We always calling hold_lkb(lkb) if we increment lkb->lkb_wait_count. As conclusion we always need to call unhold_lkb(lkb) if we decrement lkb->lkb_wait_count. This patch will add missing unhold_lkb(lkb) if we decrement lkb->lkb_wait_count. In case of setting lkb->lkb_wait_count to zero we need to countdown until reaching zero and call unhold_lkb(lkb). The waiters list unhold_lkb(lkb) can be removed because it's done for the last lkb_wait_count decrement iteration as it's done in _remove_from_waiters().

This issue was discovered by a dlm gfs2 test case which use excessively dlm_unlock(LKF_CANCEL) feature. Probably the lkb->lkb_wait_count value never reached above 1 if this feature isn't used and so it was not discovered before.

The testcase ended in a rsb on the rsb keep data structure with a refcount of 1 but no lkb was associated with it anymore which is itself an invalid behaviour. As sideeffect it was observed that the dlm lockspace was in a kind of deadlock state by sending remove messages in a looping behaviour. With this patch I never observed a similar behaviour again.

Cc: stable@vger.kernel.org Signed-off-by: Alexander Aring aahringo@redhat.com --- fs/dlm/lock.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/dlm/lock.c b/fs/dlm/lock.c index 1899bb266e2e..d19cfa03c9bb 100644 --- a/fs/dlm/lock.c +++ b/fs/dlm/lock.c @@ -1578,6 +1578,7 @@ static int _remove_from_waiters(struct dlm_lkb *lkb, int mstype, lkb->lkb_wait_type = 0; lkb->lkb_flags &= ~DLM_IFL_OVERLAP_CANCEL; lkb->lkb_wait_count--; + unhold_lkb(lkb); goto out_del; }

@@ -1604,6 +1605,7 @@ static int _remove_from_waiters(struct dlm_lkb *lkb, int mstype, log_error(ls, "remwait error %x reply %d wait_type %d overlap", lkb->lkb_id, mstype, lkb->lkb_wait_type); lkb->lkb_wait_count--; + unhold_lkb(lkb); lkb->lkb_wait_type = 0; }

@@ -5364,11 +5366,16 @@ int dlm_recover_waiters_post(struct dlm_ls *ls) lkb->lkb_flags &= ~DLM_IFL_OVERLAP_UNLOCK; lkb->lkb_flags &= ~DLM_IFL_OVERLAP_CANCEL; lkb->lkb_wait_type = 0; - lkb->lkb_wait_count = 0; + /* drop all wait_count references we still + * hold a reference for this iteration. + */ + while (lkb->lkb_wait_count) { + lkb->lkb_wait_count--; + unhold_lkb(lkb); + } mutex_lock(&ls->ls_waiters_mutex); list_del_init(&lkb->lkb_wait_reply); mutex_unlock(&ls->ls_waiters_mutex); - unhold_lkb(lkb); /* for waiters list */

if (oc || ou) { /* do an unlock or cancel instead of resending */