[3.8.y.z extended stable] Patch "ocfs2: dlm: fix lock migration crash" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ocfs2: dlm: fix lock migration crash

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 90ccc306cf0b6fe8d93da7d13c75ef176cf7dae1 Mon Sep 17 00:00:00 2001
From: Junxiao Bi <junxiao.bi at oracle.com>
Date: Thu, 3 Apr 2014 14:46:49 -0700
Subject: ocfs2: dlm: fix lock migration crash

commit 34aa8dac482f1358d59110d5e3a12f4351f6acaa upstream.

This issue was introduced by commit 800deef3f6f8 ("ocfs2: use
list_for_each_entry where benefical") in 2007 where it replaced
list_for_each with list_for_each_entry.  The variable "lock" will point
to invalid data if "tmpq" list is empty and a panic will be triggered
due to this.  Sunil advised reverting it back, but the old version was
also not right.  At the end of the outer for loop, that
list_for_each_entry will also set "lock" to an invalid data, then in the
next loop, if the "tmpq" list is empty, "lock" will be an stale invalid
data and cause the panic.  So reverting the list_for_each back and reset
"lock" to NULL to fix this issue.

Another concern is that this seemes can not happen because the "tmpq"
list should not be empty.  Let me describe how.

old lock resource owner(node 1):                                  migratation target(node 2):
image there's lockres with a EX lock from node 2 in
granted list, a NR lock from node x with convert_type
EX in converting list.
dlm_empty_lockres() {
 dlm_pick_migration_target() {
   pick node 2 as target as its lock is the first one
   in granted list.
 }
 dlm_migrate_lockres() {
   dlm_mark_lockres_migrating() {
     res->state |= DLM_LOCK_RES_BLOCK_DIRTY;
     wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
	 //after the above code, we can not dirty lockres any more,
     // so dlm_thread shuffle list will not run
                                                                   downconvert lock from EX to NR
                                                                   upconvert lock from NR to EX
<<< migration may schedule out here, then
<<< node 2 send down convert request to convert type from EX to
<<< NR, then send up convert request to convert type from NR to
<<< EX, at this time, lockres granted list is empty, and two locks
<<< in the converting list, node x up convert lock followed by
<<< node 2 up convert lock.

	 // will set lockres RES_MIGRATING flag, the following
	 // lock/unlock can not run
     dlm_lockres_release_ast(dlm, res);
   }

   dlm_send_one_lockres()
                                                                 dlm_process_recovery_data()
                                                                   for (i=0; i<mres->num_locks; i++)
                                                                     if (ml->node == dlm->node_num)
                                                                       for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
                                                                        list_for_each_entry(lock, tmpq, list)
                                                                        if (lock) break; <<< lock is invalid as grant list is empty.
                                                                       }
                                                                       if (lock->ml.node != ml->node)
                                                                         BUG() >>> crash here
 }

I see the above locks status from a vmcore of our internal bug.

Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
Reviewed-by: Wengang Wang <wen.gang.wang at oracle.com>
Cc: Sunil Mushran <sunil.mushran at gmail.com>
Reviewed-by: Srinivas Eeda <srinivas.eeda at oracle.com>
Cc: Joel Becker <jlbec at evilplan.org>
Cc: Mark Fasheh <mfasheh at suse.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/ocfs2/dlm/dlmrecovery.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index 01ebfd0..df3cfd3 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -1752,13 +1752,13 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
 				     struct dlm_migratable_lockres *mres)
 {
 	struct dlm_migratable_lock *ml;
-	struct list_head *queue;
+	struct list_head *queue, *iter;
 	struct list_head *tmpq = NULL;
 	struct dlm_lock *newlock = NULL;
 	struct dlm_lockstatus *lksb = NULL;
 	int ret = 0;
 	int i, j, bad;
-	struct dlm_lock *lock = NULL;
+	struct dlm_lock *lock;
 	u8 from = O2NM_MAX_NODES;
 	unsigned int added = 0;
 	__be64 c;
@@ -1793,14 +1793,16 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
 			/* MIGRATION ONLY! */
 			BUG_ON(!(mres->flags & DLM_MRES_MIGRATION));

+			lock = NULL;
 			spin_lock(&res->spinlock);
 			for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
 				tmpq = dlm_list_idx_to_ptr(res, j);
-				list_for_each_entry(lock, tmpq, list) {
-					if (lock->ml.cookie != ml->cookie)
-						lock = NULL;
-					else
+				list_for_each(iter, tmpq) {
+					lock = list_entry(iter,
+						  struct dlm_lock, list);
+					if (lock->ml.cookie == ml->cookie)
 						break;
+					lock = NULL;
 				}
 				if (lock)
 					break;
--
1.9.1