From: Nicolin Chen <nicolinc@nvidia.com>
To: "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Krishna Reddy <vdumpa@nvidia.com>, Will Deacon <will@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Joerg Roedel <joro@8bytes.org>,
Jonathan Hunter <jonathanh@nvidia.com>,
<linux-kernel@vger.kernel.org>, <iommu@lists.linux.dev>,
<linux-arm-kernel@lists.infradead.org>,
<linux-tegra@vger.kernel.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
<linux-rt-devel@lists.linux.dev>
Subject: Re: [PATCH v2] iommu/tegra241-cmdqv: do not use smp_processor_id in preemptible context
Date: Mon, 9 Dec 2024 11:03:01 -0800 [thread overview]
Message-ID: <Z1c+5dI7fibEZZ/h@Asurada-Nvidia> (raw)
In-Reply-To: <Z1L1mja3nXzsJ0Pk@uudg.org>
On Fri, Dec 06, 2024 at 10:01:14AM -0300, Luis Claudio R. Goncalves wrote:
> During boot some of the calls to tegra241_cmdqv_get_cmdq() will happen
> in preemptible context. As this function calls smp_processor_id(), if
> CONFIG_DEBUG_PREEMPT is enabled, these calls will trigger a series of
> "BUG: using smp_processor_id() in preemptible" backtraces.
Confirmed the BUG prints. Should we CC stable tree?
> As tegra241_cmdqv_get_cmdq() only calls smp_processor_id() to use the
> CPU number as a factor to balance out traffic on cmdq usage, it is safe
> to use raw_smp_processor_id() here.
>
> v2: Sebastian helped identify that the problem was not exclusive to kernels
> with PREEMPT_RT enabled. The delta between v1 and v2 is the description.
>
> Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Thanks
Nicolin
next prev parent reply other threads:[~2024-12-09 19:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-06 13:01 [PATCH v2] iommu/tegra241-cmdqv: do not use smp_processor_id in preemptible context Luis Claudio R. Goncalves
2024-12-09 14:20 ` Jason Gunthorpe
2024-12-09 19:03 ` Nicolin Chen [this message]
2024-12-10 0:17 ` Will Deacon
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