linux-kernel - Re: [PATCH 3/3] msi: free msi_desc entry only after we've released the kobject

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Date:	Wed, 25 Sep 2013 15:34:58 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Veaceslav Falico <vfalico@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 3/3] msi: free msi_desc entry only after we've released
 the kobject

On Mon, Sep 16, 2013 at 7:47 PM, Veaceslav Falico <vfalico@...hat.com> wrote:
> Currently, we first do kobject_put(&entry->kobj) and the kfree(entry),
> however kobject_put() doesn't guarantee us that it was the last reference
> and that the kobj isn't used currently by someone else, so after we
> kfree(entry) with the struct kobject - other users will begin using the
> freed memory, instead of the actual kobject.
>
> Fix this by using the kobject->release callback, which is called last when
> the kobject is indeed not used and is cleaned up - it's msi_kobj_release(),
> which can do the kfree(entry) safely (kobject_put/cleanup doesn't use the
> kobj itself after ->release() was called, so we're safe).
>
> In case we've failed to create the sysfs directories - just kfree()
> it - cause we don't have the kobjects attached.
>
> Also, remove the same functionality from populate_msi_sysfs(), cause on
> failure we anyway call free_msi_irqs(), which will take care of all the
> kobjects properly.

I agree; it looks like populate_msi_sysfs() doesn't need to have the
cleanup in it.  Can you split that into a separate patch, since I
don't think it depends on the kfree() fix?

Bjorn

> CC: Bjorn Helgaas <bhelgaas@...gle.com>
> CC: linux-pci@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> Signed-off-by: Veaceslav Falico <vfalico@...hat.com>
> ---
>  drivers/pci/msi.c | 27 +++++++++------------------
>  1 file changed, 9 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index 68da921..c9236e4 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -374,19 +374,22 @@ static void free_msi_irqs(struct pci_dev *dev)
>                                 iounmap(entry->mask_base);
>                 }
>
> +               list_del(&entry->list);
> +
>                 /*
>                  * Its possible that we get into this path
>                  * When populate_msi_sysfs fails, which means the entries
>                  * were not registered with sysfs.  In that case don't
> -                * unregister them.
> +                * unregister them, and just free. Otherwise the
> +                * kobject->release will take care of freeing the entry via
> +                * msi_kobj_release().
>                  */
>                 if (entry->kobj.parent) {
>                         kobject_del(&entry->kobj);
>                         kobject_put(&entry->kobj);
> +               } else {
> +                       kfree(entry);
>                 }
> -
> -               list_del(&entry->list);
> -               kfree(entry);
>         }
>
>         kset_unregister(dev->msi_kset);
> @@ -512,6 +515,7 @@ static void msi_kobj_release(struct kobject *kobj)
>         struct msi_desc *entry = to_msi_desc(kobj);
>
>         pci_dev_put(entry->dev);
> +       kfree(entry);
>  }
>
>  static struct kobj_type msi_irq_ktype = {
> @@ -525,7 +529,6 @@ static int populate_msi_sysfs(struct pci_dev *pdev)
>         struct msi_desc *entry;
>         struct kobject *kobj;
>         int ret;
> -       int count = 0;
>
>         pdev->msi_kset = kset_create_and_add("msi_irqs", NULL, &pdev->dev.kobj);
>         if (!pdev->msi_kset)
> @@ -539,23 +542,11 @@ static int populate_msi_sysfs(struct pci_dev *pdev)
>                                      "%u", entry->irq);
>                 if (ret) {
>                         pci_dev_put(pdev);
> -                       goto out_unroll;
> +                       return ret;
>                 }
> -
> -               count++;
>         }
>
>         return 0;
> -
> -out_unroll:
> -       list_for_each_entry(entry, &pdev->msi_list, list) {
> -               if (!count)
> -                       break;
> -               kobject_del(&entry->kobj);
> -               kobject_put(&entry->kobj);
> -               count--;
> -       }
> -       return ret;
>  }
>
>  /**
> --
> 1.8.4
>
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