mm/alloc_tag: fix the kmemleak false positive issue in the allocation of the percpu variable tag->counters

When loading a module, as long as the module has memory allocation
operations, kmemleak produces a false positive report that resembles the
following:

unreferenced object (percpu) 0x7dfd232a1650 (size 16):
comm "modprobe", pid 1301, jiffies 4294940249
hex dump (first 16 bytes on cpu 2):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc 0):
kmemleak_alloc_percpu+0xb4/0xd0
pcpu_alloc_noprof+0x700/0x1098
load_module+0xd4/0x348
codetag_module_init+0x20c/0x450
codetag_load_module+0x70/0xb8
load_module+0xef8/0x1608
init_module_from_file+0xec/0x158
idempotent_init_module+0x354/0x608
__arm64_sys_finit_module+0xbc/0x150
invoke_syscall+0xd4/0x258
el0_svc_common.constprop.0+0xb4/0x240
do_el0_svc+0x48/0x68
el0_svc+0x40/0xf8
el0t_64_sync_handler+0x10c/0x138
el0t_64_sync+0x1ac/0x1b0

This is because the module can only indirectly reference
alloc_tag_counters through the alloc_tag section, which misleads kmemleak.

However, we don't have a kmemleak ignore interface for percpu allocations
yet. So let's create one and invoke it for tag->counters.

[[e-mail]: fix build error when CONFIG_DEBUG_KMEMLEAK=n, s/igonore/ignore/]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 12ca42c23775 ("alloc_tag: allocate percpu counters for module tags dynamically")
Signed-off-by: Hao Ge <[e-mail]>
Reviewed-by: Catalin Marinas <[e-mail]>
Acked-by: Suren Baghdasaryan <[e-mail]> [lib/alloc_tag.c]
Cc: Kent Overstreet <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/kmemleak.h

···
 extern void kmemleak_not_leak(const void *ptr) __ref;
 extern void kmemleak_transient_leak(const void *ptr) __ref;
 extern void kmemleak_ignore(const void *ptr) __ref;
+extern void kmemleak_ignore_percpu(const void __percpu *ptr) __ref;
 extern void kmemleak_scan_area(const void *ptr, size_t size, gfp_t gfp) __ref;
 extern void kmemleak_no_scan(const void *ptr) __ref;
 extern void kmemleak_alloc_phys(phys_addr_t phys, size_t size,
···
 {
 }
 static inline void kmemleak_transient_leak(const void *ptr)
+{
+}
+static inline void kmemleak_ignore_percpu(const void __percpu *ptr)
 {
 }
 static inline void kmemleak_ignore(const void *ptr)

lib/alloc_tag.c

···
 #include <linux/seq_buf.h>
 #include <linux/seq_file.h>
 #include <linux/vmalloc.h>
+#include <linux/kmemleak.h>
 
 #define ALLOCINFO_FILE_NAME		"allocinfo"
 #define MODULE_ALLOC_TAG_VMAP_SIZE	(100000UL * sizeof(struct alloc_tag))
···
 			       mod->name);
 			return -ENOMEM;
 		}
-	}
 
+		/*
+		 * Avoid a kmemleak false positive. The pointer to the counters is stored
+		 * in the alloc_tag section of the module and cannot be directly accessed.
+		 */
+		kmemleak_ignore_percpu(tag->counters);
+	}
 	return 0;
 }
 

mm/kmemleak.c

···
 EXPORT_SYMBOL(kmemleak_transient_leak);
 
 /**
+ * kmemleak_ignore_percpu - similar to kmemleak_ignore but taking a percpu
+ *			    address argument
+ * @ptr:	percpu address of the object
+ */
+void __ref kmemleak_ignore_percpu(const void __percpu *ptr)
+{
+	pr_debug("%s(0x%px)\n", __func__, ptr);
+
+	if (kmemleak_enabled && ptr && !IS_ERR_PCPU(ptr))
+		make_black_object((unsigned long)ptr, OBJECT_PERCPU);
+}
+EXPORT_SYMBOL_GPL(kmemleak_ignore_percpu);
+
+/**
  * kmemleak_ignore - ignore an allocated object
  * @ptr:	pointer to beginning of the object
  *