From: Alejandro Lucero <alejandro.lucero@netronome.com>
To: "Burakov, Anatoly" <anatoly.burakov@intel.com>
Cc: Thomas Monjalon <thomas@monjalon.net>,
lei.a.yao@intel.com, dev <dev@dpdk.org>,
"Xu, Qian Q" <qian.q.xu@intel.com>,
xueqin.lin@intel.com, Ferruh Yigit <ferruh.yigit@intel.com>
Subject: Re: [dpdk-dev] [PATCH v3 0/6] use IOVAs check based on DMA mask
Date: Tue, 30 Oct 2018 10:19:35 +0000 [thread overview]
Message-ID: <CAD+H991PPF9BXzsek4A8dh5_W6DkTmP670-wQYE25_uxHdcspQ@mail.gmail.com> (raw)
In-Reply-To: <30339c03-6ec2-f72a-d113-5b150f441bf9@intel.com>
On Tue, Oct 30, 2018 at 10:11 AM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:
> On 29-Oct-18 2:18 PM, Thomas Monjalon wrote:
> > 29/10/2018 14:40, Alejandro Lucero:
> >> On Mon, Oct 29, 2018 at 1:18 PM Yao, Lei A <lei.a.yao@intel.com> wrote:
> >>> *From:* Alejandro Lucero [mailto:alejandro.lucero@netronome.com]
> >>> On Mon, Oct 29, 2018 at 11:46 AM Thomas Monjalon <thomas@monjalon.net>
> >>> wrote:
> >>>
> >>> 29/10/2018 12:39, Alejandro Lucero:
> >>>> I got a patch that solves a bug when calling rte_eal_dma_mask using
> the
> >>>> mask instead of the maskbits. However, this does not solves the
> >>> deadlock.
> >>>
> >>> The deadlock is a bigger concern I think.
> >>>
> >>> I think once the call to rte_eal_check_dma_mask uses the maskbits
> instead
> >>> of the mask, calling rte_memseg_walk_thread_unsafe avoids the deadlock.
> >>>
> >>> Yao, can you try with the attached patch?
> >>>
> >>> Hi, Lucero
> >>>
> >>> This patch can fix the issue at my side. Thanks a lot
> >>> for you quick action.
> >>
> >> Great!
> >>
> >> I will send an official patch with the changes.
> >
> > Please, do not forget my other request to better comment functions.
> >
> >
> >> I have to say that I tested the patchset, but I think it was where
> >> legacy_mem was still there and therefore dynamic memory allocation code
> not
> >> used during memory initialization.
> >>
> >> There is something that concerns me though. Using
> >> rte_memseg_walk_thread_unsafe could be a problem under some situations
> >> although those situations being unlikely.
> >>
> >> Usually, calling rte_eal_check_dma_mask happens during initialization.
> Then
> >> it is safe to use the unsafe function for walking memsegs, but with
> device
> >> hotplug and dynamic memory allocation, there exists a potential race
> >> condition when the primary process is allocating more memory and
> >> concurrently a device is hotplugged and a secondary process does the
> device
> >> initialization. By now, this is just a problem with the NFP, and the
> >> potential race condition window really unlikely, but I will work on this
> >> asap.
> >
> > Yes, this is what concerns me.
> > You can add a comment explaining the unsafe which is not handled.
>
> The issue here is that this code is called from both memory-locked and
> memory-unlocked context. Virtio had a similar issue with their mem table
> update code - they solved it by manually locking the memory before doing
> everything else, and using thread_unsafe version of the walk.
>
> Could something like that be done here?
>
>
I have a patch adding a safe and an unsafe dma mask check versions.
However, because the multiprocess problem reported, I think the fixing
requires other type of work.
The problem I see now is calling rte_eal_check_dma_mask from set_iova_mode
code path is wrong. This can not be done at that point because the memory
has not been initialized yet.
> >
> >
> >>>> Interestingly, the problem looks like a compiler one. Calling
> >>>> rte_memseg_walk does not return when calling inside rt_eal_dma_mask,
> >>> but if
> >>>> you modify the call like this:
> >>>>
> >>>> - if (rte_memseg_walk(check_iova, &mask))
> >>>> + if (!rte_memseg_walk(check_iova, &mask))
> >>>>
> >>>> it works, although the value returned to the invoker changes, of
> course.
> >>>> But the point here is it should be the same behaviour when calling
> >>>> rte_memseg_walk than before and it is not.
> >>>
> >>> Anyway, the coding style requires to save the return value in a
> variable,
> >>> instead of nesting the call in an "if" condition.
