master - lvmetad: Fix a race in metadata update.

[Petr Rockai]

Gitweb:        http://git.fedorahosted.org/git/?p=lvm2.git;a=commitdiff;h=15fdd5c90dda7f00f...
Commit:        15fdd5c90dda7f00f691668c13d5401206d22021
Parent:        6fc596ca90640817fd555942bd5b5d3b7404a177
Author:        Petr Rockai 
AuthorDate:    Wed Jan 16 11:09:37 2013 +0100
Committer:     Petr Rockai 
CommitterDate: Wed Jan 16 11:19:33 2013 +0100

lvmetad: Fix a race in metadata update.

The idea is to avoid a period when an existing VG is not mapped to either the
old or the new name. (Note that the brief "blackout" was present even if the
name did not actually change.) We instead allow a brief overlap of a VG existing
under both names, i.e. a query for a VG might succeed but before a lock is
acquired the VG disappears.
---
 daemons/lvmetad/lvmetad-core.c |   18 ++++++++++--------
 1 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/daemons/lvmetad/lvmetad-core.c b/daemons/lvmetad/lvmetad-core.c
index cbd6b09..a789bad 100644
--- a/daemons/lvmetad/lvmetad-core.c
+++ b/daemons/lvmetad/lvmetad-core.c
@@ -454,7 +454,8 @@ static response vg_lookup(lvmetad_state *s, request r)

DEBUGLOG(s, "vg_lookup: updated uuid = %s, name = %s", uuid, name);

-	if (!uuid)
+	/* Check the name here. */
+	if (!uuid || !name)
    	return reply_unknown("VG not found");

cft = lock_vg(s, uuid);
@@ -682,16 +683,14 @@ static int update_metadata(lvmetad_state *s, const char *name, const char *_vgid

lock_vgid_to_metadata(s);
    old = dm_hash_lookup(s->vgid_to_metadata, _vgid);
+	oldname = dm_hash_lookup(s->vgid_to_vgname, _vgid);
    unlock_vgid_to_metadata(s);
    lock_vg(s, _vgid);

seq = dm_config_find_int(metadata, "metadata/seqno", -1);

-	if (old) {
+	if (old)
    	haveseq = dm_config_find_int(old->root, "metadata/seqno", -1);
-		oldname = dm_hash_lookup(s->vgid_to_vgname, _vgid);
-		assert(oldname);
-	}

if (seq < 0)
    	goto out;
@@ -743,7 +742,7 @@ static int update_metadata(lvmetad_state *s, const char *name, const char *_vgid
    if (haveseq >= 0 && haveseq < seq) {
    	INFO(s, "Updating metadata for %s at %d to %d", _vgid, haveseq, seq);
    	/* temporarily orphan all of our PVs */
-		remove_metadata(s, vgid, 1);
+		update_pvid_to_vgid(s, old, "#orphan", 0);
    }

lock_vgid_to_metadata(s);
@@ -753,14 +752,17 @@ static int update_metadata(lvmetad_state *s, const char *name, const char *_vgid
    	  dm_hash_insert(s->vgid_to_metadata, vgid, cft) &&
    	  dm_hash_insert(s->vgid_to_vgname, vgid, cfgname) &&
    	  dm_hash_insert(s->vgname_to_vgid, name, (void*) vgid)) ? 1 : 0;
+
+	if (retval && oldname && strcmp(name, oldname))
+		dm_hash_remove(s->vgname_to_vgid, oldname);
+
    unlock_vgid_to_metadata(s);

if (retval)
-		/* FIXME: What should happen when update fails */
    	retval = update_pvid_to_vgid(s, cft, vgid, 1);

unlock_pvid_to_vgid(s);
-out:
+out: /* FIXME: We should probably abort() on partial failures. */
    if (!retval && cft)
    	dm_config_destroy(cft);
    unlock_vg(s, _vgid);