[pnfs] [PATCH 9/9] pnfs client prevent race in sequence slot

[William A. (Andy) Adamson]

On 9/26/07, Benny Halevy <bhalevy at panasas.com> wrote:
>
> Hmm Andy,
>
> Actually I'm not quite sure I understand the bug and your solution...
> What prevents sequence->list.next from changing after sequence->lock is
> released?
> Similar to what could have happened before you moved the lock, in the goto
> out path...


yeah, I think I just changed the timing. I'm looking at it futher.

-->Andy

Benny
>
>
> Benny Halevy wrote:
> > andros at umich.edu wrote:
> >> From: Andy Adamson <andros at umich.edu>
> >>
> >> Move the lock to cover reading the sequence list in rpc_sequence
> >> which allowed multiple rpc's to be in flight with the same slot
> >> sequence id.
> >>
> >> Signed-off by: Andy Adamson<andros at umich.edu>
> >> ---
> >>  fs/nfs/nfs4state.c |    4 ++--
> >>  1 files changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
> >> index 4963454..cbc08af 100644
> >> --- a/fs/nfs/nfs4state.c
> >> +++ b/fs/nfs/nfs4state.c
> >> @@ -773,15 +773,15 @@ int nfs_wait_on_sequence(struct nfs_seqid *seqid,
> struct rpc_task *task)
> >>      struct rpc_sequence *sequence = seqid->sequence->sequence;
> >>      int status = 0;
> >>
> >> +    spin_lock(&sequence->lock);
> >>      if (sequence->list.next == &seqid->list)
> >>              goto out;
> >
> > This statement can be removed now as its else case is
> > handled right below. see patch below.
> >
> >> -    spin_lock(&sequence->lock);
> >>      if (sequence->list.next != &seqid->list) {
> >>              rpc_sleep_on(&sequence->wait, task, NULL, NULL);
> >>              status = -EAGAIN;
> >>      }
> >> -    spin_unlock(&sequence->lock);
> >>  out:
> >> +    spin_unlock(&sequence->lock);
> >>      return status;
> >>  }
> >>
> >
> > diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
> > index cbc08af..5cbdbc0 100644
> > --- a/fs/nfs/nfs4state.c
> > +++ b/fs/nfs/nfs4state.c
> > @@ -774,13 +774,10 @@ int nfs_wait_on_sequence(struct nfs_seqid *seqid,
> struct rpc_task *task)
> >         int status = 0;
> >
> >         spin_lock(&sequence->lock);
> > -       if (sequence->list.next == &seqid->list)
> > -               goto out;
> >         if (sequence->list.next != &seqid->list) {
> >                 rpc_sleep_on(&sequence->wait, task, NULL, NULL);
> >                 status = -EAGAIN;
> >         }
> > -out:
> >         spin_unlock(&sequence->lock);
> >         return status;
> >  }
> > --
> >
> > _______________________________________________
> > pNFS mailing list
> > pNFS at linux-nfs.org
> > http://linux-nfs.org/cgi-bin/mailman/listinfo/pnfs
>
>
>
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