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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Jeff Layton" <jlayton@redhat.com>,
        "Donatas Abraitis" <donatas.abraitis@gmail.com>,
        "Yan, Zheng" <zyan@redhat.com>,
        "Bryan Henderson" <bryanh@giraffe-data.com>,
        "Ilya Dryomov" <idryomov@gmail.com>
Date:   Sun, 11 Nov 2018 19:49:05 +0000
Message-ID: <lsq.1541965745.835092825@decadent.org.uk>
Subject: [PATCH 3.16 326/366] ceph: don't set req->r_locked_dir in
 ceph_d_revalidate
In-Reply-To: <lsq.1541965744.387173642@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Layton <jlayton@redhat.com>

commit c3f4688a08fd86f1bf8e055724c84b7a40a09733 upstream.

This function sets req->r_locked_dir which is supposed to indicate to
ceph_fill_trace that the parent's i_rwsem is locked for write.
Unfortunately, there is no guarantee that the dir will be locked when
d_revalidate is called, so we really don't want ceph_fill_trace to do
any dcache manipulation from this context. Clear req->r_locked_dir since
it's clearly not safe to do that.

What we really want to know with d_revalidate is whether the dentry
still points to the same inode. ceph_fill_trace installs a pointer to
the inode in req->r_target_inode, so we can just compare that to
d_inode(dentry) to see if it's the same one after the lookup.

Also, since we aren't generally interested in the parent here, we can
switch to using a GETATTR to hint that to the MDS, which also means that
we only need to reserve one cap.

Finally, just remove the d_unhashed check. That's really outside the
purview of a filesystem's d_revalidate. If the thing became unhashed
while we're checking it, then that's up to the VFS to handle anyway.

Fixes: 200fd27c8fa2 ("ceph: use lookup request to revalidate dentry")
Link: http://tracker.ceph.com/issues/18041
Reported-by: Donatas Abraitis <donatas.abraitis@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Cc: Bryan Henderson <bryanh@giraffe-data.com>
[bwh: Backported to 3.16: s/d_really_is_(positive|negative)/d_is_\1/ since
 we don't have to consider overlayfs]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 fs/ceph/dir.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -1071,26 +1071,30 @@ static int ceph_d_revalidate(struct dent
 		int op, mask, err;
 
 		op = ceph_snap(dir) == CEPH_SNAPDIR ?
-			CEPH_MDS_OP_LOOKUPSNAP : CEPH_MDS_OP_LOOKUP;
+			CEPH_MDS_OP_LOOKUPSNAP : CEPH_MDS_OP_GETATTR;
 		req = ceph_mdsc_create_request(mdsc, op, USE_ANY_MDS);
 		if (!IS_ERR(req)) {
 			req->r_dentry = dget(dentry);
-			req->r_num_caps = 2;
+			req->r_num_caps = op == CEPH_MDS_OP_GETATTR ? 1 : 2;
 
 			mask = CEPH_STAT_CAP_INODE | CEPH_CAP_AUTH_SHARED;
 			if (ceph_security_xattr_wanted(dir))
 				mask |= CEPH_CAP_XATTR_SHARED;
 			req->r_args.getattr.mask = mask;
 
-			req->r_locked_dir = dir;
 			err = ceph_mdsc_do_request(mdsc, NULL, req);
-			if (err == 0 || err == -ENOENT) {
-				if (dentry == req->r_dentry) {
-					valid = !d_unhashed(dentry);
-				} else {
-					d_invalidate(req->r_dentry);
-					err = -EAGAIN;
-				}
+			switch (err) {
+			case 0:
+				if (d_is_positive(dentry) &&
+				    d_inode(dentry) == req->r_target_inode)
+					valid = 1;
+				break;
+			case -ENOENT:
+				if (d_is_negative(dentry))
+					valid = 1;
+				/* Fallthrough */
+			default:
+				break;
 			}
 			ceph_mdsc_put_request(req);
 			dout("d_revalidate %p lookup result=%d\n",