Hi Junxiao,
On Thu, Jan 21, 2016 at 03:10:20PM +0800, Junxiao Bi wrote:
> Hi Eric,
>
> This patch should fix your issue.
> "NFS hangs in __ocfs2_cluster_lock due to race with ocfs2_unblock_lock"
Thanks a lot for bringing up this patch! It hasn't been merged into mainline(
at least 4.4), right?
I have found this patch in maillist and it looks good! I'd like to test it right
now and give feadback!
Thanks again,
Eric
>
> Thanks,
> Junxiao.
> On 01/20/2016 12:46 AM, Eric Ren wrote:
> > This problem was introduced by commit
> > a19128260107f951d1b4c421cf98b92f8092b069.
> > OCFS2_LOCK_UPCONVERT_FINISHING is set just before clearing OCFS2_LOCK_BUSY.
> > This
> > will prevent dc thread from downconverting immediately, and let
> > mask-waiters in
> > ->l_mask_waiters list whose requesting level is compatible with ->l_level
> > to take
> > the lock. But if we have two waiters in mw list, the first is to get EX
> > lock, and
> > the second is to to get PR lock. The first may fail to get lock and then
> > clear
> > UPCONVERT_FINISHING. It's too early to clear the flag because this second
> > will be
> > also queued again even if ->l_level is PR. As a result, nobody would kick
> > up dc
> > thread, leaving dlmglue a deadlock until another lockres relative thread
> > wake it
> > up.
> >
> > More specifically, for example:
> > On node1, there is thread W1 keeping writing; on node2, there are thread R1
> > and
> > R2 keeping reading; sure this 3 threads make IO on the same shared file. At
> > a
> > time, node2 is receiving ast(0=>3), followed immediately by a bast
> > requesting EX
> > lock on behave of node1. Then this may happen:
> > node2: node1:
> > l_level==3; R1(3); R2(3) l_level==3
> > R1(unlock); R1(3=>5, update atime) W1(3=>5)
> > BAST
> > R2(unlock); AST(3=>0)
> > R2(0=>3)
> > BAST
> > AST(0=>3)
> > set OCFS2_LOCK_UPCONVERT_FINISHING
> > clear OCFS2_LOCK_BUSY
> > W1(3=>5)
> > BAST
> > dc thread requeue=yes
> > R1(clear OCFS2_LOCK_UPCONVERT_FINISHING,wait)
> > R2(wait)
> > ...
> > dlmglue deadlock util dc thread woken up by others
> >
> > This fix is to clear OCFS2_LOCK_UPCONVERT_FINISHING util OCFS2_LOCK_BUSY has
> > been cleared and every waiters has been looped.
> >
> > Signed-off-by: Eric Ren <z...@suse.com>
> > ---
> > fs/ocfs2/dlmglue.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> > index f92612e..72f8b6c 100644
> > --- a/fs/ocfs2/dlmglue.c
> > +++ b/fs/ocfs2/dlmglue.c
> > @@ -824,6 +824,8 @@ static void lockres_clear_flags(struct ocfs2_lock_res
> > *lockres,
> > unsigned long clear)
> > {
> > lockres_set_flags(lockres, lockres->l_flags & ~clear);
> > + if(clear & OCFS2_LOCK_BUSY)
> > + lockres->l_flags &= ~OCFS2_LOCK_UPCONVERT_FINISHING;
> > }
> >
> > static inline void ocfs2_generic_handle_downconvert_action(struct
> > ocfs2_lock_res *lockres)
> > @@ -1522,8 +1524,6 @@ update_holders:
> >
> > ret = 0;
> > unlock:
> > - lockres_clear_flags(lockres, OCFS2_LOCK_UPCONVERT_FINISHING);
> > -
> > spin_unlock_irqrestore(&lockres->l_lock, flags);
> > out:
> > /*
> >
>
>
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