From nobody Fri Feb 13 03:12:01 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 910F313CF96 for ; Mon, 3 Jun 2024 23:24:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717457101; cv=none; b=qD9UDgj3NOQDj2LDxixxdd4a8LvGr/mvYSHkVfWJD3Z8D3EemUShygd63IwT3Z/F+kVvmRmCX4RwcvJ7rvyJOaPOWgDpUTQfVZo7mTFBByGkRHaVmmDAXGniNSWHz9nV4kEQtcZiUPnJUuUrYsTpx2/R/7kCSJ8C2u+GT1FEt34= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717457101; c=relaxed/simple; bh=h2xMza0pIQO539SBEF2bOG10SNxaO64Y36tbIZ1NJiw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=OTXbpkaTxNx4y548u+vHVp9nLgV0SQ9jeekcq3Z4xOCneG6sOALJ6bm1gg7z0jff0+qQz3amKW4A9v3VOrAustkZH91hR8kJ6HpCsP+4wfnFKv6cBw46u4UPK58ovLbqZTvfoKJT/c8B/nvoK8w8ZXM3TPhA7U7wxNwf5YZ6VL0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=y8Ji3U76; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=1jC6egg5; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="y8Ji3U76"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="1jC6egg5" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1717457097; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pr40aimvVoxs/7225bC4/W64BDXKDTy5/ujSTndIDGE=; b=y8Ji3U76CjKRLf3D9VTzoCW2CEw+//r5l49+k97RHLBIIMjJamgP6u1SnM/tVxw66knEyQ m5Me5QlmXTbCT0JALBFys3p37g6oP/Z4wJ0V3fkJSPWCspKk9kv4+ef5dyP74r9AUFsWNK Z1V8c8f0iGTqoYP5KVYYPF/dQ6HXxyMgN0lIOplS3e64Y+d6NgXMes4sqS4HBRbmlDMy0Y gykfkQ0E9okxEzhxKeLV79MG2x0pU+fPXXmFptezobWhNKMSu+yFDyduAUrBzc1yL0yd4c CazzkcJyOH2g6sScPu7LUkKfkrJ2RB7vmbEgrVdjQOixVP1mVSc66lxixT8Kog== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1717457097; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pr40aimvVoxs/7225bC4/W64BDXKDTy5/ujSTndIDGE=; b=1jC6egg58HtK5mqFOWq9YgaeY2QhFJsGl9NuJnAEnzv+AGEOGCzE/gpNhG4qWw8HMiU2jY 9gi2mfcZAs65aCBQ== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , "Paul E. McKenney" Subject: [PATCH printk v2 07/18] printk: nbcon: Add printer thread wakeups Date: Tue, 4 Jun 2024 01:30:42 +0206 Message-Id: <20240603232453.33992-8-john.ogness@linutronix.de> In-Reply-To: <20240603232453.33992-1-john.ogness@linutronix.de> References: <20240603232453.33992-1-john.ogness@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Thomas Gleixner Add a function to wakeup the printer threads. The printer threads are woken when: - a record is added to the printk ringbuffer - consoles are resumed - triggered via printk_trigger_flush() - consoles should be replayed via sysrq The actual waking is performed via irq_work so that the function can be called from any context. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) --- include/linux/console.h | 3 +++ kernel/printk/internal.h | 1 + kernel/printk/nbcon.c | 56 ++++++++++++++++++++++++++++++++++++++++ kernel/printk/printk.c | 8 ++++++ 4 files changed, 68 insertions(+) diff --git a/include/linux/console.h b/include/linux/console.h index 4de42ec1527c..adcc1a74aeee 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -16,6 +16,7 @@ =20 #include #include +#include #include #include #include @@ -327,6 +328,7 @@ struct nbcon_write_context { * @pbufs: Pointer to nbcon private buffer * @kthread: Printer kthread for this console * @rcuwait: RCU-safe wait object for @kthread waking + * @irq_work: Defer @kthread waking to IRQ work context */ struct console { char name[16]; @@ -446,6 +448,7 @@ struct console { struct printk_buffers *pbufs; struct task_struct *kthread; struct rcuwait rcuwait; + struct irq_work irq_work; }; =20 #ifdef CONFIG_LOCKDEP diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 