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

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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: 12ca42c237 ("alloc_tag: allocate percpu counters for module tags dynamically")
Signed-off-by: Hao Ge <gehao@kylinos.cn>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Suren Baghdasaryan <surenb@google.com>	[lib/alloc_tag.c]
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Hao Ge 2025-06-20 02:31:54 +08:00 • committed by Andrew Morton
parent df831e9773
commit f5769359c5
3 changed files with 25 additions and 1 deletions
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4
include/linux/kmemleak.h
View file

@ -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)
{
}

8
lib/alloc_tag.c
View file

@ -10,6 +10,7 @@
#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))
@ -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;
}

14
mm/kmemleak.c
View file

@ -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