From nobody Mon Feb 9 21:03:15 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 E06A422081 for ; Sun, 4 Aug 2024 00:51:55 +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=1722732718; cv=none; b=Ex1tcy/c5Gz/lRed4slkrL3Ps85eODZwbYgfrSbWjN9vHh1XP9KUgswKBIwgHPJ1XLJDazLGgwBi6Qkt/5CP9aEj0sW9seiIgCroj48W50m7OekaqK8nkBA5edrqiAEpkX3z7/Hw34aoN8ZuCs8NYBotNq5QVNnz3adIXcrDCO8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722732718; c=relaxed/simple; bh=02uBS3SK0uI6i7egrbWBVa0YWyj8nlyA26FqupjG2Tk=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=lst/m4J7fi166hiLt7WGW/ujAUBljV6dQLs5r8Ji8MAMCTRFJscK6pawwebQlin3fRGlHcnPg2gJwP2kmG2kOqkZf+TfhXqcByNfDleojdbRs985NF65U6T56vPuBPaFvVJP/dzkWV5i7CS0seBBj/ReTNNYjc0qgaF3+t3rn5M= 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=c8AXeB0J; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=jzWkoBzJ; 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="c8AXeB0J"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="jzWkoBzJ" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1722732711; 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=tSVN0gPPr6tHTy/VzHokuF6g1s3xpImF0LVj64Z+MkU=; b=c8AXeB0JzQbSvM7FxA2ZIWmYXSCJlid4AfTvR0RN/UJh5xSa16Q0nJNBjSqgqvLSH0WHEA B7AyZwPSyIZFOJwnnkSc8jcXieWQejiJw0fxERdUZhDpUgMoDn7vzFnI76a7RoJf304Uy3 Ne2xdhAaoFE6dbWmcLIV8N95PAHLxz+5eK56M7iIkxf/kfbdgRs+ZGPG/MYEQ8TRFBFGM9 cucR8Kgw+2s8yv+AQgc3ILer88d8EGIzo+2B8qIkSHD9CFTmERmkyHo41BbZrdWU8vz9zF UF2l8pGODcALMsPiMbIcWQb1nPgAGip3dYQIE7pJxjIzJUGwSTrb2aEdVHc15g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1722732711; 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=tSVN0gPPr6tHTy/VzHokuF6g1s3xpImF0LVj64Z+MkU=; b=jzWkoBzJburWxIHcNXD9xFnnvJUUfge5mP18/7sHLOTvusDuXBzrrvp5bIKth1boGZ6G7y Kkf1/Sv4JwN307Cg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v7 30/35] printk: Add helper for flush type logic Date: Sun, 4 Aug 2024 02:57:33 +0206 Message-Id: <20240804005138.3722656-31-john.ogness@linutronix.de> In-Reply-To: <20240804005138.3722656-1-john.ogness@linutronix.de> References: <20240804005138.3722656-1-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" There are many call sites where console flushing occur. Depending on the system state and types of consoles, the flush methods to use are different. A flush call site generally must consider: @have_boot_console @have_nbcon_console @have_legacy_console @legacy_allow_panic_sync is_printk_preferred() and take into account the current CPU state: NBCON_PRIO_NORMAL NBCON_PRIO_EMERGENCY NBCON_PRIO_PANIC in order to decide if it should: flush nbcon directly via atomic_write() callback flush legacy directly via console_unlock flush legacy via offload to irq_work All of these call sites use their own logic to make this decision, which is complicated and error prone. Especially later when two more flush methods will be introduced: flush nbcon via offload to kthread flush legacy via offload to kthread Introduce a new internal struct console_flush_type that specifies the flush method(s) that are available for a particular call site to use. Introduce a helper function to fill out console_flush_type to be used for flushing call sites. In many system states it is acceptable to flush legacy directly via console_unlock or via offload to irq_work. The caller must decide which of these methods it prefers. Replace the logic of all flushing call sites to use the new helper. Signed-off-by: John Ogness --- kernel/printk/internal.h | 65 +++++++++++++++++++++++++++++++++++++++ kernel/printk/nbcon.c | 25 ++++++++++++--- kernel/printk/printk.c | 66 ++++++++++++++++++---------------------- 3 files changed, 114 insertions(+), 42 deletions(-) diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index dbda90f0dc08..58eb2a58b07b 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -48,6 +48,7 @@ struct printk_ringbuffer; struct dev_printk_info; =20 extern struct printk_ringbuffer *prb; +extern bool legacy_allow_panic_sync; =20 __printf(4, 0) int vprintk_store(int facility, int level, @@ -156,6 +157,70 @@ static inline bool console_is_usable(struct console *c= on, short flags) { return #endif /* CONFIG_PRINTK */ =20 extern bool have_boot_console; +extern bool have_nbcon_console; +extern bool have_legacy_console; + +/** + * struct console_flush_type - Define available console flush methods + * @nbcon_atomic: Flush directly