From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AA3521B273 for ; Mon, 18 Dec 2023 11:05:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="e/6tJhhM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C1E73C433C7; Mon, 18 Dec 2023 11:05:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1702897552; bh=tLlIfC2a3neFEzwxH223OeKz1xxLNHJaqaYBYGCmJp0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=e/6tJhhM5qoLbgiTOZeugGEzpRmZRLTiEUaBRHZORpY+P5lQiqUKwfxYhhaRfi91H IwD5XxHQ9+0BKso6+mVPKSIz21jp74YxuBPmTRp+P4JTOGB8U+kxev3i3KTyN9Kk7T 5pOV3deZeFDf5dVm3WhbBKiDMnZDonH1CG1FaQd0= Date: Mon, 18 Dec 2023 12:05:49 +0100 From: Greg KH To: Naveen N Rao Cc: stable@vger.kernel.org, Michael Ellerman Subject: Re: [PATCH 5.15.y 1/2] powerpc/ftrace: Create a dummy stackframe to fix stack unwind Message-ID: <2023121842-vertebrae-sedative-4e9e@gregkh> References: <2023080733-wife-elope-de1b@gregkh> <20231215111433.2362641-1-naveen@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231215111433.2362641-1-naveen@kernel.org> On Fri, Dec 15, 2023 at 04:44:32PM +0530, Naveen N Rao wrote: > commit 41a506ef71eb38d94fe133f565c87c3e06ccc072 upstream. > > With ppc64 -mprofile-kernel and ppc32 -pg, profiling instructions to > call into ftrace are emitted right at function entry. The instruction > sequence used is minimal to reduce overhead. Crucially, a stackframe is > not created for the function being traced. This breaks stack unwinding > since the function being traced does not have a stackframe for itself. > As such, it never shows up in the backtrace: > > /sys/kernel/debug/tracing # echo 1 > /proc/sys/kernel/stack_tracer_enabled > /sys/kernel/debug/tracing # cat stack_trace > Depth Size Location (17 entries) > ----- ---- -------- > 0) 4144 32 ftrace_call+0x4/0x44 > 1) 4112 432 get_page_from_freelist+0x26c/0x1ad0 > 2) 3680 496 __alloc_pages+0x290/0x1280 > 3) 3184 336 __folio_alloc+0x34/0x90 > 4) 2848 176 vma_alloc_folio+0xd8/0x540 > 5) 2672 272 __handle_mm_fault+0x700/0x1cc0 > 6) 2400 208 handle_mm_fault+0xf0/0x3f0 > 7) 2192 80 ___do_page_fault+0x3e4/0xbe0 > 8) 2112 160 do_page_fault+0x30/0xc0 > 9) 1952 256 data_access_common_virt+0x210/0x220 > 10) 1696 400 0xc00000000f16b100 > 11) 1296 384 load_elf_binary+0x804/0x1b80 > 12) 912 208 bprm_execve+0x2d8/0x7e0 > 13) 704 64 do_execveat_common+0x1d0/0x2f0 > 14) 640 160 sys_execve+0x54/0x70 > 15) 480 64 system_call_exception+0x138/0x350 > 16) 416 416 system_call_common+0x160/0x2c4 > > Fix this by having ftrace create a dummy stackframe for the function > being traced. With this, backtraces now capture the function being > traced: > > /sys/kernel/debug/tracing # cat stack_trace > Depth Size Location (17 entries) > ----- ---- -------- > 0) 3888 32 _raw_spin_trylock+0x8/0x70 > 1) 3856 576 get_page_from_freelist+0x26c/0x1ad0 > 2) 3280 64 __alloc_pages+0x290/0x1280 > 3) 3216 336 __folio_alloc+0x34/0x90 > 4) 2880 176 vma_alloc_folio+0xd8/0x540 > 5) 2704 416 __handle_mm_fault+0x700/0x1cc0 > 6) 2288 96 handle_mm_fault+0xf0/0x3f0 > 7) 2192 48 ___do_page_fault+0x3e4/0xbe0 > 8) 2144 192 do_page_fault+0x30/0xc0 > 9) 1952 608 data_access_common_virt+0x210/0x220 > 10) 1344 16 0xc0000000334bbb50 > 11) 1328 416 load_elf_binary+0x804/0x1b80 > 12) 912 64 bprm_execve+0x2d8/0x7e0 > 13) 848 176 do_execveat_common+0x1d0/0x2f0 > 14) 672 192 sys_execve+0x54/0x70 > 15) 480 64 system_call_exception+0x138/0x350 > 16) 416 416 system_call_common+0x160/0x2c4 > > This results in two additional stores in the ftrace entry code, but > produces reliable backtraces. > > Fixes: 153086644fd1 ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI") > Cc: stable@vger.kernel.org > Signed-off-by: Naveen N Rao > Signed-off-by: Michael Ellerman > Link: https://msgid.link/20230621051349.759567-1-naveen@kernel.org > --- > arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > All now queued up, thanks. greg k-h