linux-kernel - Re: [PATCH 12/16] mm: update resctl to use mmap_prepare, mmap_complete, mmap

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Message-ID: <d8ccda47-aad1-4900-be48-ae413d55d98f@lucifer.local>
Date: Mon, 8 Sep 2025 15:27:55 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH 12/16] mm: update resctl to use mmap_prepare,
 mmap_complete, mmap_abort

On Mon, Sep 08, 2025 at 10:24:47AM -0300, Jason Gunthorpe wrote:
> On Mon, Sep 08, 2025 at 12:10:43PM +0100, Lorenzo Stoakes wrote:
> > resctl uses remap_pfn_range(), but holds a mutex over the
> > operation. Therefore, establish the mutex in mmap_prepare(), release it in
> > mmap_complete() and release it in mmap_abort() should the operation fail.
>
> The mutex can't do anything relative to remap_pfn, no reason to hold it.

Sorry I missed this bit before...

Yeah I guess my concern was that the original code very intentionally holds the
mutex _over the remap operation_.

But I guess given we release the lock on failure this isn't necessary, and of
course obviously the lock has no bearing ont he actual remap.

Will drop it and drop mmap_abort for now as it's not yet needed.

Cheers, Lorenzo