linux-kernel - Re: [PATCH v3] mm/alloc_tag: Fix the kmemleak false positive issue in the allocation of the percpu variable tag->counters

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Message-ID: <aFU7f5fcD9RJ3Mpa@arm.com>
Date: Fri, 20 Jun 2025 11:44:15 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Hao Ge <hao.ge@...ux.dev>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hao Ge <gehao@...inos.cn>
Subject: Re: [PATCH v3] mm/alloc_tag: Fix the kmemleak false positive issue
 in the allocation of the percpu variable tag->counters

On Fri, Jun 20, 2025 at 05:31:02PM +0800, Hao Ge wrote:
> From: Hao Ge <gehao@...inos.cn>
> 
> 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.
> 
> Fixes: 12ca42c23775 ("alloc_tag: allocate percpu counters for module tags dynamically")
> Signed-off-by: Hao Ge <gehao@...inos.cn>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>