From patchwork Tue Sep 3 16:33:11 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13789073 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 F00AC18C337; Tue, 3 Sep 2024 16:33:19 +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=1725381200; cv=none; b=pRvK5IXtiNwgQfAWmZkIzhT6gMzDhbhyYpZ4ZRbl/4yZ03GLSE9lH5C96gq6qQzIq6uK8YzTia3jfaZ9E0TlGW8WZ3FWj5M6kK98yJ7SntyamzviJy9V+g82l26qiOuhMSrNKgD6UO9mI/QFDs8xlgI8GuuE8INdc/tPk8TUxpY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725381200; c=relaxed/simple; bh=lrdhJdJA4s0Q68tz8/X6z/teMdVY0ZLD1o3u/Im7vbc=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=uFElq7GODsHPaPsJ32VXs6SQG8pEsDyya1wOu8eHrzgtuvMZ+OBorP1X3A83sZjIR8SYgfliacIC4ZPOgwM0adCe3l8Uswu51GmQQHx0xX15OSzo1b+32i0oBkYMdnt97Aqt5wkrIBnzMjCQClnKYXGwn2n5pwAh/CWdlvrDDn4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sUQK0hqW; 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="sUQK0hqW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB4F9C4CECB; Tue, 3 Sep 2024 16:33:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725381199; bh=lrdhJdJA4s0Q68tz8/X6z/teMdVY0ZLD1o3u/Im7vbc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sUQK0hqWHjhN9aKoa4Repr1qNftcp7ydpKncx0makaYsmlxxNjPv55mJQBDwbxo9T aWeqMHa83uUs4/v0FGLp2VjDXMRq3NbJwDPt59qGRSfsvL61QFRCf+W3kUcewoNo/Q CxPfDmqCOh17yHZauRsP0LjfSftLKo2Ho5lHQb1lhzIj9tOK/VW3uCR8IwUMQIBRT7 MnCFqDhnn0XOTRW4wJsepznGB6Fj1UuV5HvecAKg5W0iFmTak4FOcnnsjOKpTKMSws 4gmYcsgXpPus1geBBbWwb3Y7pE8U3xcrM9PFqqORfm686d/5n0YjlEVQYCUF7MIjL+ eAKhlS7UqhRgw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 43E61CE1FB9; Tue, 3 Sep 2024 09:33:19 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, Alexei Starovoitov , Andrii Nakryiko , Peter Zijlstra , Kent Overstreet , bpf@vger.kernel.org, "Paul E. McKenney" Subject: [PATCH rcu 04/11] srcu: Bit manipulation changes for additional reader flavor Date: Tue, 3 Sep 2024 09:33:11 -0700 Message-Id: <20240903163318.480678-4-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <26cddadd-a79b-47b1-923e-9684cd8a7ef4@paulmck-laptop> References: <26cddadd-a79b-47b1-923e-9684cd8a7ef4@paulmck-laptop> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index f259dd8342721..06ade8ca7804f 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 +712,10 @@ 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); + 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); }