linux-kernel - Re: [PATCH] iommu/amd: move wait_on

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Message-ID: <is5wyo3x5ynjjjhqbpbzdbqcqvht45xrdfmy64osi3a7rzkx4g@bpuj5n32a54p>
Date: Sat, 10 Jan 2026 10:54:57 +0100
From: Jörg Rödel <joro@...tes.org>
To: Ankit Soni <Ankit.Soni@....com>
Cc: iommu@...ts.linux.dev, vasant.hegde@....com, 
	suravee.suthikulpanit@....com, will@...nel.org, robin.murphy@....com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/amd: move wait_on_sem() out of spinlock

On Mon, Dec 01, 2025 at 02:39:40PM +0000, Ankit Soni wrote:
> With iommu.strict=1, the existing completion wait path can cause soft
> lockups under stressed environment, as wait_on_sem() busy-waits under the
> spinlock with interrupts disabled.
> 
> Move the completion wait in iommu_completion_wait() out of the spinlock.
> wait_on_sem() only polls the hardware-updated cmd_sem and does not require
> iommu->lock, so holding the lock during the busy wait unnecessarily
> increases contention and extends the time with interrupts disabled.
> 
> Signed-off-by: Ankit Soni <Ankit.Soni@....com>
> ---
>  drivers/iommu/amd/iommu.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)

Applied, thanks.