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From: Kalle Valo <kvalo@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,  Linux Trace Kernel
 <linux-trace-kernel@vger.kernel.org>,  Masami Hiramatsu
 <mhiramat@kernel.org>,  Mathieu Desnoyers
 <mathieu.desnoyers@efficios.com>,  Catalin Marinas
 <catalin.marinas@arm.com>
Subject: Re: [PATCH v2] tracing: Inform kmemleak of saved_cmdlines allocation
References: <20240214112046.09a322d6@gandalf.local.home>
Date: Wed, 14 Feb 2024 20:20:22 +0200
In-Reply-To: <20240214112046.09a322d6@gandalf.local.home> (Steven Rostedt's
	message of "Wed, 14 Feb 2024 11:20:46 -0500")
Message-ID: <87h6iaewm1.fsf@kernel.org>
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Steven Rostedt <rostedt@goodmis.org> writes:

> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
>
> The allocation of the struct saved_cmdlines_buffer structure changed from:
>
>         s = kmalloc(sizeof(*s), GFP_KERNEL);
> 	s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);
>
> to:
>
> 	orig_size = sizeof(*s) + val * TASK_COMM_LEN;
> 	order = get_order(orig_size);
> 	size = 1 << (order + PAGE_SHIFT);
> 	page = alloc_pages(GFP_KERNEL, order);
> 	if (!page)
> 		return NULL;
>
> 	s = page_address(page);
> 	memset(s, 0, sizeof(*s));
>
> 	s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);
>
> Where that s->saved_cmdlines allocation looks to be a dangling allocation
> to kmemleak. That's because kmemleak only keeps track of kmalloc()
> allocations. For allocations that use page_alloc() directly, the kmemleak
> needs to be explicitly informed about it.
>
> Add kmemleak_alloc() and kmemleak_free() around the page allocation so
> that it doesn't give the following false positive:
>
> unreferenced object 0xffff8881010c8000 (size 32760):
>   comm "swapper", pid 0, jiffies 4294667296
>   hex dump (first 32 bytes):
>     ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
>     ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
>   backtrace (crc ae6ec1b9):
>     [<ffffffff86722405>] kmemleak_alloc+0x45/0x80
>     [<ffffffff8414028d>] __kmalloc_large_node+0x10d/0x190
>     [<ffffffff84146ab1>] __kmalloc+0x3b1/0x4c0
>     [<ffffffff83ed7103>] allocate_cmdlines_buffer+0x113/0x230
>     [<ffffffff88649c34>] tracer_alloc_buffers.isra.0+0x124/0x460
>     [<ffffffff8864a174>] early_trace_init+0x14/0xa0
>     [<ffffffff885dd5ae>] start_kernel+0x12e/0x3c0
>     [<ffffffff885f5758>] x86_64_start_reservations+0x18/0x30
>     [<ffffffff885f582b>] x86_64_start_kernel+0x7b/0x80
>     [<ffffffff83a001c3>] secondary_startup_64_no_verify+0x15e/0x16b
>
> Link: https://lore.kernel.org/linux-trace-kernel/87r0hfnr9r.fsf@kernel.org/
>
> Fixes: 44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
> Reported-by: Kalle Valo <kvalo@kernel.org>
> Tested-by: Kalle Valo <kvalo@kernel.org>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Applies cleanly to v6.8-rc4 and I don't see the leak anymore, thank you
for fixing it so quickly!

Tested-by: Kalle Valo <kvalo@kernel.org>

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