linux-kernel - Re: [PATCH] PCI/P2PDMA: Fix a sleeping issue in a RCU read section

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Date: Thu, 8 Feb 2024 15:33:13 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Eric Dumazet <edumazet@...gle.com>, alexis.lothore@...tlin.com,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI/P2PDMA: Fix a sleeping issue in a RCU read section

On Thu, Jan 04, 2024 at 08:52:35PM +0100, Christophe JAILLET wrote:
> It is not allowed to sleep within a RCU read section, so use GFP_ATOMIC
> instead of GFP_KERNEL here.
> 
> Fixes: ae21f835a5bd ("PCI/P2PDMA: Finish RCU conversion of pdev->p2pdma")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>

Applied with Logan's Reviewed-by to pci/p2pdma for v6.9, thanks!

> ---
> This patch is speculative.
> It is based on a discussion related to another patch. See [1].
> 
> It also matches the doc, IIUC. See [2]
> 
> [1]: https://lore.kernel.org/all/20240104143925.194295-3-alexis.lothore@bootlin.com/
> [2]: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/RCU/whatisRCU.rst#n161
> ---
>  drivers/pci/p2pdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 0c361561b855..4f47a13cb500 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -661,7 +661,7 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
>  	p2pdma = rcu_dereference(provider->p2pdma);
>  	if (p2pdma)
>  		xa_store(&p2pdma->map_types, map_types_idx(client),
> -			 xa_mk_value(map_type), GFP_KERNEL);
> +			 xa_mk_value(map_type), GFP_ATOMIC);
>  	rcu_read_unlock();
>  	return map_type;
>  }
> -- 
> 2.34.1
>