[Ocfs2-devel] ocfs2: A race about mle is unlinked and freed for the dead node, BUG

[Zhangguanghui]

Hi All,

when the mle have been used in dlm_get_lock_resouce, other nodes dead at the same time,
the mle that is block type may be unlinked and freed repeatedly for dead nodes.
so it is a BUG  about mle->mle_refs.refcount in __dlm_put_mle  in dlm_get_lock_resouce.
Finally, any feedback about this process (positive or negative) would be  greatly appreciated.

*** linux-4.1.35/fs/ocfs2/dlm/dlmmaster.c 2016-11-09 17:39:02.230163503 +0800
--- dlmmaster.c.update 2016-11-09 17:41:39.210166752 +0800
***************
*** 3229,3248 ****
--- 3229,3261 ----
struct dlm_master_list_entry *mle, u8 dead_node)
{
int bit;
+ int next_bit = O2NM_MAX_NODES;
BUG_ON(mle->type != DLM_MLE_BLOCK);

spin_lock(&mle->spinlock);
bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, 0);
+ if (bit != O2NM_MAX_NODES)
+ next_bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, bit+1);
+
if (bit != dead_node) {
mlog(0, "mle found, but dead node %u would not have been "
"master\n", dead_node);
spin_unlock(&mle->spinlock);
+ } else if (mle->inuse && next_bit != O2NM_MAX_NODES) {
+ /*Ignore it, the mle is used, other nodes dead now.
+ *as it is unlinked and freed for the dead node, it's a BUG*/
+ mlog(ML_ERROR, "the mle is used, but inuse %d, dead node %u, "
+ "master %u\n", mle->inuse, dead_node, mle->master);
+ clear_bit(bit, mle->maybe_map);
+ spin_unlock(&mle->spinlock);
+
} else {
/* Must drop the refcount by one since the assert_master will
* never arrive. This may result in the mle being unlinked and
* freed, but there may still be a process waiting in the
* dlmlock path which is fine. */
mlog(0, "node %u was expected master\n", dead_node);
+ clear_bit(bit, mle->maybe_map);
atomic_set(&mle->woken, 1);
spin_unlock(&mle->spinlock);
wake_up(&mle->wq);

________________________________
All the best wishes for you.
zhangguanghui

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