From: Joerg Roedel <joro@8bytes.org>
To: "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@intel.com>
Cc: "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>
Subject: Re: [PATCH] iommu: Remove functions that support private domain
Date: Fri, 15 May 2020 11:59:19 +0200 [thread overview]
Message-ID: <20200515095919.GQ18353@8bytes.org> (raw)
In-Reply-To: <FFF73D592F13FD46B8700F0A279B802F573A6672@ORSMSX114.amr.corp.intel.com>
On Thu, May 14, 2020 at 11:12:52PM +0000, Prakhya, Sai Praneeth wrote:
> +static int is_driver_bound(struct device *dev, void *not_used)
> +{
> + int ret = 0;
> +
> + device_lock(dev);
> + if (device_is_bound(dev))
> + ret = 1;
> + device_unlock(dev);
> + return ret;
> +}
This locks only one device, so without lock-conversion there could be a
driver probe after the device_unlock(), while we are probing the other
devices of the group.
> [SNIP]
>
> + /*
> + * Check if any device in the group still has a driver binded to it.
> + * This might race with device driver probing code and unfortunately
> + * there is no clean way out of that either, locking all devices in the
> + * group and then do the re-attach will introduce a lock-inversion with
> + * group->mutex - Joerg.
> + */
> + if (iommu_group_for_each_dev(group, NULL, is_driver_bound)) {
> + pr_err("Active drivers exist for devices in the group\n");
> + return -EBUSY;
> + }
The lock inversion comes into the picture when this code is called from
device(-driver) core through the bus-notifiers. The notifiers are called
with the device already locked.
> Another question I have is.. if it's racy then it should be racy even
> for one device iommu groups.. right? Why would it be racy only with
> multiple devices iommu group?
Valid point. So the device needs to be locked _while_ the default domain
change happens. If triggered by sysfs there should be no locking
problems, I guess. But you better try it out.
Regards,
Joerg
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next prev parent reply other threads:[~2020-05-15 9:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 22:47 [PATCH] iommu: Remove functions that support private domain Sai Praneeth Prakhya
2020-05-14 13:13 ` Joerg Roedel
2020-05-14 17:51 ` Prakhya, Sai Praneeth
2020-05-14 18:32 ` Joerg Roedel
2020-05-14 18:44 ` Prakhya, Sai Praneeth
2020-05-14 19:56 ` Joerg Roedel
2020-05-14 23:12 ` Prakhya, Sai Praneeth
2020-05-15 9:59 ` Joerg Roedel [this message]
2020-05-15 12:55 ` Lu Baolu
2020-05-15 15:46 ` Joerg Roedel
2020-05-17 8:29 ` Prakhya, Sai Praneeth
2020-05-25 13:56 ` Joerg Roedel
2020-05-28 19:31 ` Prakhya, Sai Praneeth
2020-05-15 18:35 ` Prakhya, Sai Praneeth
2020-05-15 10:01 ` Joerg Roedel
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