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 0E489288B1; Mon, 14 Oct 2024 16:51:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728924677; cv=none; b=hrd0ILmqSYs+Frbtw6DqsJdQT+8PY4F6ZId1gU1E2CVlDG/RKVgo9+PF0lKCp8q6kHtAjdfPsVSE1egd9J2Va0iCA0PQXyzjnQiq81WZh+C7jJ/8qYIK9NOjzwM0h9/EWNY/PJuU9Jfx/Y4hkQX8vTSeBKGu9oNAYTef9E4fzWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728924677; c=relaxed/simple; bh=HVkCAK28Uz4v2yjt6+6+8HaHLau4B2tiGzMBjwo5yvw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=o4S9qFY5FjZAMxgQKep2h0aU+SMDqyqXW+GO9iJ8pZs7m+/qGk4lf93tJ7ynJF4zszpkoEWAM6wUK6IuyByiWII6xQCjWHEstTptmGE+wUK1FgqHZQadDsqQ14a/4HGxSu07kdeopvzCu8GSZSvHHvA5j8ml/wskq5OrUm8PZU4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eD49wm8e; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eD49wm8e" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F7D9C4CEC3; Mon, 14 Oct 2024 16:51:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728924676; bh=HVkCAK28Uz4v2yjt6+6+8HaHLau4B2tiGzMBjwo5yvw=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=eD49wm8eSZIYMXleMB9YbI5akYYyLT9prVZNXEKSzVFlgu7E66pfEvdB9XbCfwmr9 dSENrcMazgWojRRN8wA8RTkpS20mm4vtSKEpDP79Wc3cq+UFnDuzSfUUMN9a5OxrYD HYOzLf/6sIxa4ayZFNwJbiJvtuYoE53N3n7EiiYU7Updvg68YkfTi4ndvJumsusii5 GS41w7IjAC9oHZUwZoKkH201h7BninzBg/xVVfXlsyyUfOEoOMhKFK+Hf/8xsobphG 6h4ZP8EMejn7b+EMwyNGl3+iwNYGOZ50sBaUpMM6yAa834kd/brgGkM+sDEJGt+ieg kj7DOhEbl84Dg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 3C736CE0B68; Mon, 14 Oct 2024 09:51:16 -0700 (PDT) Date: Mon, 14 Oct 2024 09:51:16 -0700 From: "Paul E. McKenney" To: Neeraj Upadhyay Cc: frederic@kernel.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, Alexei Starovoitov , Andrii Nakryiko , Peter Zijlstra , Kent Overstreet , bpf@vger.kernel.org Subject: Re: [PATCH rcu 04/12] srcu: Bit manipulation changes for additional reader flavor Message-ID: <6f8934c8-8499-48ec-89fa-e3f356fae419@paulmck-laptop> Reply-To: paulmck@kernel.org References: <20241009180719.778285-4-paulmck@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@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: On Mon, Oct 14, 2024 at 02:42:33PM +0530, Neeraj Upadhyay wrote: > On 10/9/2024 11:37 PM, Paul E. McKenney wrote: > > Currently, there are only two flavors of readers, normal and NMI-safe. > > Very straightforward state updates suffice to check for erroneous > > mixing of reader flavors on a given srcu_struct structure. This commit > > upgrades the checking in preparation for the addition of light-weight > > (as in memory-barrier-free) readers. > > > > Signed-off-by: Paul E. McKenney > > Cc: Alexei Starovoitov > > Cc: Andrii Nakryiko > > Cc: Peter Zijlstra > > Cc: Kent Overstreet > > Cc: > > --- > > kernel/rcu/srcutree.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index 18f2eae5e14bd..abe55777c4335 100644 > > --- a/kernel/rcu/srcutree.c > > +++ b/kernel/rcu/srcutree.c > > @@ -462,7 +462,7 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx) > > if (IS_ENABLED(CONFIG_PROVE_RCU)) > > mask = mask | READ_ONCE(cpuc->srcu_reader_flavor); > > } > > - WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask >> 1)), > > + WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)), > > "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp); > > return sum; > > } > > @@ -712,8 +712,9 @@ void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) > > sdp = raw_cpu_ptr(ssp->sda); > > old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor); > > if (!old_reader_flavor_mask) { > > - WRITE_ONCE(sdp->srcu_reader_flavor, reader_flavor_mask); > > - return; > > + old_reader_flavor_mask = cmpxchg(&sdp->srcu_reader_flavor, 0, reader_flavor_mask); > > This looks to be separate independent fix? I would say that it is part of the upgrade. The old logic worked if there are only two flavors, but the cmpxchg() is required for more than two. Thanx, Paul > - Neeraj > > > + if (!old_reader_flavor_mask) > > + return; > > } > > WARN_ONCE(old_reader_flavor_mask != reader_flavor_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_reader_flavor_mask, reader_flavor_mask); > > } >