Re: [PATCH] x86/sgx: Fix free page accounting

[Reinette Chatre]

Hi Jarkko,

On 11/8/2021 12:12 PM, Jarkko Sakkinen wrote:
> On Mon, Nov 08, 2021 at 11:48:18AM -0800, Reinette Chatre wrote:
> > Hi Jarkko,
> >
> > On 11/7/2021 8:47 AM, Jarkko Sakkinen wrote:
> > > On Sun, 2021-11-07 at 18:45 +0200, Jarkko Sakkinen wrote:
> > > > On Thu, 2021-11-04 at 11:28 -0700, Reinette Chatre wrote:
> > > > > The consequence of sgx_nr_free_pages not being protected is that
> > > > > its value may not accurately reflect the actual number of free
> > > > > pages on the system, impacting the availability of free pages in
> > > > > support of many flows. The problematic scenario is when the
> > > > > reclaimer never runs because it believes there to be sufficient
> > > > > free pages while any attempt to allocate a page fails because there
> > > > > are no free pages available. The worst scenario observed was a
> > > > > user space hang because of repeated page faults caused by
> > > > > no free pages ever made available.
> > > >
> > > > Can you go in detail with the "concrete scenario" in the commit
> > > > message? It does not have to describe all the possible scenarios
> > > > but at least one sequence of events.
> >
> >
> > I provided significant detail regarding the "concrete scenario" in a
> > separate response to Greg:
> > https://lore.kernel.org/lkml/a636290d-db04-be16-1c86-a8dcc3719b39@xxxxxxxxx/
> >
> > That message details the test that was run (the test hangs before the fix
> > and can complete after the fix), the traces captured at the time the test
> > hung, analysis of the traces with root cause of why the system is hung,
> > traces after fix applied demonstrating why user space is able to make
> > progress and explaining why the test can complete.
>
> For me that sequence looks like something that you could "abstract"
> a bit and get a rough description of the concurrency scenario.
>
> It is as important in this type of patch, as the code change itself,
> not least because it helps with maintaining in the future to have
> that info in some level of detail in the commit log.

My apologies. I understood your comment to be a concern with the change 
itself instead of just the commit message. I will add more detail about 
the failing scenario encountered to the commit message.

Reinette