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Subject[DLM] can miss clearing resend flag
>From 61a6511f5e603c0baadf542f632981248fdc7266 Mon Sep 17 00:00:00 2001
From: David Teigland <>
Date: Wed, 24 Jan 2007 10:21:33 -0600
Subject: [PATCH] [DLM] can miss clearing resend flag

A long, complicated sequence of events, beginning with the RESEND flag not
being cleared on an lkb, can result in an unlock never completing.

- lkb on waiters list for remote lookup
- the remote node is both the dir node and the master node, so
it optimizes the lookup into a request and sends a request
reply back
- the request reply is saved on the requestqueue to be processed
after recovery
- recovery runs dlm_recover_waiters_pre() which sets RESEND flag
so the lookup will be resent after recovery
- end of recovery: process_requestqueue takes saved request reply
which removes the lkb off the waitesr list, _without_ clearing
the RESEND flag
- end of recovery: dlm_recover_waiters_post() doesn't do anything
with the now completed lookup lkb (would usually clear RESEND)
- later, the node unmounts, unlocks this lkb that still has RESEND
flag set
- the lkb is on the waiters list again, now for unlock, when recovery
occurs, dlm_recover_waiters_pre() shows the lkb for unlock with RESEND
set, doesn't do anything since the master still exists
- end of recovery: dlm_recover_waiters_post() takes this lkb off
the waiters list because it has the RESEND flag set, then reports
an error because unlocks are never supposed to be handled in
- later, the unlock reply is received, doesn't find the lkb on
the waiters list because recover_waiters_post() has wrongly
removed it.
- the unlock operation has been lost, and we're left with a
stray granted lock
- unmount spins waiting for the unlock to complete

The visible evidence of this problem will be a node where gfs umount is
spinning, the dlm waiters list will be empty, and the dlm locks list will
show a granted lock.

The fix is simply to clear the RESEND flag when taking an lkb off the
waiters list.

Signed-off-by: David Teigland <>
Signed-off-by: Steven Whitehouse <>

diff --git a/fs/dlm/lock.c b/fs/dlm/lock.c
index 7c7ac2a..c10257f 100644
--- a/fs/dlm/lock.c
+++ b/fs/dlm/lock.c
@@ -754,6 +754,11 @@ static void add_to_waiters(struct dlm_lkb *lkb, int mstype)

+/* We clear the RESEND flag because we might be taking an lkb off the waiters
+ list as part of process_requestqueue (e.g. a lookup that has an optimized
+ request reply on the requestqueue) between dlm_recover_waiters_pre() which
+ set RESEND and dlm_recover_waiters_post() */
static int _remove_from_waiters(struct dlm_lkb *lkb)
int error = 0;
@@ -764,6 +769,7 @@ static int _remove_from_waiters(struct dlm_lkb *lkb)
goto out;
lkb->lkb_wait_type = 0;
+ lkb->lkb_flags &= ~DLM_IFL_RESEND;

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