ceph: avoid iput_final() while holding mutex or in dispatch thread

iput_final() may wait for reahahead pages. The wait can cause deadlock.
For example:

  Workqueue: ceph-msgr ceph_con_workfn [libceph]
    Call Trace:
     schedule+0x36/0x80
     io_schedule+0x16/0x40
     __lock_page+0x101/0x140
     truncate_inode_pages_range+0x556/0x9f0
     truncate_inode_pages_final+0x4d/0x60
     evict+0x182/0x1a0
     iput+0x1d2/0x220
     iterate_session_caps+0x82/0x230 [ceph]
     dispatch+0x678/0xa80 [ceph]
     ceph_con_workfn+0x95b/0x1560 [libceph]
     process_one_work+0x14d/0x410
     worker_thread+0x4b/0x460
     kthread+0x105/0x140
     ret_from_fork+0x22/0x40

  Workqueue: ceph-msgr ceph_con_workfn [libceph]
    Call Trace:
     __schedule+0x3d6/0x8b0
     schedule+0x36/0x80
     schedule_preempt_disabled+0xe/0x10
     mutex_lock+0x2f/0x40
     ceph_check_caps+0x505/0xa80 [ceph]
     ceph_put_wrbuffer_cap_refs+0x1e5/0x2c0 [ceph]
     writepages_finish+0x2d3/0x410 [ceph]
     __complete_request+0x26/0x60 [libceph]
     handle_reply+0x6c8/0xa10 [libceph]
     dispatch+0x29a/0xbb0 [libceph]
     ceph_con_workfn+0x95b/0x1560 [libceph]
     process_one_work+0x14d/0x410
     worker_thread+0x4b/0x460
     kthread+0x105/0x140
     ret_from_fork+0x22/0x40

In above example, truncate_inode_pages_range() waits for readahead pages
while holding s_mutex. ceph_check_caps() waits for s_mutex and blocks
OSD dispatch thread. Later OSD replies (for readahead) can't be handled.

ceph_check_caps() also may lock snap_rwsem for read. So similar deadlock
can happen if iput_final() is called while holding snap_rwsem.

In general, it's not good to call iput_final() inside MDS/OSD dispatch
threads or while holding any mutex.

The fix is introducing ceph_async_iput(), which calls iput_final() in
workqueue.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

6 files changed, 71 insertions, 27 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 72f8e1311392..52a2b90621cd 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -2992,8 +2992,10 @@ void ceph_put_wrbuffer_cap_refs(struct ceph_inode_info *ci, int nr,
         }
         if (complete_capsnap)
                 wake_up_all(&ci->i_cap_wq);
-        while (put-- > 0)
-                iput(inode);
+        while (put-- > 0) {
+                /* avoid calling iput_final() in osd dispatch threads */
+                ceph_async_iput(inode);
+        }
 }
 
 /*
@@ -3964,8 +3966,9 @@ void ceph_handle_caps(struct ceph_mds_session *session,
 done:
         mutex_unlock(&session->s_mutex);
 done_unlocked:
-        iput(inode);
         ceph_put_string(extra_info.pool_ns);
+        /* avoid calling iput_final() in mds dispatch threads */
+        ceph_async_iput(inode);
         return;
 
 flush_cap_releases:
@@ -4011,7 +4014,8 @@ void ceph_check_delayed_caps(struct ceph_mds_client *mdsc)
                 if (inode) {
                         dout("check_delayed_caps on %p\n", inode);
                         ceph_check_caps(ci, flags, NULL);
-                        iput(inode);
+                        /* avoid calling iput_final() in tick thread */
+                        ceph_async_iput(inode);
                 }
         }
         spin_unlock(&mdsc->cap_delay_lock);
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 3acdd3cc6039..761451f36e2d 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -1476,7 +1476,8 @@ static int readdir_prepopulate_inodes_only(struct ceph_mds_request *req,
                         pr_err("fill_inode badness on %p got %d\n", in, rc);
                         err = rc;
                 }
-                iput(in);
+                /* avoid calling iput_final() in mds dispatch threads */
+                ceph_async_iput(in);
         }
 
         return err;
@@ -1674,8 +1675,11 @@ retry_lookup:
                                  &req->r_caps_reservation);
                 if (ret < 0) {
                         pr_err("fill_inode badness on %p\n", in);
-                        if (d_really_is_negative(dn))
-                                iput(in);
+                        if (d_really_is_negative(dn)) {
+                                /* avoid calling iput_final() in mds
+                                 * dispatch threads */
+                                ceph_async_iput(in);
+                        }
                         d_drop(dn);
                         err = ret;
                         goto next_item;
@@ -1685,7 +1689,7 @@ retry_lookup:
                         if (ceph_security_xattr_deadlock(in)) {
                                 dout(" skip splicing dn %p to inode %p"
                                      " (security xattr deadlock)\n", dn, in);
-                                iput(in);
+                                ceph_async_iput(in);
                                 skipped++;
                                 goto next_item;
                         }
@@ -1737,6 +1741,25 @@ bool ceph_inode_set_size(struct inode *inode, loff_t size)
 }
 
