From patchwork Fri Oct 11 17:39:22 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: 13832871 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 5A6241BFDFE; Fri, 11 Oct 2024 17:39:33 +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=1728668373; cv=none; b=ePT9IFfRwROBDYr+oMwk8AK4xA3h6e+K3fzqidS9k8MlsuP99048PidkrH2ZNsIcccKBdGWI+BB4fgc4JQQ17SJxV9NEpLbrIHK26AQc9MepTLUwq5mHXk9aMS1vN8WIwMkEzjHxE3rAUQsPlY/8ShLT/thAvWXqwKZd3lekNQw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728668373; c=relaxed/simple; bh=HtkA9wBw7Sojuw5HhHk7JjMMtDq6tne9Y9iMOe1hFF4=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=K+LpScnC3EGii6NfOgQ9jk15xHn7a3bt7b2U2qE+CJ88WBCNPkSWgElmXpTpvoGWnhbvXHF1QaYwyxVSz9UsxsINhg6DQjbNuCvddhf9guFGb6VxC2Qtd8yhjTEQRqCVO8MSdb2m3KLulUkv7wJr0QIDv7Gj/RwWoKIWGIJ8Np4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ob2jLMg4; 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="Ob2jLMg4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1463FC4CED1; Fri, 11 Oct 2024 17:39:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728668373; bh=HtkA9wBw7Sojuw5HhHk7JjMMtDq6tne9Y9iMOe1hFF4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ob2jLMg4ro6J/JB+s3BjG3i2e2uU3jB6u1ItK0YKX2XGOkVVVX9hAhmGcg9c8NWwI Xzvex1iXc4Lk5/XZJqY4SBRZLRusIroPNFGq4HP024arBgDozXDx5sIiyi7Qfz3H5V AqGTw9+PBZY2HW9KVXz+wk0B9J937n3ZBY8Zxt56SvSzk13n7ZdeSnC32sCYpWtaKK 4dQjAdP/Ahd3RFLqfscl8j/5wDB4oYeiRSTkVgrO5dqzOuKy2yi/3UXlMH4YiqIJDv 96A0e2dynnX0PykpHlWbZnWw1XQuFgoY21amh8HGLPX4/rT5jU2fvKrvijttYqDxCU ctPhmi/K01UGA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id A1D56CE0EBC; Fri, 11 Oct 2024 10:39:32 -0700 (PDT) From: "Paul E. McKenney" To: frederic@kernel.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" , Alexei Starovoitov , Andrii Nakryiko , Peter Zijlstra , Kent Overstreet , bpf@vger.kernel.org Subject: [PATCH v2 rcu 04/13] srcu: Bit manipulation changes for additional reader flavor Date: Fri, 11 Oct 2024 10:39:22 -0700 Message-Id: <20241011173931.2050422-4-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <3b82ac1a-8786-4a27-8eff-ecc67b50dfb6@paulmck-laptop> References: <3b82ac1a-8786-4a27-8eff-ecc67b50dfb6@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 | 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); + 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); }