From: David Teigland <teigland@redhat.com> Subject: [RHEL5.1 PATCH] dlm: can miss clearing resend flag Date: Thu, 25 Jan 2007 09:19:56 -0600 Bugzilla: 223522 Message-Id: <20070125151956.GG21980@redhat.com> Changelog: [dlm] can miss clearing resend flag bz 223522 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. patch is in upstream gfs2 git tree Index: linux-rhel5-quilt/fs/dlm/lock.c =================================================================== --- linux-rhel5-quilt.orig/fs/dlm/lock.c 2007-01-24 15:04:12.000000000 -0600 +++ linux-rhel5-quilt/fs/dlm/lock.c 2007-01-24 15:04:38.000000000 -0600 @@ -754,6 +754,11 @@ 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 @@ goto out; } lkb->lkb_wait_type = 0; + lkb->lkb_flags &= ~DLM_IFL_RESEND; list_del(&lkb->lkb_wait_reply); unhold_lkb(lkb); out: