mm, slab: fix use of SLAB_SUPPORTS_SYSFS in kmem_cache_release()

The fix implemented in commit 4ec10268 ("mm, slab: unlink slabinfo,
sysfs and debugfs immediately") caused a subtle side effect due to which
while destroying the kmem cache, the code path would never get into
sysfs_slab_release() function even though SLAB_SUPPORTS_SYSFS is defined
and slab state is FULL. Due to this side effect, we would never release
kobject defined for kmem cache and leak the associated memory.

The issue here's with the use of __is_defined() macro in kmem_cache_
release(). The __is_defined() macro expands to __take_second_arg(
arg1_or_junk 1, 0). If "arg1_or_junk" is defined to 1 then it expands to
__take_second_arg(0, 1, 0) and returns 1. If "arg1_or_junk" is NOT defined
to any value then it expands to __take_second_arg(... 1, 0) and returns 0.

In this particular issue, SLAB_SUPPORTS_SYSFS is defined without any
associated value and that causes __is_defined(SLAB_SUPPORTS_SYSFS) to
always evaluate to 0 and hence it would never invoke sysfs_slab_release().

This patch helps fix this issue by defining SLAB_SUPPORTS_SYSFS to 1.

Fixes: 4ec10268 ("mm, slab: unlink slabinfo, sysfs and debugfs immediately")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/all/CAHj4cs9YCCcfmdxN43-9H3HnTYQsRtTYw1Kzq-L468GfLKAENA@mail.gmail.com/Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

mm/slab.h

@@ -310,7 +310,7 @@ struct kmem_cache {
 };
 
 #if defined(CONFIG_SYSFS) && !defined(CONFIG_SLUB_TINY)
-#define SLAB_SUPPORTS_SYSFS
+#define SLAB_SUPPORTS_SYSFS 1
 void sysfs_slab_unlink(struct kmem_cache *s);
 void sysfs_slab_release(struct kmem_cache *s);
 #else