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author | David Teigland <teigland@redhat.com> | 2007-01-24 10:21:33 -0600 |
---|---|---|
committer | Steven Whitehouse <swhiteho@redhat.com> | 2007-02-05 13:37:50 -0500 |
commit | b790c3b7c38aae28c497bb363a6fe72f7c96568f (patch) | |
tree | e4dda1c5c775b4ae164a997f1216147066de31e3 | |
parent | 8fd3a98f2c22982aff4d29e4ee72959d3032c123 (diff) | |
download | linux-b790c3b7c38aae28c497bb363a6fe72f7c96568f.tar.bz2 |
[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
recover_waiters_post().
- 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 <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
-rw-r--r-- | 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 7c7ac2aaa8b1..c10257f10b90 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) mutex_unlock(&ls->ls_waiters_mutex); } +/* 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; list_del(&lkb->lkb_wait_reply); unhold_lkb(lkb); out: |