ceph: introduce global empty snap context

Commit Message

Yan, Zheng Dec. 16, 2014, 8:43 a.m. UTC

> ? 2014?12?15??21:00?Ilya Dryomov <[e-mail]> ???
> 
> On Thu, Nov 13, 2014 at 11:23 PM, Ilya Dryomov <[e-mail]> wrote:
>> This patch wasn't posted on ceph-devel, posting..
> 
> Hi Zheng,
> 
> Ping - I had some comments (below), mostly trivial but a potential
> cached_context leak is what worries me.
> 
> Thanks,
> 
>               Ilya


here is the updated patch, thanks.

—
From 6de279d244d56b78da70efe7968b815db0f3bb5f Mon Sep 17 00:00:00 2001
From: "Yan, Zheng" <[e-mail]>
Date: Thu, 6 Nov 2014 15:09:41 +0800
Subject: [PATCH] ceph: introduce global empty snap context

Current snaphost code does not properly handle moving inode from one
empty snap realm to another empty snap realm. After changing inode's
snap realm, some dirty pages' snap context can be not equal to inode's
i_head_snap. This can trigger BUG() in ceph_put_wrbuffer_cap_refs()

The fix is introduce a global empty snap context for all empty snap
realm. This avoids triggering the BUG() for filesystem with no snapshot.

Fixes: http://tracker.ceph.com/issues/9928
Signed-off-by: Yan, Zheng <[e-mail]>
---
fs/ceph/snap.c  | 28 ++++++++++++++++++++++++++--
fs/ceph/super.c | 10 ++++++++--
fs/ceph/super.h |  2 ++
3 files changed, 36 insertions(+), 4 deletions(-)

Patch

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index c1cc993..3035b8f 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -288,6 +288,9 @@  static int cmpu64_rev(const void *a, const void *b)
	return 0;
}

+
+static struct ceph_snap_context *empty_snapc;
+
/*
 * build the snap context for a given realm.
 */
@@ -328,6 +331,12 @@  static int build_snap_context(struct ceph_snap_realm *realm)
		return 0;
	}

+	if (num == 0 && realm->seq == empty_snapc->seq) {
+		ceph_get_snap_context(empty_snapc);
+		snapc = empty_snapc;
+		goto done;
+	}
+
	/* alloc new snap context */
	err = -ENOMEM;
	if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
@@ -364,7 +373,7 @@  static int build_snap_context(struct ceph_snap_realm *realm)
	dout("build_snap_context %llx %p: %p seq %lld (%u snaps)\n",
	     realm->ino, realm, snapc, snapc->seq,
	     (unsigned int) snapc->num_snaps);
-
+done:
	ceph_put_snap_context(realm->cached_context);
	realm->cached_context = snapc;
	return 0;
@@ -465,6 +474,9 @@  void ceph_queue_cap_snap(struct ceph_inode_info *ci)
		   cap_snap.  lucky us. */
		dout("queue_cap_snap %p already pending\n", inode);
		kfree(capsnap);
+	} else if (ci->i_snap_realm->cached_context == empty_snapc) {
+		dout("queue_cap_snap %p empty snapc\n", inode);
+		kfree(capsnap);
	} else if (dirty & (CEPH_CAP_AUTH_EXCL|CEPH_CAP_XATTR_EXCL|
			    CEPH_CAP_FILE_EXCL|CEPH_CAP_FILE_WR)) {
		struct ceph_snap_context *snapc = ci->i_head_snapc;
@@ -925,5 +937,17 @@  out:
	return;
}

+int __init ceph_snap_init(void)
+{
+	empty_snapc = ceph_create_snap_context(0, GFP_NOFS);
+	if (!empty_snapc)
+		return -ENOMEM;
+	empty_snapc->seq = 1;
+	empty_snapc->num_snaps = 0;
+	return 0;
+}

-
+void ceph_snap_exit(void)
+{
+	ceph_put_snap_context(empty_snapc);
+}
diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index f6e1237..3b5c1e3 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -1028,15 +1028,20 @@  static int __init init_ceph(void)

	ceph_flock_init();
	ceph_xattr_init();
+	ret = ceph_snap_init();
+	if (ret)
+		goto out_xattr;
	ret = register_filesystem(&ceph_fs_type);
	if (ret)
-		goto out_icache;
+		goto out_snap;

	pr_info("loaded (mds proto %d)\n", CEPH_MDSC_PROTOCOL);

	return 0;

-out_icache:
+out_snap:
+	ceph_snap_exit();
+out_xattr:
	ceph_xattr_exit();
	destroy_caches();
out:
@@ -1047,6 +1052,7 @@  static void __exit exit_ceph(void)
{
	dout("exit_ceph\n");
	unregister_filesystem(&ceph_fs_type);
+	ceph_snap_exit();
	ceph_xattr_exit();
	destroy_caches();
}
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index aca2287..9f63f18 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -699,6 +699,8 @@  extern void ceph_queue_cap_snap(struct ceph_inode_info *ci);
extern int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
				  struct ceph_cap_snap *capsnap);
extern void ceph_cleanup_empty_realms(struct ceph_mds_client *mdsc);
+extern int __init ceph_snap_init(void);
+extern void ceph_snap_exit(void);

/*
 * a cap_snap is "pending" if it is still awaiting an in-progress