From patchwork Tue Oct 15 16:11:01 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: 13836667 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 5A0E11CB9E2; Tue, 15 Oct 2024 16:11:14 +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=1729008674; cv=none; b=qrsIqPUqkBKajWnQ8dlZ24YsLbsg2clZwhfXayl4TWy+DlfomLM4DBOz3sGU8dZhvPZp79AhXb2QDK6t9uRFarWmceuYdUfaxPREzzbhNkQ6RctW5IJM7ocg9ecwyKPLHpnbf8RKwbOewjKilVY6bd7+OIE0hCRNj8a82D7rD38= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729008674; c=relaxed/simple; bh=HtkA9wBw7Sojuw5HhHk7JjMMtDq6tne9Y9iMOe1hFF4=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=KOyEPZXWwx+6agripVQX0BeCUrfZMVbt1i4UNZ8XRyVjsrlkJfzAsKzD8Kgj1cC+ft9JWqn0g4ra9letBrxuheEq2EE5mYxEUiemS94r27+H/i0JzVYCbK1gk8fwZyuWvUfhbtUocFcKmcEge/M3HN+u2iHzjBryrs56OxMaDEU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BgLXKw6N; 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="BgLXKw6N" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2E766C4CED1; Tue, 15 Oct 2024 16:11:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729008674; bh=HtkA9wBw7Sojuw5HhHk7JjMMtDq6tne9Y9iMOe1hFF4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BgLXKw6N3AW+UE0XMhLDqSIskVLB+HpYigMBdbsRUvuki4N7849L9Qsef8x0PCOuW sVKIg7vmnpeAmr4apZ0rwwbgih3UMRxEGxm32fXVw8nxp8dZKFLGANx//Y4SJRHBDE 4oD7Q6CUrBGrbVavbSKqXTi1I6v0DXk/2RZmeBy/T9zLtg0SLGXPik28l9fEKAduBm SYdgy3BCwcbvD4pui/epYistnTi7xQxmUyRXFVMDnzF/lce7Wdu5mxL0gl0hXoiz0N 33f0I0KfDui+jzdbhJXWmjHbP2rt7xVHU6lGOPpExt9h0DDU87ACcalCaaz7kTQhQ7 fBlLYRICxSdBA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id BC0B7CE0F9A; Tue, 15 Oct 2024 09:11:13 -0700 (PDT) From: "Paul E. McKenney" To: 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 rcu 04/15] srcu: Bit manipulation changes for additional reader flavor Date: Tue, 15 Oct 2024 09:11:01 -0700 Message-Id: <20241015161112.442758-4-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: 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); }