 /*
+ * Put reference to inode, but avoid calling iput_final() in current thread.
+ * iput_final() may wait for reahahead pages. The wait can cause deadlock in
+ * some contexts.
+ */
+void ceph_async_iput(struct inode *inode)
+{
+        if (!inode)
+                return;
+        for (;;) {
+                if (atomic_add_unless(&inode->i_count, -1, 1))
+                        break;
+                if (queue_work(ceph_inode_to_client(inode)->inode_wq,
+                               &ceph_inode(inode)->i_work))
+                        break;
+                /* queue work failed, i_count must be at least 2 */
+        }
+}
+
+/*
  * Write back inode data in a worker thread.  (This can't be done
  * in the message handler context.)
  */
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 959b1bf7c327..6af2d0d4a87a 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -690,11 +690,12 @@ void ceph_mdsc_release_request(struct kref *kref)
                 ceph_msg_put(req->r_reply);
         if (req->r_inode) {
                 ceph_put_cap_refs(ceph_inode(req->r_inode), CEPH_CAP_PIN);
-                iput(req->r_inode);
+                /* avoid calling iput_final() in mds dispatch threads */
+                ceph_async_iput(req->r_inode);
         }
         if (req->r_parent)
                 ceph_put_cap_refs(ceph_inode(req->r_parent), CEPH_CAP_PIN);
-        iput(req->r_target_inode);
+        ceph_async_iput(req->r_target_inode);
         if (req->r_dentry)
                 dput(req->r_dentry);
         if (req->r_old_dentry)
@@ -708,7 +709,7 @@ void ceph_mdsc_release_request(struct kref *kref)
                  */
                 ceph_put_cap_refs(ceph_inode(req->r_old_dentry_dir),
                                   CEPH_CAP_PIN);
-                iput(req->r_old_dentry_dir);
+                ceph_async_iput(req->r_old_dentry_dir);
         }
         kfree(req->r_path1);
         kfree(req->r_path2);
@@ -818,7 +819,8 @@ static void __unregister_request(struct ceph_mds_client *mdsc,
         }
 
         if (req->r_unsafe_dir) {
-                iput(req->r_unsafe_dir);
+                /* avoid calling iput_final() in mds dispatch threads */
+                ceph_async_iput(req->r_unsafe_dir);
                 req->r_unsafe_dir = NULL;
         }
 
@@ -983,7 +985,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
                 cap = rb_entry(rb_first(&ci->i_caps), struct ceph_cap, ci_node);
         if (!cap) {
                 spin_unlock(&ci->i_ceph_lock);
-                iput(inode);
+                ceph_async_iput(inode);
                 goto random;
         }
         mds = cap->session->s_mds;
@@ -992,7 +994,9 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
              cap == ci->i_auth_cap ? "auth " : "", cap);
         spin_unlock(&ci->i_ceph_lock);
 out:
-        iput(inode);
+        /* avoid calling iput_final() while holding mdsc->mutex or
+         * in mds dispatch threads */
+        ceph_async_iput(inode);
         return mds;
 
 random:
@@ -1302,7 +1306,9 @@ int ceph_iterate_session_caps(struct ceph_mds_session *session,
                 spin_unlock(&session->s_cap_lock);
 
                 if (last_inode) {
-                        iput(last_inode);
+                        /* avoid calling iput_final() while holding
+                         * s_mutex or in mds dispatch threads */
+                        ceph_async_iput(last_inode);
                         last_inode = NULL;
                 }
                 if (old_cap) {
@@ -1335,7 +1341,7 @@ out:
         session->s_cap_iterator = NULL;
         spin_unlock(&session->s_cap_lock);
 
-        iput(last_inode);
+        ceph_async_iput(last_inode);
         if (old_cap)
                 ceph_put_cap(session->s_mdsc, old_cap);
 
@@ -1471,7 +1477,8 @@ static void remove_session_caps(struct ceph_mds_session *session)
                         spin_unlock(&session->s_cap_lock);
 
