It is possible to receive an update to the snaprealms hierarchy from an MDS while walking through this hierarchy. This patch adds a mechanism similar to the one used in dcache to detect renames in lookups. A new seqlock is used to allow a retry in case a change has occurred while walking through the snaprealms. Link: http://tracker.ceph.com/issues/22372 Signed-off-by: Luis Henriques <lhenriques@xxxxxxxx> --- fs/ceph/snap.c | 45 +++++++++++++++++++++++++++++++++++++++------ fs/ceph/super.h | 2 ++ 2 files changed, 41 insertions(+), 6 deletions(-) diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c index 8a2ca41e4b97..8b9d6c7c0df4 100644 --- a/fs/ceph/snap.c +++ b/fs/ceph/snap.c @@ -54,6 +54,25 @@ * console). */ +/* + * While walking through the snaprealm hierarchy it is possible that + * this hierarchy is updated (for ex, when a different client moves + * directories around). snaprealm_lock isn't supposed to prevent this + * but, just like the rename_lock in dcache, to detect that this has + * happen so that a lookup can be retried. + * + * Here's a typical usage pattern for this lock: + * + * retry: + * seq = read_seqbegin(&snaprealm_lock); + * realm = ci->i_snap_realm; + * ceph_get_snap_realm(mdsc, realm); + * ... do stuff ... + * ceph_put_snap_realm(mdsc, realm); + * if (read_seqretry(&snaprealm_lock, seq)) + * goto retry; + */ +DEFINE_SEQLOCK(snaprealm_lock); /* * increase ref count for the realm @@ -81,10 +100,12 @@ void ceph_get_snap_realm(struct ceph_mds_client *mdsc, static void __insert_snap_realm(struct rb_root *root, struct ceph_snap_realm *new) { - struct rb_node **p = &root->rb_node; + struct rb_node **p; struct rb_node *parent = NULL; struct ceph_snap_realm *r = NULL; + write_seqlock(&snaprealm_lock); + p = &root->rb_node; while (*p) { parent = *p; r = rb_entry(parent, struct ceph_snap_realm, node); @@ -98,6 +119,7 @@ static void __insert_snap_realm(struct rb_root *root, rb_link_node(&new->node, parent, p); rb_insert_color(&new->node, root); + write_sequnlock(&snaprealm_lock); } /* @@ -136,9 +158,14 @@ static struct ceph_snap_realm *ceph_create_snap_realm( static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc, u64 ino) { - struct rb_node *n = mdsc->snap_realms.rb_node; - struct ceph_snap_realm *r; - + struct rb_node *n; + struct ceph_snap_realm *realm, *r; + unsigned seq; + +retry: + realm = NULL; + seq = read_seqbegin(&snaprealm_lock); + n = mdsc->snap_realms.rb_node; while (n) { r = rb_entry(n, struct ceph_snap_realm, node); if (ino < r->ino) @@ -147,10 +174,14 @@ static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc, n = n->rb_right; else { dout("lookup_snap_realm %llx %p\n", r->ino, r); - return r; + realm = r; + break; } } - return NULL; + + if (read_seqretry(&snaprealm_lock, seq)) + goto retry; + return realm; } struct ceph_snap_realm *ceph_lookup_snap_realm(struct ceph_mds_client *mdsc, @@ -174,7 +205,9 @@ static void __destroy_snap_realm(struct ceph_mds_client *mdsc, { dout("__destroy_snap_realm %p %llx\n", realm, realm->ino); + write_seqlock(&snaprealm_lock); rb_erase(&realm->node, &mdsc->snap_realms); + write_sequnlock(&snaprealm_lock); if (realm->parent) { list_del_init(&realm->child_item); diff --git a/fs/ceph/super.h b/fs/ceph/super.h index 2beeec07fa76..6474e8d875b7 100644 --- a/fs/ceph/super.h +++ b/fs/ceph/super.h @@ -760,6 +760,8 @@ static inline int default_congestion_kb(void) /* snap.c */ +extern seqlock_t snaprealm_lock; + struct ceph_snap_realm *ceph_lookup_snap_realm(struct ceph_mds_client *mdsc, u64 ino); extern void ceph_get_snap_realm(struct ceph_mds_client *mdsc, -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
