From f5769359c5b241978e6933672bb78b3adc36aa18 Mon Sep 17 00:00:00 2001 From: Hao Ge Date: Fri, 20 Jun 2025 02:31:54 +0800 Subject: [PATCH] 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. [gehao@kylinos.cn: fix build error when CONFIG_DEBUG_KMEMLEAK=n, s/igonore/ignore/] Link: https://lkml.kernel.org/r/20250620093102.2416767-1-hao.ge@linux.dev Link: https://lkml.kernel.org/r/20250619183154.2122608-1-hao.ge@linux.dev Fixes: 12ca42c23775 ("alloc_tag: allocate percpu counters for module tags dynamically") Signed-off-by: Hao Ge Reviewed-by: Catalin Marinas Acked-by: Suren Baghdasaryan [lib/alloc_tag.c] Cc: Kent Overstreet Signed-off-by: Andrew Morton --- include/linux/kmemleak.h | 4 ++++ lib/alloc_tag.c | 8 +++++++- mm/kmemleak.c | 14 ++++++++++++++ 3 files changed, 25 insertions(+), 1 deletion(-) diff --git a/include/linux/kmemleak.h b/include/linux/kmemleak.h index 93a73c076d16..fbd424b2abb1 100644 --- a/include/linux/kmemleak.h +++ b/include/linux/kmemleak.h @@ -28,6 +28,7 @@ extern void kmemleak_update_trace(const void *ptr) __ref; 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, @@ -97,6 +98,9 @@ static inline void kmemleak_not_leak(const void *ptr) 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) { } diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index d48b80f3f007..3a74d63a959e 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -10,6 +10,7 @@ #include #include #include +#include #define ALLOCINFO_FILE_NAME "allocinfo" #define MODULE_ALLOC_TAG_VMAP_SIZE (100000UL * sizeof(struct alloc_tag)) @@ -632,8 +633,13 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag 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; } diff --git a/mm/kmemleak.c b/mm/kmemleak.c index da9cee34ee1b..8d588e685311 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1246,6 +1246,20 @@ void __ref kmemleak_transient_leak(const void *ptr) } 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 -- 2.50.1