[Ocfs2-devel] [PATCH] ocfs2: dlmlock_master should return DLM_NORMAL after adding lock to blocked list

[Sunil Mushran]

Acked-by: Sunil Mushran <sunil.mushran at gmail.com>


On Fri, Jun 28, 2013 at 1:47 PM, Andrew Morton <akpm at linux-foundation.org>wrote:

> On Sun, 23 Jun 2013 18:39:16 +0800 Jeff Liu <jeff.liu at oracle.com> wrote:
>
> > Hi Jiufei,
> >
> > On 06/20/2013 07:13 PM, Xue jiufei wrote:
> >
> > > Function dlmlock_master() returns DLM_RECOVERING/DLM_MIGRATING/
> > > DLM_FORWAR after adding lock to blocked list if lockres has the state
> > > DLM_LOCK_RES_RECOVERING/DLM_LOCK_RES_MIGRATING/
> > > DLM_LOCK_RES_IN_PROGRESS. so it will retry in dlmlock(). And this may
> > > cause dlm_thread fall into an infinite loop
> > >
> > >     Thread1                                  dlm_thread
> > > calls dlm_lock->dlmlock_master,
> > > if lockresA is in state
> > > DLM_LOCK_RES_RECOVERING, calls
> > > __dlm_wait_on_lockres() and waits
> > > until others threads clear this
> > > state;
> > >
> > > If cannot grant this lock,
> > > adding lock to blocked list,
> > > and return DLM_RECOVERING;
> > >
> > >                                         Grant this lock and move it to
> > >                                         grant list;
> > >
> > > After a while, retry and
> > > calls list_add_tail(), adding lock
> > > to blocked list again.
> > >
> > > Granted and blocked list of this lockres will become the following
> > > conditions:
> > >     lock_res->granted.next = dlm_lock->list_head;
> > >     lock_res->blocked.next = dlm_lock->list_head;
> > >     dlm_lock->list_head.next = dlm_lock_resource->blocked;
> > > When dlm_thread traverses the granted list, it will fall into an
> > > endless loop, checking dlm_lock.list_head, dlm_lock->list_head.next
> > > (i.e.lock_res->blocked), lock_res->blocked.next(i.e.dlm_lock.list_head
> > > again) .....
> >
> > Thanks for your nice description of this problem and this fix looks good.
> > Let's waiting for an ACK from either Sunil, Mark or Joel.
>
> Still waiting ;)
>
>
> From: Xue jiufei <xuejiufei at huawei.com>
> Subject: ocfs2: dlmlock_master() should return DLM_NORMAL after adding
> lock to blocked list
>
> dlmlock_master() returns DLM_RECOVERING/DLM_MIGRATING/ DLM_FORWAR after
> adding lock to blocked list if lockres has the state
> DLM_LOCK_RES_RECOVERING/DLM_LOCK_RES_MIGRATING/ DLM_LOCK_RES_IN_PROGRESS.
> so it will retry in dlmlock().  And this may cause dlm_thread fall into an
> infinite loop
>
>         Thread1                                  dlm_thread
> calls dlm_lock->dlmlock_master,
> if lockresA is in state
> DLM_LOCK_RES_RECOVERING, calls
> __dlm_wait_on_lockres() and waits
> until others threads clear this
> state;
>
> If cannot grant this lock,
> adding lock to blocked list,
> and return DLM_RECOVERING;
>
>                                         Grant this lock and move it to
>                                         grant list;
>
> After a while, retry and
> calls list_add_tail(), adding lock
> to blocked list again.
>
> Granted and blocked list of this lockres will become the following
> conditions:
>
>     lock_res->granted.next = dlm_lock->list_head;
>     lock_res->blocked.next = dlm_lock->list_head;
>     dlm_lock->list_head.next = dlm_lock_resource->blocked;
>
> When dlm_thread traverses the granted list, it will fall into an endless
> loop, checking dlm_lock.list_head, dlm_lock->list_head.next
> (i.e.lock_res->blocked), lock_res->blocked.next(i.e.dlm_lock.list_head
> again) .....
>
> Signed-off-by: joyce <xuejiufei at huawei.com>
> Reviewed-by: jensen <shencanquan at huawei.com>
> Cc: Jeff Liu <jeff.liu at oracle.com>
> Cc: Sunil Mushran <sunil.mushran at gmail.com>
> Cc: Mark Fasheh <mfasheh at suse.com>
> Cc: Joel Becker <jlbec at evilplan.org>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> ---
>
>  fs/ocfs2/dlm/dlmlock.c |    1 +
>  1 file changed, 1 insertion(+)
>
> diff -puN
> fs/ocfs2/dlm/dlmlock.c~ocfs2-dlmlock_master-should-return-dlm_normal-after-adding-lock-to-blocked-list
> fs/ocfs2/dlm/dlmlock.c
> ---
> a/fs/ocfs2/dlm/dlmlock.c~ocfs2-dlmlock_master-should-return-dlm_normal-after-adding-lock-to-blocked-list
> +++ a/fs/ocfs2/dlm/dlmlock.c
> @@ -178,6 +178,7 @@ static enum dlm_status dlmlock_master(st
>                                      lock->ml.node);
>                         }
>                 } else {
> +                       status = DLM_NORMAL;
>                         dlm_lock_get(lock);
>                         list_add_tail(&lock->list, &res->blocked);
>                         kick_thread = 1;
> _
>
>
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