Re: [dpdk-dev] [PATCH v3 28/29] ethdev: reset all when releasing a port

[Thomas Monjalon <thomas@monjalon.net>]

29/09/2020 17:50, Ferruh Yigit:
> On 9/29/2020 12:58 PM, Wang, Haiyue wrote:
> > From: Thomas Monjalon <thomas@monjalon.net>
> >> 29/09/2020 12:26, Maxime Coquelin:
> >>> On 9/29/20 1:14 AM, Thomas Monjalon wrote:
> >>>> The function rte_eth_dev_release_port() was resetting partially
> >>>> the struct rte_eth_dev. The drivers were completing it
> >>>> with more pointers set to NULL in the close or remove operations.
> >>>>
> >>>> A full memset is done so most of those assignments become useless.
> >> [...]
> >>> With this patch, I get following segfault at init time with Virtio PMD:
> >>>
> >>>          Program received signal SIGSEGV, Segmentation fault.
> >>>          0x0000000000854c9b in rte_eth_dev_callback_register (port_id=32,
> >>>              event=RTE_ETH_EVENT_UNKNOWN, cb_fn=0x4b24de
> >>> <eth_event_callback>,
> >>>              cb_arg=0x0) at ../lib/librte_ethdev/rte_ethdev.c:4042
> >>>          4042
> >>> TAILQ_INSERT_TAIL(&(dev->link_intr_cbs),
> >>
> >> Yes this is because after closing a port, everything is resetted,
> >> including .link_intr_cbs which is set only once in a constructor:
> >> http://git.dpdk.org/dpdk/commit/?id=9ec0b3869d8
> >>
> >> I can change this patch to selectively set pointers to NULL.
> >>
> >> Or if we prefer a big memset 0, we need to rework how RTE_ETH_ALL
> >> is managed to register a callback for any event.
> >> Instead of setting the callback for all ports, we could have
> >> a special catch-call callback list which is called for all events.
> >> This way we could revert initializing .link_intr_cbs in eth_dev_get().
> >>
> >>
> > 
> > Move 'struct rte_eth_dev_cb_list link_intr_cbs' to the end of 'struct rte_eth_dev',
> > and starting from link_intr_cbs, these members will be kept after closed ? :-)
> > 
> > memset(eth_dev, 0, offsetof(struct rte_eth_dev, link_intr_cbs));
> > 
> 
> This is similar version of a previous patch:
> https://patches.dpdk.org/patch/65795/

I forgot this patch :)

> That one is also waiting because I remember it was not safe for hotplug.

I don't think there is a safety issue.
It makes harder to play with dangling pointers, which is good.
Note: the .device pointer was already resetted by
rte_eth_dev_pci_generic_remove(), and generalized in patch 1.

> Instead of a big memset, I am for selectively set pointers to NULL.

I will prepare the patch with selective resets.