linux-kernel - [PATCH] devres: Correclty strip percpu address space of devm_free

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Message-ID: <20240830083406.9695-1-ubizjak@gmail.com>
Date: Fri, 30 Aug 2024 10:33:52 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>
Subject: [PATCH] devres: Correclty strip percpu address space of devm_free_percpu() argument

devm_free_percpu() calls devres_release() with a pointer in percpu
address space. devres_release() expects pointers in the generic address
space, so address space needs to be stripped from the argument.

When strict percpu address space checks are enabled, then the current
direct cast from the percpu address space to the generic address space
fails the compilation on x86_64 with:

devres.c:1234:32: error: cast to generic address space pointer from disjoint ‘__seg_gs’ address space pointer

Add intermediate casts to unsigned long to remove address space of
the pointer before casting it to the generic AS, as advised in [1]
and [2].

Side note: sparse still requires __force, although the documentation
[2] allows casts to unsigned long without __force attribute.

Found by GCC's named address space checks.

There were no changes in the resulting object file.

[1] https://gcc.gnu.org/onlinedocs/gcc/Named-Address-Spaces.html#x86-Named-Address-Spaces
[2] https://sparse.docs.kernel.org/en/latest/annotations.html#address-space-name

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
---
 drivers/base/devres.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index a2ce0ead06a6..2152eec0c135 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -1231,6 +1231,6 @@ void devm_free_percpu(struct device *dev, void __percpu *pdata)
 	 * devm_free_pages() does.
 	 */
 	WARN_ON(devres_release(dev, devm_percpu_release, devm_percpu_match,
-			       (__force void *)pdata));
+			       (void *)(__force unsigned long)pdata));
 }
 EXPORT_SYMBOL_GPL(devm_free_percpu);
-- 
2.46.0