From nobody Fri Dec 19 08:55:08 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 7EC621B5811 for ; Fri, 30 Aug 2024 15:29:24 +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=1725031766; cv=none; b=kHeFLllKh71/+P3qGh/tpNwlBfXQrt3lK4zGuLF0HuFt92FP36IhbMGjQGSHM6NyIVWy6DpQxVR2NoO9SKV1V0emjMAtSounuQgO4WS8vwpS305WJv5Lsn2wxPmSL6p1OUI8V9jAXrdV8XqPKBAoL+BykVg0xtSfuUymyej6Vpc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725031766; c=relaxed/simple; bh=Z2FzLOhrYPb4SwVt3LRiu+LCw82+Xjl4A5u2HlGOY7g=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=a5BbUeAjg/WwOr4/JahD2pwtQUtWUufVinTGzEkPz+W9Kqk2z+wpkwIUwtkkClEchZjPzYIcYFuJIxzWNWjfSJBQAbSzGP3Fc8awdJEmVIcXladUHa9/MxEvjVih76XGLjrAJCcI7gU9x5RO1bj3wUkSKVpqEoq/qYlXg0VKl+4= 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=Gp37x8Nm; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=WO1vmUGW; 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="Gp37x8Nm"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="WO1vmUGW" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1725031757; 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=Qs4boc16pkWZxtexxvPfNeVBSJ9Cag6SQbs3NPVnzWA=; b=Gp37x8NmtpOR5JxSiHY2bVA2DuFda/MLUxkVy5yGX+pcAd1vcPpv8pL6m8FEj3b0QptkhE LV1h3auXVnm3OsB33EluXT9qws6xwZWViZSGehEo9dpUB7ritEthveqt2Vx8mqHDC2IcF2 +XAMFKAnpGfCde3I+3YhKne71Ql3yCdl0QFjefKqRIyatjJkIMjvxxMroaSe06Q97K3Ind o8xhs/SIeaJNEtSOqSbstobMwSrGqcu1UuiCeCWGaXLUW4P5t5Mwze519eyGB4Xtpr0M0z Ib5PFHDtIS3gcmeduUuQYcE5us+eMYg4LjwZyJ9S+pIiFqJ/4Fpk6IDESm7FWQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1725031757; 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=Qs4boc16pkWZxtexxvPfNeVBSJ9Cag6SQbs3NPVnzWA=; b=WO1vmUGW2q6ICk0vvOsZ96YSVscllFHlVGDAUoGFkFHgF2cHHyjKDLYokQX1deze+03Rr2 q1sJ8M3UtRFJiYDQ== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: [PATCH printk v5 01/17] printk: nbcon: Add function for printers to reacquire ownership Date: Fri, 30 Aug 2024 17:35:00 +0206 Message-Id: <20240830152916.10136-2-john.ogness@linutronix.de> In-Reply-To: <20240830152916.10136-1-john.ogness@linutronix.de> References: <20240830152916.10136-1-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" Since ownership can be lost at any time due to handover or takeover, a printing context _must_ be prepared to back out immediately and carefully. However, there are scenarios where the printing context must reacquire ownership in order to finalize or revert hardware changes. One such example is when interrupts are disabled during printing. No other context will automagically re-enable the interrupts. For this case, the disabling context _must_ reacquire nbcon ownership so that it can re-enable the interrupts. Provide nbcon_reacquire_nobuf() for exactly this purpose. It allows a printing context to reacquire ownership using the same priority as its previous ownership. Note that after a successful reacquire the printing context will have no output buffer because that has been lost. This function cannot be used to resume printing. Signed-off-by: John Ogness Reviewed-by: Petr Mladek --- include/linux/console.h | 6 ++++ kernel/printk/nbcon.c | 74 +++++++++++++++++++++++++++++++++++++---- 2 files changed, 73 insertions(+), 7 deletions(-) diff --git a/include/linux/console.h b/include/linux/console.h index 9a13f91b0c43..88050d30a9cc 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -366,6 +366,10 @@ struct console { * * The callback should allow the takeover whenever it is safe. It * increases the chance to see messages when the system is in trouble. + * If the driver must reacquire ownership in order to finalize or + * revert hardware changes, nbcon_reacquire_nobuf() can be used. + * However, on reacquire the buffer content is no longer available. A + * reacquire cannot be used to resume printing. * * The callback can be called from any context (including NMI). * Therefore it must avoid usage of any locking and instead rely @@ -558,12 +562,14 @@ extern void nbcon_cpu_emergency_exit(void); extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); +extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt); #else static inline void nbcon_cpu_emergency_enter(void) { } static inline void nbcon_cpu_emergency_exit(void) { } static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { = return false; } static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) {= return false; } static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { = return false; } +static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt= ) { } #endif =20 extern int console_set_on_cmdline; diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index 92ac5c590927..d1c640e7e645 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -830,6 +830,19 @@ static bool __nbcon_context_update_unsafe(struct nbcon= _context *ctxt, bool unsaf return nbcon_context_can_proceed(ctxt, &cur); } =20 +static void nbcon_write_context_set_buf(struct nbcon_write_context *wctxt, + char *buf, unsigned int len) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con =3D ctxt->console; + struct nbcon_state cur; + + wctxt->outbuf =3D buf; + wctxt->len =3D len; + nbcon_state_read(con, &cur); + wctxt->unsafe_takeover =3D cur.unsafe_takeover; +} + /** * nbcon_enter_unsafe - Enter an unsafe region in the driver * @wctxt: The write context that was handed to the write function @@ -845,8 +858,12 @@ static bool __nbcon_context_update_unsafe(struct nbcon= _context *ctxt, bool unsaf bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + bool is_owner; =20 - return nbcon_context_enter_unsafe(ctxt); + is_owner =3D nbcon_context_enter_unsafe(ctxt); + if (!is_owner) + nbcon_write_context_set_buf(wctxt, NULL, 0); + return is_owner; } EXPORT_SYMBOL_GPL(nbcon_enter_unsafe); =20 @@ -865,11 +882,43 @@ EXPORT_SYMBOL_GPL(nbcon_enter_unsafe); bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + bool ret; =20 - return nbcon_context_exit_unsafe(ctxt); + ret =3D nbcon_context_exit_unsafe(ctxt); + if (!ret) + nbcon_write_context_set_buf(wctxt, NULL, 0); + return ret; } EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); =20 +/** + * nbcon_reacquire_nobuf - Reacquire a console after losing ownership + * while printing + * @wctxt: The write context that was handed to the write callback + * + * Since ownership can be lost at any time due to handover or takeover, a + * printing context _must_ be prepared to back out immediately and + * carefully. However, there are scenarios where the printing context must + * reacquire ownership in order to finalize or revert hardware changes. + * + * This function allows a printing context to reacquire ownership using the + * same priority as its previous ownership. + * + * Note that after a successful reacquire the printing context will have no + * output buffer because that has been lost. This function cannot be used = to + * resume printing. + */ +void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(wctxt, ctxt); + + while (!nbcon_context_try_acquire(ctxt)) + cpu_relax(); + + nbcon_write_context_set_buf(wctxt, NULL, 0); +} +EXPORT_SYMBOL_GPL(nbcon_reacquire_nobuf); + /** * nbcon_emit_next_record - Emit a record in the acquired context * @wctxt: The write context that will be handed to the write function @@ -895,7 +944,6 @@ static bool nbcon_emit_next_record(struct nbcon_write_c= ontext *wctxt) .pbufs =3D ctxt->pbufs, }; unsigned long con_dropped; - struct nbcon_state cur; unsigned long dropped; =20 /* @@ -930,10 +978,7 @@ static bool nbcon_emit_next_record(struct nbcon_write_= context *wctxt) goto update_con; =20 /* Initialize the write context for driver callbacks. */ - wctxt->outbuf =3D &pmsg.pbufs->outbuf[0]; - wctxt->len =3D pmsg.outbuf_len; - nbcon_state_read(con, &cur); - wctxt->unsafe_takeover =3D cur.unsafe_takeover; + nbcon_write_context_set_buf(wctxt, &pmsg.pbufs->outbuf[0], pmsg.outbuf_le= n); =20 if (con->write_atomic) { con->write_atomic(con, wctxt); @@ -947,6 +992,21 @@ static bool nbcon_emit_next_record(struct nbcon_write_= context *wctxt) return false; } =20 + if (!wctxt->outbuf) { + /* + * Ownership was lost and reacquired by the driver. Handle it + * as if ownership was lost. + */ + nbcon_context_release(ctxt); + return false; + } + + /* + * Ownership may have been lost but _not_ reacquired by the driver. + * This case is detected and handled when entering unsafe to update + * dropped/seq values. + */ + /* * Since any dropped message was successfully output, reset the * dropped count for the console. --=20 2.39.2