From: Sagi Grimberg <sagi@grimberg.me>
To: Christoph Hellwig <hch@infradead.org>, Hannes Reinecke <hare@suse.de>
Cc: Daniel Wagner <dwagner@suse.de>,
linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
Keith Busch <kbusch@kernel.org>
Subject: Re: [PATCH v1] nvme: avoid race in shutdown namespace removal
Date: Wed, 1 Sep 2021 17:41:57 +0300 [thread overview]
Message-ID: <7677d695-aa57-ee91-3b32-65570cefdff4@grimberg.me> (raw)
In-Reply-To: <YS+AYA+5/o8Qj08Q@infradead.org>
>> Most likely. Do drop me a mail on how to create a reproducer for that; it's
>> not exactly trivial as you need to patch qemu for that
>> (and, of course, those patches will not go upstream as they again hit a
>> section which the maintainer deemed to be reworked any time now. So of
>> course he can't possibly apply them.)
>> (I seem to have a particular spell of bad luck, seeing that it's the _third_
>> time this happened to me :-( )
>
> Soo. What is the problem in simply checking in nvme_find_ns_head that
> h->list is non-empty? E.g. this variant of the patch from Daniel:
Don't see why this won't work...
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index d535b00d65816..ce91655fa29bb 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3523,7 +3523,9 @@ static struct nvme_ns_head *nvme_find_ns_head(struct nvme_subsystem *subsys,
> lockdep_assert_held(&subsys->lock);
>
> list_for_each_entry(h, &subsys->nsheads, entry) {
> - if (h->ns_id == nsid && nvme_tryget_ns_head(h))
> + if (h->ns_id != nsid)
> + continue;
> + if (!list_empty(&h->list) && nvme_tryget_ns_head(h))
> return h;
> }
>
> @@ -3835,7 +3837,11 @@ static void nvme_ns_remove(struct nvme_ns *ns)
>
> mutex_lock(&ns->ctrl->subsys->lock);
> list_del_rcu(&ns->siblings);
> - mutex_unlock(&ns->ctrl->subsys->lock);
> + if (list_empty(&ns->head->list)) {
> + list_del_init(&ns->head->entry);
> + last_path = true;
> + }
> + mutex_unlock(&ns->head->subsys->lock);
>
> /* guarantee not available in head->list */
> synchronize_rcu();
> @@ -3855,13 +3861,6 @@ static void nvme_ns_remove(struct nvme_ns *ns)
> list_del_init(&ns->list);
> up_write(&ns->ctrl->namespaces_rwsem);
>
> - /* Synchronize with nvme_init_ns_head() */
> - mutex_lock(&ns->head->subsys->lock);
> - if (list_empty(&ns->head->list)) {
> - list_del_init(&ns->head->entry);
> - last_path = true;
> - }
> - mutex_unlock(&ns->head->subsys->lock);
> if (last_path)
> nvme_mpath_shutdown_disk(ns->head);
> nvme_put_ns(ns);
>
> _______________________________________________
> Linux-nvme mailing list
> Linux-nvme@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-nvme
>
_______________________________________________
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prev parent reply other threads:[~2021-09-01 14:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-30 9:36 [PATCH v1] nvme: avoid race in shutdown namespace removal Daniel Wagner
2021-08-30 10:04 ` Daniel Wagner
2021-08-30 17:14 ` Hannes Reinecke
2021-09-01 13:30 ` Christoph Hellwig
2021-09-01 14:41 ` Sagi Grimberg [this message]
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