From nobody Fri Dec 19 00:55:23 2025 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 5D51B1BF6DD for ; Thu, 2 May 2024 21:38:50 +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=1714685932; cv=none; b=EMAkA59XUScSUmKiuDNPadz2tfRXVzIvAbeVQ++wkbtvNdb9jxXGEHvyb00axC3B09RSjhhRLdbbtIoo+eO+0aYyXFgjMn5Kd6KqRV86MJp06WRBqqD8riGyL9orGwQTN4W64myrCeTSpszUSXnSqLy+q04QearH6S9UlNhuYVQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714685932; c=relaxed/simple; bh=V5mxrRSekt1IFCanlpGWcpd6IZlLeeHC7Umzth2wwT4=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=sEYL5qlBrgnunR+gPatdmY3BDu089F1+J0isz7kk+lMlKfCdHFwwxC4zRpcMxtkSet0GZklOoaizHRebMyLO+ckaXptr2m3A918dbTqLMXH3gFImv6VhelwfpeADMTEn0rx8KDmbttzurxoa5CNuKp9aqSpNIYE5Xcg9pLcZn0U= 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=nLlpGNdG; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=LKodxfWh; 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="nLlpGNdG"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="LKodxfWh" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1714685928; 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=t9DvvEOPQaKJAiNHj9V1cPMF/dPZtPshaTQ4VubjDeI=; b=nLlpGNdGe/OTfuVowh0Mr2DmsUboCRFrCjWGT8lEin7RIooN9m+ydrp/nnPHk61VFG1/xO jASLVKqog55kMhugDjewPpTKfFkBe5zapnFctVMZ2NVsRSRiMGaRhsf2DotUttONd/w+CQ 57my5sp5e8DJBJ1VjbB3SgwOreCsG1Lim0iC3wsLVORfJlWDRXXVFtpOJzLKFtuWD2HiSo Jx4uQUS9g44M8JSkpec/EUHzHm3GO2j25GMqRIsBMT7kU7UXoewJ6w8Qof3V18+sVZvpMZ 95BP0xeXRhtsOHlV8ev/EFCr9uTEBtTKN1AuvmOFcXw463BsxMlLRjHRXfmJ7A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1714685928; 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=t9DvvEOPQaKJAiNHj9V1cPMF/dPZtPshaTQ4VubjDeI=; b=LKodxfWhxpWyIDKiMK4KuldsgVPy4jzQeRd9d94+PzXyOq7DRRvCxJbSA+jPobfkLx6D3O 1aYScOgKPWsly9CQ== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: [PATCH printk v5 11/30] nbcon: Provide functions for drivers to acquire console for non-printing Date: Thu, 2 May 2024 23:44:20 +0206 Message-Id: <20240502213839.376636-12-john.ogness@linutronix.de> In-Reply-To: <20240502213839.376636-1-john.ogness@linutronix.de> References: <20240502213839.376636-1-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" Provide functions nbcon_driver_try_acquire() and nbcon_driver_release() to allow drivers to acquire the nbcon console and mark it unsafe for handover/takeover. These functions are to be used by nbcon drivers when performing non-printing activities that should be synchronized with their atomic_write() callback. Signed-off-by: John Ogness Reviewed-by: Petr Mladek --- include/linux/console.h | 2 ++ include/linux/printk.h | 14 +++++++++++ kernel/printk/nbcon.c | 55 ++++++++++++++++++++++++++++++++++++++++- 3 files changed, 70 insertions(+), 1 deletion(-) diff --git a/include/linux/console.h b/include/linux/console.h index aea4f5aa4a45..3c20938f3676 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -304,6 +304,7 @@ struct nbcon_write_context { * * @nbcon_state: State for nbcon consoles * @nbcon_seq: Sequence number of the next record for nbcon to print + * @nbcon_driver_ctxt: Context available for driver non-printing operations * @pbufs: Pointer to nbcon private buffer */ struct console { @@ -399,6 +400,7 @@ struct console { =20 atomic_t __private nbcon_state; atomic_long_t __private nbcon_seq; + struct nbcon_context __private nbcon_driver_ctxt; struct printk_buffers *pbufs; }; =20 diff --git a/include/linux/printk.h b/include/linux/printk.h index d8b3f51d9e98..d0a1106388d1 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -9,6 +9,8 @@ #include #include =20 +struct console; + extern const char linux_banner[]; extern const char linux_proc_banner[]; =20 @@ -193,6 +195,8 @@ void show_regs_print_info(const char *log_lvl); extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold; extern asmlinkage void dump_stack(void) __cold; void printk_trigger_flush(void); +extern bool nbcon_driver_try_acquire(struct console *con); +extern void nbcon_driver_release(struct console *con); #else static inline __printf(1, 0) int vprintk(const char *s, va_list args) @@ -272,6 +276,16 @@ static inline void dump_stack(void) static inline void printk_trigger_flush(void) { } + +static inline bool nbcon_driver_try_acquire(struct console *con) +{ + return false; +} + +static inline void nbcon_driver_release(struct console *con) +{ +} + #endif =20 bool this_cpu_in_panic(void); diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index dd7c3180b335..b8a7e3e136d3 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -5,7 +5,9 @@ #include #include #include +#include #include +#include #include "internal.h" /* * Printk console printing implementation for consoles which does not depe= nd @@ -528,6 +530,7 @@ static struct printk_buffers panic_nbcon_pbufs; * nbcon_context_try_acquire - Try to acquire nbcon console * @ctxt: The context of the caller * + * Context: Under @ctxt->con->device_lock() or local_irq_save(). * Return: True if the console was acquired. False otherwise. * * If the caller allowed an unsafe hostile takeover, on success the @@ -535,7 +538,6 @@ static struct printk_buffers panic_nbcon_pbufs; * in an unsafe state. Otherwise, on success the caller may assume * the console is not in an unsafe state. */ -__maybe_unused static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) { unsigned int cpu =3D smp_processor_id(); @@ -989,3 +991,54 @@ void nbcon_free(struct console *con) =20 con->pbufs =3D NULL; } + +/** + * nbcon_driver_try_acquire - Try to acquire nbcon console and enter unsafe + * section + * @con: The nbcon console to acquire + * + * Context: Under the locking mechanism implemented in + * @con->device_lock() including disabling migration. + * + * Console drivers will usually use their own internal synchronization + * mechasism to synchronize between console printing and non-printing + * activities (such as setting baud rates). However, nbcon console drivers + * supporting atomic consoles may also want to mark unsafe sections when + * performing non-printing activities in order to synchronize against their + * atomic_write() callback. + * + * This function acquires the nbcon console using priority NBCON_PRIO_NORM= AL + * and marks it unsafe for handover/takeover. + */ +bool nbcon_driver_try_acquire(struct console *con) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(con, nbcon_driver_ctxt); + + cant_migrate(); + + memset(ctxt, 0, sizeof(*ctxt)); + ctxt->console =3D con; + ctxt->prio =3D NBCON_PRIO_NORMAL; + + if (!nbcon_context_try_acquire(ctxt)) + return false; + + if (!nbcon_context_enter_unsafe(ctxt)) + return false; + + return true; +} +EXPORT_SYMBOL_GPL(nbcon_driver_try_acquire); + +/** + * nbcon_driver_release - Exit unsafe section and release the nbcon console + * @con: The nbcon console acquired in nbcon_driver_try_acquire() + */ +void nbcon_driver_release(struct console *con) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(con, nbcon_driver_ctxt); + + if (nbcon_context_exit_unsafe(ctxt)) + nbcon_context_release(ctxt); +} +EXPORT_SYMBOL_GPL(nbcon_driver_release); --=20 2.39.2