linux-kernel - Re: [PATCH] iommu: Avoid introducing more races

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Message-ID: <20250320194258.GK206770@nvidia.com>
Date: Thu, 20 Mar 2025 16:42:58 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Robin Murphy <robin.murphy@....com>
Cc: joro@...tes.org, will@...nel.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: Avoid introducing more races

On Tue, Mar 11, 2025 at 03:19:25PM +0000, Robin Murphy wrote:
> Although the lock-juggling is only a temporary workaround, we don't want
> it to make things avoidably worse. Jason was right to be nervous, since
> bus_iommu_probe() doesn't care *which* IOMMU instance it's probing for,
> so it probably is possible for one walk to finish a probe which a
> different walk started, thus we do want to check for that.
> 
> Also there's no need to drop the lock just to have of_iommu_configure()
> do nothing when a fwspec already exists; check that directly and avoid
> opening a window at all in that (still somewhat likely) case.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> I was rather expecting to send a v3 of "iommu: Get DT/ACPI parsing into
> the proper probe path", so I'm grateful that v2 was picked up, thanks!
> This is the difference as a fix/squash commit instead.
> ---
>  drivers/iommu/iommu.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason