From: Leon Romanovsky <leon@kernel.org>
To: Doug Ledford <dledford@redhat.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>,
RDMA mailing list <linux-rdma@vger.kernel.org>,
Saeed Mahameed <saeedm@mellanox.com>
Subject: Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister
Date: Thu, 1 Aug 2019 19:23:56 +0300 [thread overview]
Message-ID: <20190801162356.GV4832@mtr-leonro.mtl.com> (raw)
In-Reply-To: <a0dc81b63fdef1b7e877d5172be13792dda763d2.camel@redhat.com>
On Thu, Aug 01, 2019 at 12:11:20PM -0400, Doug Ledford wrote:
> On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > > There's no need for a lockdep. The removal of the notifier callback
> > > entry is re-entrant safe. The core removal routines have their own
> > > spinlock they use to protect the actual notifier list. If you call
> > > it
> > > more than once, the second and subsequent calls merely scan the
> > > list,
> > > find no matching entry, and return ENOENT. The only reason this
> > > might
> > > need a lock and a lockdep entry is if you are protecting against a
> > > race
> > > with the *add* notifier code in the mlx5 driver specifically (the
> > > core
> > > add code won't have an issue, but since you only have a single place
> > > to
> > > store the notifier callback pointer, if it would be possible for you
> > > to
> > > add two callbacks and write over the first callback pointer with the
> > > second without removing the first, then you would leak a callback
> > > notifier in the core notifier list).
> >
> > atomic_notifier_chain_unregister() unconditionally calls to
> > syncronize_rcu() and I'm not so sure that it is best thing to do
> > for every port unbind.
> >
> > Actually, I'm completely lost here, we are all agree that the patch
> > fixes issue correctly, and it returns the code to be exactly as
> > it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> > notifier
> > API"). Can we simply merge it and fix the kernel panic?
>
> As long as you are OK with me adding a comment to the patch so people
> coming back later won't scratch their head about how can it possible be
> right to do that sequence without a lock held, I'm fine merging the fix.
>
> Something like:
>
> /*
> * The check/unregister/set-NULL sequence below does not need to be
> * locked for correctness as it's only an optimization, and can't
> * be under a lock or will throw a scheduling while atomic error.
> */
I think that the best place will be in commit message for this explanation,
but I'm fine with the comment inside code as well.
Thanks a lot, I appreciate it.
>
> --
> Doug Ledford <dledford@redhat.com>
> GPG KeyID: B826A3330E572FDD
> Fingerprint = AE6B 1BDA 122B 23B4 265B 1274 B826 A333 0E57 2FDD
next prev parent reply other threads:[~2019-08-01 16:24 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-31 8:38 [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister Leon Romanovsky
2019-07-31 16:22 ` Doug Ledford
2019-07-31 17:00 ` Jason Gunthorpe
2019-07-31 17:09 ` Leon Romanovsky
2019-07-31 17:22 ` Jason Gunthorpe
2019-07-31 18:01 ` Leon Romanovsky
2019-07-31 18:51 ` Doug Ledford
2019-08-01 8:22 ` Leon Romanovsky
2019-07-31 19:55 ` Jason Gunthorpe
2019-08-01 8:27 ` Leon Romanovsky
2019-08-01 12:00 ` Jason Gunthorpe
2019-08-01 12:08 ` Leon Romanovsky
2019-08-01 14:16 ` Doug Ledford
2019-08-01 15:59 ` Leon Romanovsky
2019-08-01 16:11 ` Doug Ledford
2019-08-01 16:20 ` Jason Gunthorpe
2019-08-01 16:40 ` Doug Ledford
2019-08-01 16:43 ` Jason Gunthorpe
2019-08-01 16:50 ` Doug Ledford
2019-08-01 17:31 ` Leon Romanovsky
2019-08-01 16:23 ` Leon Romanovsky [this message]
2019-08-01 16:42 ` Doug Ledford
2019-08-01 17:33 ` Leon Romanovsky
2019-08-01 20:09 ` Doug Ledford
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190801162356.GV4832@mtr-leonro.mtl.com \
--to=leon@kernel.org \
--cc=dledford@redhat.com \
--cc=jgg@mellanox.com \
--cc=linux-rdma@vger.kernel.org \
--cc=saeedm@mellanox.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).