243d3d3bc889..b2b5c10a4321 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -93,6 +93,7 @@ void nbcon_atomic_flush_pending(void); bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, int cookie); void nbcon_kthread_create(struct console *con); +void nbcon_wake_threads(void); =20 /* * Check if the given console is currently capable and allowed to print diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index 4200953d368e..4ab47cc014a3 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -1058,6 +1058,61 @@ static int nbcon_kthread_func(void *__console) goto wait_for_event; } =20 +/** + * nbcon_irq_work - irq work to wake printk thread + * @irq_work: The irq work to operate on + */ +static void nbcon_irq_work(struct irq_work *irq_work) +{ + struct console *con =3D container_of(irq_work, struct console, irq_work); + + nbcon_kthread_wake(con); +} + +static inline bool rcuwait_has_sleeper(struct rcuwait *w) +{ + bool has_sleeper; + + rcu_read_lock(); + /* + * Guarantee any new records can be seen by tasks preparing to wait + * before this context checks if the rcuwait is empty. + * + * This full memory barrier pairs with the full memory barrier within + * set_current_state() of ___rcuwait_wait_event(), which is called + * after prepare_to_rcuwait() adds the waiter but before it has + * checked the wait condition. + * + * This pairs with nbcon_kthread_func:A. + */ + smp_mb(); /* LMM(rcuwait_has_sleeper:A) */ + has_sleeper =3D !!rcu_dereference(w->task); + rcu_read_unlock(); + + return has_sleeper; +} + +/** + * nbcon_wake_threads - Wake up printing threads using irq_work + */ +void nbcon_wake_threads(void) +{ + struct console *con; + int cookie; + + cookie =3D console_srcu_read_lock(); + for_each_console_srcu(con) { + /* + * Only schedule irq_work if the printing thread is + * actively waiting. If not waiting, the thread will + * notice by itself that it has work to do. + */ + if (con->kthread && rcuwait_has_sleeper(&con->rcuwait)) + irq_work_queue(&con->irq_work); + } + console_srcu_read_unlock(cookie); +} + /* Track the nbcon emergency nesting per CPU. */ static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting); static unsigned int early_nbcon_pcpu_emergency_nesting __initdata; @@ -1558,6 +1613,7 @@ void nbcon_init(struct console *con, u64 init_seq) BUG_ON(!con->pbufs); =20 rcuwait_init(&con->rcuwait); + init_irq_work(&con->irq_work, nbcon_irq_work); nbcon_seq_force(con, init_seq); nbcon_state_set(con, &state); } diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index a2c4fe3d21cc..457c01311a95 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2402,6 +2402,8 @@ asmlinkage int vprintk_emit(int facility, int level, } } =20 + nbcon_wake_threads(); + if (do_trylock_unlock) { /* * The caller may be holding system-critical or @@ -2708,6 +2710,10 @@ void resume_console(void) */ synchronize_srcu(&console_srcu); =20 + /* + * Since this runs in task context, wake the threaded printers + * directly rather than scheduling irq_work to do it. + */ cookie =3D console_srcu_read_lock(); for_each_console_srcu(con) { flags =3D console_srcu_read_flags(con); @@ -4178,6 +4184,7 @@ void defer_console_output(void) =20 void printk_trigger_flush(void) { + nbcon_wake_threads(); defer_console_output(); } =20 @@ -4513,6 +4520,7 @@ void console_try_replay_all(void) { if (console_trylock()) { __console_rewind_all(); + nbcon_wake_threads(); /* Consoles are flushed as part of console_unlock(). */ console_unlock(); } --=20 2.39.2