From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 4163330F540; Sat, 19 Sep 2026 00:35:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789778132; cv=none; b=QRgFlYdmV1K73zcPv76WPY5bH2Ur4RALsTSnSsUY4aCgVzlDOqPH+QsWyPADbiQ4zBKD1/RcB5NT/Ayp7jAvuDGmvgO99SmKzmcUxGCILvDfqPN6Ioff+1tYODd7Ogr7d6CbtqqN5vdqjgk6jO2khx4O+vEBfPkH930FHmQ3szo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789778132; c=relaxed/simple; bh=d4j09ruRw/K4F9/TxKJfNLBZqsAZxaVIe1N9gTmganU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=ctbaZMo8pl7wgP7Zbstz3SyAiY06fB9Y5hVQIz5bG4jvmGNTRVmDwqmXSUJNdgCDg5VTybGk3oGN9ZkKKQAdVlUXwZ36NZd9LHHb6n3BkUELjFAtiWYvaaXLoRRjfVWZW4SixT9Hu4I7WjhkPzu9peP6zgybDar5VQza9sFsHm0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Rty5pnLJ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Rty5pnLJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D06F61F00898; Sat, 19 Sep 2026 00:35:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789778122; bh=5X3n3SbL6yjfY7i0kjbW990bAjkk+TLx5g/Sy6/tvxA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Rty5pnLJFVAaJKVuP5cwQPPwRZtjTi9/fdtQs3nnswFMvtSGjg/MNoMVHlChohH+n Vvl2ViG7/cKh8GJeHWl//SMoX9TygZPHj/kZOcNE3epHtsS0CXaxjS1u/s5Ttfvy1g TN8WQnyd/LJ7zIiaUF2aNAVf8nC1gbep1iCZXWaE9A3h9JgZq8z3zmpbCz+yZQN1F8 /qonuBpRnDx6ULysfQTAVGGsDI0JhoMWoC7Vj2fytn/RpdhAc5Y/rsmOK3khnIiiOO G0PtLJUhG14l8VkVkGDvmRSGozzodj1rpP10UzPYvn2UF5ach8+b/qKivM8GLXuvnd zQMDnEpGjV6FQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 954D4CE178A; Fri, 18 Sep 2026 17:35:22 -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" Subject: [PATCH 02/19] srcutree: Suppress srcu_advance_state() mutex_lock in atomic Date: Fri, 18 Sep 2026 17:35:04 -0700 Message-Id: <20260919003521.3134552-2-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <13d6be93-8d9d-47a2-beb0-99c8a90938d4@paulmck-laptop> References: <13d6be93-8d9d-47a2-beb0-99c8a90938d4@paulmck-laptop> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The new SRCU_READ_FLAVOR_ATOMIC prohibits sleeping in both readers and grace-period waits in order to permit waiting on an SRCU grace period within an OOM notifier. This means that srcu_advance_state() cannot acquire ->srcu_gp_mutex in this case, because mutex_lock() can sleep. This commit therefore adds an is_atomic parameter to srcu_advance_state(). When this parameter is false, current behavior is maintained, in other words, ->srcu_gp_mutex is acquired and released as before. But when this is_atomic parameter is false, the caller is responsible for excluding other callers. Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index d32c374ee72a..dc063eb49b0d 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1941,13 +1941,16 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed); /* * Core SRCU state machine. Push state bits of ->srcu_gp_seq * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has - * completed in that state. + * completed in that state. Set is_atomic to indicate that + * the caller is excluding other calls so that ->srcu_gp_mutex + * is not needed, and to indicate that blocking is forbidden. */ -static void srcu_advance_state(struct srcu_struct *ssp) +static void srcu_advance_state(struct srcu_struct *ssp, bool is_atomic) { int idx; - mutex_lock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_lock(&ssp->srcu_sup->srcu_gp_mutex); /* * Because readers might be delayed for an extended period after @@ -1965,7 +1968,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) { WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq)); raw_spin_unlock_irq_rcu_node(ssp->srcu_sup); - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; } idx = rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)); @@ -1973,7 +1977,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) srcu_gp_start(ssp); raw_spin_unlock_irq_rcu_node(ssp->srcu_sup); if (idx != SRCU_STATE_IDLE) { - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* Someone else started the grace period. */ } } @@ -1981,7 +1986,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN1) { idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]); if (!try_check_zero(ssp, idx, 1)) { - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* readers present, retry later. */ } srcu_flip(ssp); @@ -1999,7 +2005,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) */ idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]); if (!try_check_zero(ssp, idx, 2)) { - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* readers present, retry later. */ } ssp->srcu_sup->srcu_n_exp_nodelay = 0; @@ -2107,7 +2114,7 @@ static void process_srcu(struct work_struct *work) sup = container_of(work, struct srcu_usage, work.work); ssp = sup->srcu_ssp; - srcu_advance_state(ssp); + srcu_advance_state(ssp, false); raw_spin_lock_irq_rcu_node(ssp->srcu_sup); curdelay = srcu_get_delay(ssp); raw_spin_unlock_irq_rcu_node(ssp->srcu_sup); -- 2.40.1