From: Dan Williams <dan.j.williams@intel.com>
To: Logan Gunthorpe <logang@deltatee.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Bjorn Helgaas <bhelgaas@google.com>,
Christoph Hellwig <hch@lst.de>, Linux MM <linux-mm@kvack.org>,
linux-pci@vger.kernel.org,
linux-nvdimm <linux-nvdimm@lists.01.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/6] pci/p2pdma: Track pgmap references per resource, not globally
Date: Fri, 29 Mar 2019 12:32:44 -0700 [thread overview]
Message-ID: <CAPcyv4jZiK+OHjwNqDARv4g326AQZx7N_Lmxj1Zux_bX1T2CLQ@mail.gmail.com> (raw)
In-Reply-To: <cfda881b-d99c-7c53-64cb-745ff4b257b0@deltatee.com>
On Fri, Mar 29, 2019 at 10:50 AM Logan Gunthorpe <logang@deltatee.com> wrote:
>
> Thanks Dan, this is great. I think the changes in this series are
> cleaner and more understandable than the patch set I had sent earlier.
>
> However, I found a couple minor issues with this patch:
>
> On 2019-03-29 9:27 a.m., Dan Williams wrote:
> > static void pci_p2pdma_release(void *data)
> > {
> > struct pci_dev *pdev = data;
> > @@ -103,12 +110,12 @@ static void pci_p2pdma_release(void *data)
> > if (!pdev->p2pdma)
> > return;
> >
> > - wait_for_completion(&pdev->p2pdma->devmap_ref_done);
> > - percpu_ref_exit(&pdev->p2pdma->devmap_ref);
> > + /* Flush and disable pci_alloc_p2p_mem() */
> > + pdev->p2pdma = NULL;
> > + synchronize_rcu();
> >
> > gen_pool_destroy(pdev->p2pdma->pool);
>
> I missed this on my initial review, but it became obvious when I tried
> to test the series: this is a NULL dereference seeing pdev->p2pdma was
> set to NULL a few lines up.
Ah, yup.
> When I fix this by storing p2pdma in a local variable, the patch set
> works and never seems to crash when I hot remove p2pdma memory.
Great!
>
> > void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
> > {
> > - void *ret;
> > + void *ret = NULL;
> > + struct percpu_ref *ref;
> >
> > + rcu_read_lock();
> > if (unlikely(!pdev->p2pdma))
> > - return NULL;
>
> Using RCU here makes sense to me, however I expect we should be using
> the proper rcu_assign_pointer(), rcu_dereference() and __rcu tag with
> pdev->p2pdma. If only to better document what's being protected with the
> new RCU calls.
I think just add a comment because those helpers are for cases where
the rcu protected pointer is allowed to race the teardown. In this
case we're using rcu just as a barrier to force the NULL check to
resolve.
next prev parent reply other threads:[~2019-03-29 19:32 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-29 15:27 [PATCH 0/6] mm/devm_memremap_pages: Fix page release race Dan Williams
2019-03-29 15:27 ` [PATCH 1/6] drivers/base/devres: Introduce devm_release_action() Dan Williams
2019-03-29 15:27 ` [PATCH 2/6] mm/devm_memremap_pages: Introduce devm_memunmap_pages Dan Williams
2019-03-29 15:27 ` [PATCH 3/6] pci/p2pdma: Fix the gen_pool_add_virt() failure path Dan Williams
2019-03-29 17:24 ` Bjorn Helgaas
2019-03-29 15:27 ` [PATCH 4/6] lib/genalloc: Introduce chunk owners Dan Williams
2019-03-29 15:27 ` [PATCH 5/6] pci/p2pdma: Track pgmap references per resource, not globally Dan Williams
2019-03-29 17:50 ` Logan Gunthorpe
2019-03-29 19:32 ` Dan Williams [this message]
2019-03-29 15:27 ` [PATCH 6/6] mm/devm_memremap_pages: Fix final page put race Dan Williams
2019-03-29 9:46 ` Ira Weiny
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=CAPcyv4jZiK+OHjwNqDARv4g326AQZx7N_Lmxj1Zux_bX1T2CLQ@mail.gmail.com \
--to=dan.j.williams@intel.com \
--cc=akpm@linux-foundation.org \
--cc=bhelgaas@google.com \
--cc=hch@lst.de \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-nvdimm@lists.01.org \
--cc=linux-pci@vger.kernel.org \
--cc=logang@deltatee.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).