                         inode = ceph_find_inode(sb, vino);
-                        iput(inode);
+                         /* avoid calling iput_final() while holding s_mutex */
+                        ceph_async_iput(inode);
 
                         spin_lock(&session->s_cap_lock);
                 }
@@ -3912,8 +3919,9 @@ release:
         ceph_con_send(&session->s_con, msg);
 
 out:
-        iput(inode);
         mutex_unlock(&session->s_mutex);
+        /* avoid calling iput_final() in mds dispatch threads */
+        ceph_async_iput(inode);
         return;
 
 bad:
diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
index c4522212872c..d629fc857450 100644
--- a/fs/ceph/quota.c
+++ b/fs/ceph/quota.c
@@ -74,7 +74,8 @@ void ceph_handle_quota(struct ceph_mds_client *mdsc,
                             le64_to_cpu(h->max_files));
         spin_unlock(&ci->i_ceph_lock);
 
-        iput(inode);
+        /* avoid calling iput_final() in dispatch thread */
+        ceph_async_iput(inode);
 }
 
 static struct ceph_quotarealm_inode *
@@ -235,7 +236,8 @@ restart:
 
                 ci = ceph_inode(in);
                 has_quota = __ceph_has_any_quota(ci);
-                iput(in);
+                /* avoid calling iput_final() while holding mdsc->snap_rwsem */
+                ceph_async_iput(in);
 
                 next = realm->parent;
                 if (has_quota || !next)
@@ -372,7 +374,8 @@ restart:
                         pr_warn("Invalid quota check op (%d)\n", op);
                         exceeded = true; /* Just break the loop */
                 }
-                iput(in);
+                /* avoid calling iput_final() while holding mdsc->snap_rwsem */
+                ceph_async_iput(in);
 
                 next = realm->parent;
                 if (exceeded || !next)
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index b26e12cd8ec3..72c6c022f02b 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -648,13 +648,15 @@ static void queue_realm_cap_snaps(struct ceph_snap_realm *realm)
                 if (!inode)
                         continue;
                 spin_unlock(&realm->inodes_with_caps_lock);
-                iput(lastinode);
+                /* avoid calling iput_final() while holding
+                 * mdsc->snap_rwsem or in mds dispatch threads */
+                ceph_async_iput(lastinode);
                 lastinode = inode;
                 ceph_queue_cap_snap(ci);
                 spin_lock(&realm->inodes_with_caps_lock);
         }
         spin_unlock(&realm->inodes_with_caps_lock);
-        iput(lastinode);
+        ceph_async_iput(lastinode);
 
         dout("queue_realm_cap_snaps %p %llx done\n", realm, realm->ino);
 }
@@ -806,7 +808,9 @@ static void flush_snaps(struct ceph_mds_client *mdsc)
                 ihold(inode);
                 spin_unlock(&mdsc->snap_flush_lock);
                 ceph_flush_snaps(ci, &session);
-                iput(inode);
+                /* avoid calling iput_final() while holding
+                 * session->s_mutex or in mds dispatch threads */
+                ceph_async_iput(inode);
                 spin_lock(&mdsc->snap_flush_lock);
         }
         spin_unlock(&mdsc->snap_flush_lock);
@@ -950,12 +954,14 @@ void ceph_handle_snap(struct ceph_mds_client *mdsc,
                         ceph_get_snap_realm(mdsc, realm);
                         ceph_put_snap_realm(mdsc, oldrealm);
 
-                        iput(inode);
+                        /* avoid calling iput_final() while holding
+                         * mdsc->snap_rwsem or mds in dispatch threads */
+                        ceph_async_iput(inode);
                         continue;
 
 skip_inode:
                         spin_unlock(&ci->i_ceph_lock);
-                        iput(inode);
+                        ceph_async_iput(inode);
                 }
 
                 /* we may have taken some of the old realm's children. */
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 3fb866a979ce..5f27e1f7f2d6 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -899,9 +899,9 @@ extern int ceph_inode_holds_cap(struct inode *inode, int mask);
 extern bool ceph_inode_set_size(struct inode *inode, loff_t size);
 extern void __ceph_do_pending_vmtruncate(struct inode *inode);
 extern void ceph_queue_vmtruncate(struct inode *inode);
-
 extern void ceph_queue_invalidate(struct inode *inode);
 extern void ceph_queue_writeback(struct inode *inode);
+extern void ceph_async_iput(struct inode *inode);
 
 extern int __ceph_do_getattr(struct inode *inode, struct page *locked_page,
                              int mask, bool force);