ceph: fix flush_dirty_caps race with caps migration

The flush_dirty_caps() used to loop over the first entry of the cap_dirty
dirty list on the assumption that after calling ceph_check_caps() it would
be removed from the list.  This isn't true for caps that are being
migrated between MDSs, where we've received the EXPORT but not the IMPORT.

Instead, do a safe list iteration, and pin the next inode on the list via
the CEPH_I_NOFLUSH flag.

Signed-off-by: Sage Weil <sage@newdream.net>

2 files changed, 39 insertions, 7 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 295b7e547a3..8b89b912325 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1573,6 +1573,11 @@ retry_locked:
                 }
 
 ack:
+                if (ci->i_ceph_flags & CEPH_I_NOFLUSH) {
+                        dout(" skipping %p I_NOFLUSH set\n", inode);
+                        continue;
+                }
+
                 if (session && session != cap->session) {
                         dout("oops, wrong session %p mutex\n", session);
                         mutex_unlock(&session->s_mutex);
@@ -1652,6 +1657,10 @@ static int try_flush_caps(struct inode *inode, struct ceph_mds_session *session,
 
 retry:
         spin_lock(&inode->i_lock);
+        if (ci->i_ceph_flags & CEPH_I_NOFLUSH) {
+                dout("try_flush_caps skipping %p I_NOFLUSH set\n", inode);
+                goto out;
+        }
         if (ci->i_dirty_caps && ci->i_auth_cap) {
                 struct ceph_cap *cap = ci->i_auth_cap;
                 int used = __ceph_caps_used(ci);
@@ -2747,16 +2756,38 @@ void ceph_check_delayed_caps(struct ceph_mds_client *mdsc)
  */
 void ceph_flush_dirty_caps(struct ceph_mds_client *mdsc)
 {
-        struct ceph_inode_info *ci;
-        struct inode *inode;
+        struct ceph_inode_info *ci, *nci = NULL;
+        struct inode *inode, *ninode = NULL;
+        struct list_head *p, *n;
 
         dout("flush_dirty_caps\n");
         spin_lock(&mdsc->cap_dirty_lock);
-        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);
+        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;
+                }
                 spin_unlock(&mdsc->cap_dirty_lock);
                 if (inode) {
                         ceph_check_caps(ci, CHECK_CAPS_NODELAY|CHECK_CAPS_FLUSH,
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index ff7aaa32736..6a778f2c3f6 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -289,6 +289,7 @@ struct ceph_inode_xattrs_info {
 #define CEPH_I_COMPLETE  1  /* we have complete directory cached */
 #define CEPH_I_NODELAY   4  /* do not delay cap release */
 #define CEPH_I_FLUSH     8  /* do not delay flush of dirty metadata */
+#define CEPH_I_NOFLUSH  16  /* do not flush dirty caps */
 
 struct ceph_inode_info {
         struct ceph_vino i_vino;   /* ceph ino + snap */