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: <CAJuCfpELs1Y_YaT3-f8-dnsPqkwgGShEVU9tqJe=3RJU3BK_6w@mail.gmail.com>
Date: Sun, 22 Jun 2025 15:40:29 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Hao Ge <hao.ge@...ux.dev>, 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 3:44 AM Catalin Marinas <catalin.marinas@....com> wrote:
>
> 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>

Thanks!
For lib/alloc_tag.c:

Acked-by: Suren Baghdasaryan <surenb@...gle.com>