using nbcon_atomic() callback + * @legacy_direct: Call the legacy loop in this context + * @legacy_offload: Offload the legacy loop into IRQ + * + * Note that the legacy loop also flushes the nbcon consoles. + */ +struct console_flush_type { + bool nbcon_atomic; + bool legacy_direct; + bool legacy_offload; +}; + +/* + * Identify which console flushing methods are available to the context of + * the caller. The caller can then decide which of the available flushing + * methods it will use. + */ +static inline void printk_get_console_flush_type(struct console_flush_type= *ft) +{ + memset(ft, 0, sizeof(*ft)); + + switch (nbcon_get_default_prio()) { + case NBCON_PRIO_NORMAL: + if (have_nbcon_console && !have_boot_console) + ft->nbcon_atomic =3D true; + + if (have_legacy_console || have_boot_console) { + ft->legacy_offload =3D true; + if (!is_printk_legacy_deferred()) + ft->legacy_direct =3D true; + } + break; + + case NBCON_PRIO_PANIC: + /* + * In panic, the nbcon consoles will directly print. But + * only allowed if there are no boot consoles. + */ + if (have_nbcon_console && !have_boot_console) + ft->nbcon_atomic =3D true; + + /* + * In panic, if nbcon atomic printing occurs, the legacy + * consoles must remain silent until explicitly allowed. + * Also, legacy consoles cannot print when deferred. However, + * console_flush_on_panic() will flush them anyway, even if + * unsafe. + */ + if ((legacy_allow_panic_sync || !ft->nbcon_atomic) && + !is_printk_legacy_deferred()) { + ft->legacy_direct =3D true; + } + break; + + default: + WARN_ON_ONCE(1); + break; + } +} =20 extern struct printk_buffers printk_shared_pbufs; =20 diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index afdb16c1c733..9e13327b4fe3 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -1153,6 +1153,7 @@ static int __nbcon_atomic_flush_pending_con(struct co= nsole *con, u64 stop_seq, static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_s= eq, bool allow_unsafe_takeover) { + struct console_flush_type ft; unsigned long flags; int err; =20 @@ -1186,8 +1187,16 @@ static void nbcon_atomic_flush_pending_con(struct co= nsole *con, u64 stop_seq, * other context that will do it. */ if (prb_read_valid(prb, nbcon_seq_read(con), NULL)) { - stop_seq =3D prb_next_reserve_seq(prb); - goto again; + printk_get_console_flush_type(&ft); + /* + * If nbcon_atomic flushing is not available, this printing + * must be occurring via the legacy loop. Let that loop be + * responsible for flushing the new records. + */ + if (ft.nbcon_atomic) { + stop_seq =3D prb_next_reserve_seq(prb); + goto again; + } } } =20 @@ -1344,6 +1353,7 @@ EXPORT_SYMBOL_GPL(nbcon_device_try_acquire); void nbcon_device_release(struct console *con) { struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(con, nbcon_device_ctxt); + struct console_flush_type ft; int cookie; =20 if (!nbcon_context_exit_unsafe(ctxt)) @@ -1359,12 +1369,17 @@ void nbcon_device_release(struct console *con) cookie =3D console_srcu_read_lock(); if (console_is_usable(con, console_srcu_read_flags(con)) && prb_read_valid(prb, nbcon_seq_read(con), NULL)) { - if (!have_boot_console) { + /* + * If nbcon_atomic flushing is not available, fallback to + * using the legacy loop. + */ + printk_get_console_flush_type(&ft); + if (ft.nbcon_atomic) { __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false); - } else if (!is_printk_legacy_deferred()) { + } else if (ft.legacy_direct) { if (console_trylock()) console_unlock(); - } else { + } else if (ft.legacy_offload) { printk_trigger_flush(); } } diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 480c0993abd5..6bed91b5a55b 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -468,14 +468,14 @@ static DEFINE_MUTEX(syslog_lock); * present, it is necessary to perform the console lock/unlock dance * whenever console flushing should occur. */ -static bool have_legacy_console; +bool have_legacy_console; =20 /* * Specifies if an nbcon console is registered. If nbcon consoles are pres= ent, * synchronous printing of legacy consoles will not occur during panic unt= il * the backtrace has been stored to the ringbuffer. */ -static bool have_nbcon_console; +bool have_nbcon_console; =20 /* * Specifies if a boot console is registered. If boot consoles are present, @@ -485,14 +485,6 @@ static bool have_nbcon_console; */ bool have_boot_console; =20 -/* - * Specifies if the console lock/unlock dance is needed for console - * printing. If @have_boot_console is true, the nbcon consoles will - * be printed serially along with the legacy consoles because nbcon - * consoles cannot print simultaneously with boot consoles. - */ -#define printing_via_unlock (have_legacy_console || have_boot_console) - #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); /* All 3 protected by @syslog_lock. */ @@ -2332,7 +2324,7 @@ int vprintk_store(int facility, int level, return ret; } =20 -static bool legacy_allow_panic_sync; +bool legacy_allow_panic_sync; =20 /* * This acts as a one-way switch to allow legacy consoles to print from @@ -2341,9 +2333,12 @@ static bool legacy_allow_panic_sync; */ void printk_legacy_allow_panic_sync(void) { + struct console_flush_type ft; + legacy_allow_panic_sync =3D true; =20 - if (printing_via_unlock && !is_printk_legacy_deferred()) { + printk_get_console_flush_type(&ft); + if (ft.legacy_direct) { if (console_trylock()) console_unlock(); } @@ -2353,8 +2348,8 @@ asmlinkage int vprintk_emit(int facility, int level, const struct dev_printk_info *dev_info, const char *fmt, va_list args) { - bool do_trylock_unlock =3D printing_via_unlock; - bool defer_legacy =3D !do_trylock_unlock; + struct console_flush_type ft; + bool do_trylock_unlock; int printed_len; =20 /* Suppress unimportant messages after panic happens */ @@ -2369,34 +2364,23 @@ asmlinkage int vprintk_emit(int facility, int level, if (other_cpu_in_panic()) return 0; =20 + printk_get_console_flush_type(&ft); + /* If called from the scheduler, we can not call up(). */ if (level =3D=3D LOGLEVEL_SCHED) { level =3D LOGLEVEL_DEFAULT; do_trylock_unlock =3D false; - defer_legacy =3D true; + } else { + do_trylock_unlock =3D ft.legacy_direct; } =20 printk_delay(level); =20 printed_len =3D vprintk_store(facility, level, dev_info, fmt, args); =20 - if (have_nbcon_console && !have_boot_console) { + if (ft.nbcon_atomic) nbcon_atomic_flush_pending(); =20 - /* - * In panic, the legacy consoles are not allowed to print from - * the printk calling context unless explicitly allowed. This - * gives the safe nbcon consoles a chance to print out all the - * panic messages first. This restriction only applies if - * there are nbcon consoles registered and they are allowed to - * flush. - */ - if (this_cpu_in_panic() && !legacy_allow_panic_sync) { - do_trylock_unlock =3D false; - defer_legacy =3D false; - } - } - if (do_trylock_unlock) { /* * The caller may be holding system-critical or @@ -2417,7 +2401,7 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } =20 - if (defer_legacy) + if (!do_trylock_unlock && ft.legacy_offload) defer_console_output(); else wake_up_klogd(); @@ -2776,10 +2760,14 @@ void resume_console(void) */ static int console_cpu_notify(unsigned int cpu) { - if (!cpuhp_tasks_frozen && printing_via_unlock) { - /* If trylock fails, someone else is doing the printing */ - if (console_trylock()) - console_unlock(); + struct console_flush_type ft; + + if (!cpuhp_tasks_frozen) { + printk_get_console_flush_type(&ft); + if (ft.legacy_direct) { + if (console_trylock()) + console_unlock(); + } } return 0; } @@ -3304,6 +3292,7 @@ static void __console_rewind_all(void) */ void console_flush_on_panic(enum con_flush_mode mode) { + struct console_flush_type ft; bool handover; u64 next_seq; =20 @@ -3327,7 +3316,8 @@ void console_flush_on_panic(enum con_flush_mode mode) if (mode =3D=3D CONSOLE_REPLAY_ALL) __console_rewind_all(); =20 - if (!have_boot_console) + printk_get_console_flush_type(&ft); + if (ft.nbcon_atomic) nbcon_atomic_flush_pending(); =20 /* Flush legacy consoles once allowed, even when dangerous. */ @@ -3991,6 +3981,7 @@ static bool __pr_flush(struct console *con, int timeo= ut_ms, bool reset_on_progre { unsigned long timeout_jiffies =3D msecs_to_jiffies(timeout_ms); unsigned long remaining_jiffies =3D timeout_jiffies; + struct console_flush_type ft; struct console *c; u64 last_diff =3D 0; u64 printk_seq; @@ -4004,7 +3995,8 @@ static bool __pr_flush(struct console *con, int timeo= ut_ms, bool reset_on_progre seq =3D prb_next_reserve_seq(prb); =20 /* Flush the consoles so that records up to @seq are printed. */ - if (printing_via_unlock) { + printk_get_console_flush_type(&ft); + if (ft.legacy_direct) { console_lock(); console_unlock(); } --=20 2.39.2