From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794198996; b=xQu5tztcOGpIFbA3ul7PaVKAypqZavjKu953Mj/o2SbAqXRs56znV7/mMe+X77Hul7dT rYkCKNVCa/UEUuX6so698xQCetpvp6njvCRdaeBwcvBQVEHF9oDaNzL0ql4DmWfddwbQf mtZdFFc9BEwvo69WEEHbXJZsYGYUND0HTG34vMrhKLPVsUhjy/JSmhMMF09zP+kW29L5A +ekXHCXfhHwJmZLuTmi2Aj06NYI+5jl+YHxiOsTcysED7IjmNY/Q92h0ZkrOWx+YGY8/P LifN84CMMcGJmfRs58Mib22loO7MeA+s+tKeIDvTng0EDV3c21pRUReOVJK2P/rt1bw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794198996; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=uTmIS9aKyym5dH1US1ljpTNJCXSvpIpBaRQvIEMaxHs=; b=aUgqP2mkZv+LP2vk1/imhPAgzvkxSlSJQ8aZILRs9oJ3OwBVE8WSeeWYRSnzAbUiVSRa LCOx/z8wEoostRwZagXERFEh5KmcquZShL1J1PASsDH9fzhw8EFkrfG6AIIoFh0fCEsjS 2p78UhwOsA1MPExzqGgDCDSjjJE3GGPWxHJBRO4MrdYodTvp3veW65P/FUkOy3v7tBAT5 kwyLvB5+gWKOxC1Wy4Ogo1tI/HAQmn2reGue7oyHuwhTPfrBL9slAnoXkmlpKkAQu4b5u NlcK5sjpM+HFZ76gQihurc3L8miOYnrEYNSHC4zzFSjjbvf+H1y50LFa8tQsngsZcaQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Ma6N62v9; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 22545606A31C for ; Mon, 9 Nov 2026 04:36:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Ma6N62v9 Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBA141F0089F; Mon, 9 Nov 2026 04:36:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794198995; bh=uTmIS9aKyym5dH1US1ljpTNJCXSvpIpBaRQvIEMaxHs=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Ma6N62v9XBEMD4MKGpZQhtguYQqVYkJd+iTa7t/DpXBS8g0ZtUEwKBL+08sEzT78g rtnDCxaD+fEJPEqdESt5wJyDWiAcH6Ia6eB7M/sjGJQUA0oJaVGgCwwhc7aHzDzCys 7CK2MaD9eXw8V9K0Pu4bqiGzY9QeDpL/RHfintzQmOv+DHyh7IqgxY9JrAsgTD3Oco YVdKTgRskwuwXWIT2vCdzrxAMVx/LdfqEz4Cfh4JATemMcdSZkRHGoiitmA0kVrVLm /Os2aalndyNDqSi5tJaiHqlHEXV3U4IRX0/7+FGRaNXel8aUv4FFnCRpXjqqUtpORu B+OvYiT4ihCjQ== Date: Mon, 9 Nov 2026 12:16:22 +0800 From: Jisheng Zhang To: Karl Mehltretter Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Charlie Jenkins , Thomas Gleixner , Steven Rostedt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] riscv: entry: Mark ret_from_fork_kernel() and ret_from_fork_user() noinstr Message-ID: References: <20261109041845.33695-1-kmehltretter@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20261109041845.33695-1-kmehltretter@gmail.com> On Mon, Nov 09, 2026 at 05:18:45AM +0100, Karl Mehltretter wrote: > ret_from_fork_kernel() and ret_from_fork_user() are traceable and > return after syscall_exit_to_user_mode() enters the RCU extended > quiescent state via user_enter_irqoff() on NO_HZ_FULL CPUs. When > function_graph tracing is enabled with > FTRACE_VALIDATE_RCU_IS_WATCHING, the return hook runs after RCU stops > watching and triggers the ftrace_return_to_handler() warning. > > Mark ret_from_fork_kernel() and ret_from_fork_user() noinstr. > > Fixes: f955aa8723a6 ("riscv: entry: Convert ret_from_fork() to C") > Signed-off-by: Karl Mehltretter Reviewed-by: Jisheng Zhang > --- > Assisted by an LLM. > > v2: > - Drop instrumentation_begin()/instrumentation_end() around the kernel > thread callback. They only feed objtool's noinstr validation, which > riscv does not have (Jisheng Zhang). ret_from_fork_kernel() and > ret_from_fork_user() disassemble identically to v1 (Clang, defconfig > with NO_HZ_FULL and FUNCTION_GRAPH_TRACER). > > v1: https://lore.kernel.org/r/20261107194931.69176-1-kmehltretter@gmail.com/ > > Tested with v1 on mainline d48723711bae (after v7.4-rc1) under QEMU > riscv64 (-smp 4) with NO_HZ_FULL, FTRACE_VALIDATE_RCU_IS_WATCHING, > PROVE_LOCKING, nohz_full=1-3 rcu_nocbs=1-3 on the kernel command line, > and function_graph tracing during parallel fork bursts across CPUs 0-3. > > arch/riscv/kernel/process.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c > index 34c1d498d1cad..6f2b46d1a8e98 100644 > --- a/arch/riscv/kernel/process.c > +++ b/arch/riscv/kernel/process.c > @@ -225,14 +225,15 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) > return 0; > } > > -asmlinkage void ret_from_fork_kernel(void *fn_arg, int (*fn)(void *), struct pt_regs *regs) > +asmlinkage void noinstr ret_from_fork_kernel(void *fn_arg, int (*fn)(void *), > + struct pt_regs *regs) > { > fn(fn_arg); > > syscall_exit_to_user_mode(regs); > } > > -asmlinkage void ret_from_fork_user(struct pt_regs *regs) > +asmlinkage void noinstr ret_from_fork_user(struct pt_regs *regs) > { > syscall_exit_to_user_mode(regs); > } > > base-commit: d48723711bae9b8cdc56719c448ba42fef28cbee > -- > 2.39.5 (Apple Git-154) >