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

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Date: Thu,  4 Jan 2024 20:52:35 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Eric Dumazet <edumazet@...gle.com>
Cc: alexis.lothore@...tlin.com,
	linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	linux-pci@...r.kernel.org
Subject: [PATCH] PCI/P2PDMA: Fix a sleeping issue in a RCU read section

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>
---
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