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 <[email protected]>
---
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/[email protected]/
[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
On 2024-01-04 12:52, 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 <[email protected]>
This makes sense to me. Though, the use of RCU could probably use a
review. Seeing p2pdma is only released through a devm action on the
pdev, I would think it shouldn't be needed if we hold a reference to the
pdev.
Other than that:
Reviewed-by: Logan Gunthorpe <[email protected]>
Thanks!
Logan
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 <[email protected]>
> ---
> 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/[email protected]/
> [2]: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/RCU/whatisRCU.rst#n161
Looks good to me.
Smatch is supposed to catch this sort of bug but there are some issues
with xa_store it's normally holding the the xas_lock() but if you pass
a sleeping GFP_ then it drops the lock in __xas_nomem(). Sort of
tricky. So right now all xa_store() stuff triggers a false positive
but tomorrows version of Smatch will just miss this bug.
regards,
dan carpenter
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 <[email protected]>
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/[email protected]/
> [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
>