ceph: fix cap flush race reentrancy
In e9964c10 we change cap flushing to do a delicate dance because some
inodes on the cap_dirty list could be in a migrating state (got EXPORT but
not IMPORT) in which we couldn't actually flush and move from
dirty->flushing, breaking the while (!empty) { process first } loop
structure. It worked for a single sync thread, but was not reentrant and
triggered infinite loops when multiple syncers came along.
Instead, move inodes with dirty to a separate cap_dirty_migrating list
when in the limbo export-but-no-import state, allowing us to go back to
the simple loop structure (which was reentrant). This is cleaner and more
robust.
Audited the cap_dirty users and this looks fine:
list_empty(&ci->i_dirty_item) is still a reliable indicator of whether we
have dirty caps (which list we're on is irrelevant) and list_del_init()
calls still do the right thing.
Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 591202b..1f72b00 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -2635,6 +2635,7 @@
struct ceph_mds_session *session,
int *open_target_sessions)
{
+ struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
struct ceph_inode_info *ci = ceph_inode(inode);
int mds = session->s_mds;
unsigned mseq = le32_to_cpu(ex->migrate_seq);
@@ -2671,6 +2672,19 @@
* export targets, so that we get the matching IMPORT
*/
*open_target_sessions = 1;
+
+ /*
+ * we can't flush dirty caps that we've seen the
+ * EXPORT but no IMPORT for
+ */
+ spin_lock(&mdsc->cap_dirty_lock);
+ if (!list_empty(&ci->i_dirty_item)) {
+ dout(" moving %p to cap_dirty_migrating\n",
+ inode);
+ list_move(&ci->i_dirty_item,
+ &mdsc->cap_dirty_migrating);
+ }
+ spin_unlock(&mdsc->cap_dirty_lock);
}
__ceph_remove_cap(cap);
}
@@ -2708,6 +2722,13 @@
ci->i_cap_exporting_issued = 0;
ci->i_cap_exporting_mseq = 0;
ci->i_cap_exporting_mds = -1;
+
+ spin_lock(&mdsc->cap_dirty_lock);
+ if (!list_empty(&ci->i_dirty_item)) {
+ dout(" moving %p back to cap_dirty\n", inode);
+ list_move(&ci->i_dirty_item, &mdsc->cap_dirty);
+ }
+ spin_unlock(&mdsc->cap_dirty_lock);
} else {
dout("handle_cap_import inode %p ci %p mds%d mseq %d\n",
inode, ci, mds, mseq);
@@ -2911,38 +2932,16 @@
*/
void ceph_flush_dirty_caps(struct ceph_mds_client *mdsc)
{
- struct ceph_inode_info *ci, *nci = NULL;
- struct inode *inode, *ninode = NULL;
- struct list_head *p, *n;
+ struct ceph_inode_info *ci;
+ struct inode *inode;
dout("flush_dirty_caps\n");
spin_lock(&mdsc->cap_dirty_lock);
- list_for_each_safe(p, n, &mdsc->cap_dirty) {
- if (nci) {
- ci = nci;
- inode = ninode;
- ci->i_ceph_flags &= ~CEPH_I_NOFLUSH;
- dout("flush_dirty_caps inode %p (was next inode)\n",
- inode);
- } else {
- ci = list_entry(p, struct ceph_inode_info,
- i_dirty_item);
- inode = igrab(&ci->vfs_inode);
- BUG_ON(!inode);
- dout("flush_dirty_caps inode %p\n", inode);
- }
- if (n != &mdsc->cap_dirty) {
- nci = list_entry(n, struct ceph_inode_info,
- i_dirty_item);
- ninode = igrab(&nci->vfs_inode);
- BUG_ON(!ninode);
- nci->i_ceph_flags |= CEPH_I_NOFLUSH;
- dout("flush_dirty_caps next inode %p, noflush\n",
- ninode);
- } else {
- nci = NULL;
- ninode = NULL;
- }
+ while (!list_empty(&mdsc->cap_dirty)) {
+ ci = list_first_entry(&mdsc->cap_dirty, struct ceph_inode_info,
+ i_dirty_item);
+ inode = igrab(&ci->vfs_inode);
+ dout("flush_dirty_caps %p\n", inode);
spin_unlock(&mdsc->cap_dirty_lock);
if (inode) {
ceph_check_caps(ci, CHECK_CAPS_NODELAY|CHECK_CAPS_FLUSH,
@@ -2952,6 +2951,7 @@
spin_lock(&mdsc->cap_dirty_lock);
}
spin_unlock(&mdsc->cap_dirty_lock);
+ dout("flush_dirty_caps done\n");
}
/*
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index c12d2e9..79743d1 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -3004,6 +3004,7 @@
spin_lock_init(&mdsc->snap_flush_lock);
mdsc->cap_flush_seq = 0;
INIT_LIST_HEAD(&mdsc->cap_dirty);
+ INIT_LIST_HEAD(&mdsc->cap_dirty_migrating);
mdsc->num_cap_flushing = 0;
spin_lock_init(&mdsc->cap_dirty_lock);
init_waitqueue_head(&mdsc->cap_flushing_wq);
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 4e3a9cc..7d8a0d6 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -278,6 +278,7 @@
u64 cap_flush_seq;
struct list_head cap_dirty; /* inodes with dirty caps */
+ struct list_head cap_dirty_migrating; /* ...that are migration... */
int num_cap_flushing; /* # caps we are flushing */
spinlock_t cap_dirty_lock; /* protects above items */
wait_queue_head_t cap_flushing_wq;