> >>> And the "if" check should be explicitly != 0 because it is not a real
> >>> boolean.
> >>>
> >>> PS: please do not top post and avoid HTML emails, thanks
> >>>
> >>>
> >>
> >
> >
> >
> >
> >
> >
>
>
> --
> Thanks,
> Anatoly
>
next prev parent reply other threads:[~2018-10-30 10:19 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-05 12:45 Alejandro Lucero
2018-10-05 12:45 ` [dpdk-dev] [PATCH v3 1/6] mem: add function for checking memsegs IOVAs addresses Alejandro Lucero
2018-10-10 8:56 ` Tu, Lijuan
2018-10-11 9:26 ` Alejandro Lucero
2018-10-28 21:03 ` Thomas Monjalon
2018-10-05 12:45 ` [dpdk-dev] [PATCH v3 2/6] mem: use address hint for mapping hugepages Alejandro Lucero
2018-10-29 16:08 ` Dariusz Stojaczyk
2018-10-29 16:40 ` Alejandro Lucero
2018-10-05 12:45 ` [dpdk-dev] [PATCH v3 3/6] bus/pci: check iommu addressing limitation just once Alejandro Lucero
2018-10-05 12:45 ` [dpdk-dev] [PATCH v3 4/6] bus/pci: use IOVAs dmak mask check when setting IOVA mode Alejandro Lucero
2018-10-05 12:45 ` [dpdk-dev] [PATCH v3 5/6] net/nfp: check hugepages IOVAs based on DMA mask Alejandro Lucero
2018-10-05 12:45 ` [dpdk-dev] [PATCH v3 6/6] net/nfp: support IOVA VA mode Alejandro Lucero
2018-10-28 21:04 ` [dpdk-dev] [PATCH v3 0/6] use IOVAs check based on DMA mask Thomas Monjalon
2018-10-29 8:23 ` Yao, Lei A
2018-10-29 8:42 ` Thomas Monjalon
2018-10-29 9:07 ` Thomas Monjalon
2018-10-29 9:25 ` Alejandro Lucero
2018-10-29 9:44 ` Yao, Lei A
2018-10-29 9:36 ` Yao, Lei A
2018-10-29 9:48 ` Thomas Monjalon
2018-10-29 10:11 ` Alejandro Lucero
2018-10-29 10:15 ` Alejandro Lucero
2018-10-29 11:39 ` Alejandro Lucero
2018-10-29 11:46 ` Thomas Monjalon
2018-10-29 12:55 ` Alejandro Lucero
2018-10-29 13:18 ` Yao, Lei A
2018-10-29 13:40 ` Alejandro Lucero
2018-10-29 14:18 ` Thomas Monjalon
2018-10-29 14:35 ` Alejandro Lucero
2018-10-29 18:54 ` Yongseok Koh
2018-10-29 19:37 ` Alejandro Lucero
2018-10-30 10:10 ` Burakov, Anatoly
2018-10-30 10:11 ` Burakov, Anatoly
2018-10-30 10:19 ` Alejandro Lucero [this message]
2018-10-30 3:20 ` Lin, Xueqin
2018-10-30 9:41 ` Alejandro Lucero
2018-10-30 10:33 ` Lin, Xueqin
2018-10-30 10:38 ` Alejandro Lucero
2018-10-30 12:21 ` Lin, Xueqin
2018-10-30 12:37 ` Alejandro Lucero
2018-10-30 14:04 ` Alejandro Lucero
2018-10-30 14:14 ` Burakov, Anatoly
2018-10-30 14:45 ` Alejandro Lucero
2018-10-30 14:45 ` Lin, Xueqin
2018-10-30 14:57 ` Alejandro Lucero
2018-10-30 15:09 ` Lin, Xueqin
2018-10-30 10:18 ` Burakov, Anatoly
2018-10-30 10:23 ` Alejandro Lucero
-- strict thread matches above, loose matches on Subject: below --
2018-07-04 12:53 Alejandro Lucero
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=CAD+H991PPF9BXzsek4A8dh5_W6DkTmP670-wQYE25_uxHdcspQ@mail.gmail.com \
--to=alejandro.lucero@netronome.com \
--cc=anatoly.burakov@intel.com \
--cc=dev@dpdk.org \
--cc=ferruh.yigit@intel.com \
--cc=lei.a.yao@intel.com \
--cc=qian.q.xu@intel.com \
--cc=thomas@monjalon.net \
--cc=xueqin.lin@intel.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).