From: Alexander Aring <aahringo@redhat.com>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: gfs2 <gfs2@lists.linux.dev>,
teigland@redhat.com, mark@fasheh.com, jlbec@evilplan.org,
joseph.qi@linux.alibaba.com, ocfs2-devel@lists.linux.dev
Subject: Re: [PATCHv3 v6.5-rc2 2/3] fs: dlm: allow to F_SETLKW getting interrupted
Date: Mon, 25 Mar 2024 20:32:10 -0400 [thread overview]
Message-ID: <CAK-6q+h8nUXKX0ecFXeHxc5BPONXrtfD+sOGcDgaWWuvWobTEQ@mail.gmail.com> (raw)
In-Reply-To: <CAHc6FU7LBm6RSk_M8BqZRz0LOCmDORKj0bBWSmDjM=3_iB8guQ@mail.gmail.com>
Hi,
On Mon, Mar 25, 2024 at 11:09 AM Andreas Gruenbacher
<agruenba@redhat.com> wrote:
>
> On Tue, Jul 18, 2023 at 8:07 PM Alexander Aring <aahringo@redhat.com> wrote:
> > This patch implements dlm plock F_SETLKW interruption feature. If a
> > blocking posix lock request got interrupted in user space by a signal a
> > cancellation request for a non granted lock request to the user space
> > lock manager will be send. The user lock manager answers either with
> > zero or a negative errno code. A errno of -ENOENT signals that there is
> > currently no blocking lock request waiting to being granted. In case of
> > -ENOENT it was probably to late to request a cancellation and the
> > pending lock got granted. In any error case we will wait until the lock
> > is being granted as cancellation failed, this causes also that in case
> > of an older user lock manager returning -EINVAL we will wait as
> > cancellation is not supported which should be fine. If a user requires
> > this feature the user should update dlm user space to support lock
> > request cancellation.
> >
> > Signed-off-by: Alexander Aring <aahringo@redhat.com>
> > ---
> > fs/dlm/plock.c | 56 ++++++++++++++++++++++------------
> > include/uapi/linux/dlm_plock.h | 1 +
> > 2 files changed, 37 insertions(+), 20 deletions(-)
> >
> > diff --git a/fs/dlm/plock.c b/fs/dlm/plock.c
> > index a34f605d8505..a8ffa0760913 100644
> > --- a/fs/dlm/plock.c
> > +++ b/fs/dlm/plock.c
> > @@ -74,30 +74,26 @@ static void send_op(struct plock_op *op)
> > wake_up(&send_wq);
> > }
> >
> > -/* If a process was killed while waiting for the only plock on a file,
> > - locks_remove_posix will not see any lock on the file so it won't
> > - send an unlock-close to us to pass on to userspace to clean up the
> > - abandoned waiter. So, we have to insert the unlock-close when the
> > - lock call is interrupted. */
> > -
> > -static void do_unlock_close(const struct dlm_plock_info *info)
> > +static int do_lock_cancel(const struct dlm_plock_info *orig_info)
> > {
> > struct plock_op *op;
> > + int rv;
> >
> > op = kzalloc(sizeof(*op), GFP_NOFS);
> > if (!op)
> > - return;
> > + return -ENOMEM;
> > +
> > + op->info = *orig_info;
> > + op->info.optype = DLM_PLOCK_OP_CANCEL;
> > + op->info.wait = 0;
> >
> > - op->info.optype = DLM_PLOCK_OP_UNLOCK;
> > - op->info.pid = info->pid;
> > - op->info.fsid = info->fsid;
> > - op->info.number = info->number;
> > - op->info.start = 0;
> > - op->info.end = OFFSET_MAX;
> > - op->info.owner = info->owner;
> > -
> > - op->info.flags |= DLM_PLOCK_FL_CLOSE;
> > send_op(op);
> > + wait_event(recv_wq, (op->done != 0));
> > +
> > + rv = op->info.rv;
> > +
> > + dlm_release_plock_op(op);
> > + return rv;
> > }
> >
> > int dlm_posix_lock(dlm_lockspace_t *lockspace, u64 number, struct file *file,
> > @@ -156,7 +152,7 @@ int dlm_posix_lock(dlm_lockspace_t *lockspace, u64 number, struct file *file,
> > send_op(op);
> >
> > if (op->info.wait) {
> > - rv = wait_event_killable(recv_wq, (op->done != 0));
> > + rv = wait_event_interruptible(recv_wq, (op->done != 0));
>
> It seems that this patch leads to an unnecessary change in behavior
> when a fatal signal is received (fatal_signal_pending()): before, the
> process would terminate. Now, it will try to cancel the lock, and when
> that fails, the process will keep waiting. In case of a fatal signal,
> can we skip the cancelling and do what we did before?
From my understanding interruptible() "reacts" on everything that is
also killable() and returns -ERESTARTSYS on "fatal signal". I even
tested it because wait_event_killable() has an issue, see reproducer
[0]. The issue was that it cleans too many waiters, the other waiter
of child in F_SETLKW was also cleared and it will never get a result
back from dlm_controld. I fixed that with an additional check on pid
in [1], but I have no idea about other side effects that could have
occurred as FL_CLOSE is also being used on other parts in the DLM
plock handling.
I rechecked the behaviour with the cancellation feature and sent
SIGKILL and the issue was gone without changing anything in user
space. The only thing I see why it would not have the old behaviour
(killable - that having the mentioned issue above) is that the
dlm_controld version is too old. To not run into this known issue we
just do a wait_event() that does not have those issues.
The mentioned "cancellation fails" - is not that it failed to cancel
the lock, there is some unexpected behaviour of dlm_controld, only
then we do wait_event() e.g. when we receive -EINVAL because
dlm_controld does not understand the op.
- Alex
[0] https://gitlab.com/netcoder/ltp/-/blob/dlm_fcntl_owner_testcase/testcases/kernel/syscalls/fcntl/fcntl44.c
[1] https://pagure.io/dlm/blob/main/f/dlm_controld/plock.c#_655
next prev parent reply other threads:[~2024-03-26 0:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20230718180721.745569-1-aahringo@redhat.com>
[not found] ` <20230718180721.745569-3-aahringo@redhat.com>
2024-03-25 15:08 ` [PATCHv3 v6.5-rc2 2/3] fs: dlm: allow to F_SETLKW getting interrupted Andreas Gruenbacher
2024-03-26 0:32 ` Alexander Aring [this message]
2024-03-26 11:31 ` Andreas Gruenbacher
2024-03-26 13:02 ` Alexander Aring
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