Commit:     b790c3b7c38aae28c497bb363a6fe72f7c96568f
Parent:     8fd3a98f2c22982aff4d29e4ee72959d3032c123
Author:     David Teigland <[EMAIL PROTECTED]>
AuthorDate: Wed Jan 24 10:21:33 2007 -0600
Committer:  Steven Whitehouse <[EMAIL PROTECTED]>
CommitDate: Mon Feb 5 13:37:50 2007 -0500

    [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 <[EMAIL PROTECTED]>
    Signed-off-by: Steven Whitehouse <[EMAIL PROTECTED]>
 fs/dlm/lock.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

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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