linux-kernel - [PATCH] squashfs: Fix percpu address space issues in decompressor_multi

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Message-ID: <20240830091104.13049-1-ubizjak@gmail.com>
Date: Fri, 30 Aug 2024 11:10:50 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Phillip Lougher <phillip@...ashfs.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] squashfs: Fix percpu address space issues in decompressor_multi_percpu.c

When strict percpu address space checks are enabled, then current
direct casts between the percpu address space and the generic address
space fail the compilation on x86_64 with:

decompressor_multi_percpu.c: In function ‘squashfs_decompressor_create’:
decompressor_multi_percpu.c:49:16: error: cast to generic address space pointer from disjoint ‘__seg_gs’ address space pointer

decompressor_multi_percpu.c: In function ‘squashfs_decompressor_destroy’:
decompressor_multi_percpu.c:64:25: error: cast to ‘__seg_gs’ address space pointer from disjoint generic address space pointer

decompressor_multi_percpu.c: In function ‘squashfs_decompress’:
decompressor_multi_percpu.c:82:25: error: cast to ‘__seg_gs’ address space pointer from disjoint generic address space pointer

Add intermediate casts to unsigned long, as advised in [1] and [2].

Side note: sparse still requires __force when casting from the percpu
address space, 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: Phillip Lougher <phillip@...ashfs.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 fs/squashfs/decompressor_multi_percpu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/squashfs/decompressor_multi_percpu.c b/fs/squashfs/decompressor_multi_percpu.c
index 8a218e7c2390..e4d7e507b268 100644
--- a/fs/squashfs/decompressor_multi_percpu.c
+++ b/fs/squashfs/decompressor_multi_percpu.c
@@ -46,7 +46,7 @@ static void *squashfs_decompressor_create(struct squashfs_sb_info *msblk,
 	}
 
 	kfree(comp_opts);
-	return (__force void *) percpu;
+	return (void *)(__force unsigned long) percpu;
 
 out:
 	for_each_possible_cpu(cpu) {
@@ -61,7 +61,7 @@ static void *squashfs_decompressor_create(struct squashfs_sb_info *msblk,
 static void squashfs_decompressor_destroy(struct squashfs_sb_info *msblk)
 {
 	struct squashfs_stream __percpu *percpu =
-			(struct squashfs_stream __percpu *) msblk->stream;
+			(void __percpu *)(unsigned long) msblk->stream;
 	struct squashfs_stream *stream;
 	int cpu;
 
@@ -79,7 +79,7 @@ static int squashfs_decompress(struct squashfs_sb_info *msblk, struct bio *bio,
 {
 	struct squashfs_stream *stream;
 	struct squashfs_stream __percpu *percpu =
-			(struct squashfs_stream __percpu *) msblk->stream;
+			(void __percpu *)(unsigned long) msblk->stream;
 	int res;
 
 	local_lock(&percpu->lock);
-- 
2.46.0