Re: [PATCH v2 1/2] PCI/IOV: Revert "PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes"

From: pierre . cregut
Date: Tue Feb 13 2024 - 04:46:35 EST

First sorry for not answering earlier but it is a long time ago. I do
not work on the topic any more (a monitoring tool Skydive, an open
source project no more actively developed as far as I know) and only
have vague memories of it.

kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);
iov->num_VFs = nr_virtfn;

which is identical to how the code looks today. Is it possible that
userspace could react to this uevent and read the stale num_VFs before
iov->num_VFs gets written here? I mean, theoretically it's possible, but
from the bug report it seems like the scenario Pierre was facing was
100% reproducible.
From my memories yes that was exactly the problem. Any stable method
that could detect the change of configuration in user land and ensure
that we get a reliable value of num_vfs after we received it would be

Best regards,

Pierre Crégut

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