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

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Uros Bizjak <[email protected]>
Cc: Phillip Lougher <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ubizjak

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);