[regression] tracing: kmemleak warning in allocate_cmdlines_buffer()

From: Kalle Valo <kvalo@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: regressions@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org,
	Jeff Johnson <quic_jjohnson@quicinc.com>
Subject: [regression] tracing: kmemleak warning in allocate_cmdlines_buffer()
Date: Wed, 14 Feb 2024 14:50:56 +0200	[thread overview]
Message-ID: <87r0hfnr9r.fsf@kernel.org> (raw)

Hi Steven,

I upgraded our ath11k test setup to v6.8-rc4 and noticed a new kmemleak
warning in the log:

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

I don't see this warning in v6.8-rc3 and also reverting commit
44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
makes the warning go away. Let me know if you need more info or help
with testing, I see the warning every time so it's easy to reproduce.

Kalle