lock). Unfortunately tests
have shown that this isn't enough. If the glock has a demote request
queued such that run_queue() in the glock code tries to do a demote when
its called under readpage then it will try and write out all the dirty
pages which requires locking them. This then deadlocks with the page
locked by readpage.

The solution is to always require two calls into readpage. The first
unlocks the page, gets the glock and returns AOP_TRUNCATED_PAGE, the
second does the actual readpage and unlocks the glock & page as
required.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/gfs2/ops_dentry.c b/fs/gfs2/ops_dentry.c
index 793e334d098e..4a5e676b4420 100644
--- a/fs/gfs2/ops_dentry.c
+++ b/fs/gfs2/ops_dentry.c
@@ -43,7 +43,7 @@ static int gfs2_drevalidate(struct dentry *dentry, struct nameidata *nd)
         struct gfs2_holder d_gh;
         struct gfs2_inode *ip = NULL;
         int error;
-        int had_lock=0;
+        int had_lock = 0;
 
         if (inode) {
                 if (is_bad_inode(inode))
@@ -54,7 +54,7 @@ static int gfs2_drevalidate(struct dentry *dentry, struct nameidata *nd)
         if (sdp->sd_args.ar_localcaching)
                 goto valid;
 
-        had_lock = gfs2_glock_is_locked_by_me(dip->i_gl);
+        had_lock = (gfs2_glock_is_locked_by_me(dip->i_gl) != NULL);
         if (!had_lock) {
                 error = gfs2_glock_nq_init(dip->i_gl, LM_ST_SHARED, 0, &d_gh);
                 if (error)