From nobody Wed Sep 10 02:55:22 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D13FC0015E for ; Fri, 28 Jul 2023 00:02:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230341AbjG1ACw (ORCPT ); Thu, 27 Jul 2023 20:02:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46660 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229771AbjG1ACm (ORCPT ); Thu, 27 Jul 2023 20:02:42 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6C3F30FB for ; Thu, 27 Jul 2023 17:02:39 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1690502557; 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=zQ+5GFgvTYBrgG/gdG5LVsZvzCc8vSNhvk0jKBm+CCo=; b=uIIPXliW+A6EgH2lwlEr1gJeNeuAXEsY3WO8uFMJrkYscgESGYB+lhCWaXYRoO58CZTnwa l2h5meAY/H5+TL6R+znFVDl5drSt18/dXv6TAe+UVeHxR2PgeahI3Lnaa4LhWkZiSJ0LU2 uv3vj+qKYERD3I4r+VAu/JikZ3lt+entASHR2xUl0GoFVbAlD65foUX1RSIJLB+5nh2J9V 3OryIMUi0T3CiF4zkHiEa5CycdmdEEZo0WdOvKwXmgWdGnu2OqTQUjqZUXFP3+MtQ9oYzX SAolP93EPQnjW+o6e92Ymeo7NalwvY2idruM/kv5lv5Cghv94bxOSGcIU867ww== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1690502557; 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=zQ+5GFgvTYBrgG/gdG5LVsZvzCc8vSNhvk0jKBm+CCo=; b=gPSHpsOiX/R3mhLQZAseHTJvjSYroz99Pnd9DUbBZu5UhZCYBRgMi4zQkGQuBcD/ufPblk pVxwVBqn/ssCI9CA== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: [PATCH printk v2 4/8] printk: nbcon: Add buffer management Date: Fri, 28 Jul 2023 02:08:29 +0206 Message-Id: <20230728000233.50887-5-john.ogness@linutronix.de> In-Reply-To: <20230728000233.50887-1-john.ogness@linutronix.de> References: <20230728000233.50887-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Thomas Gleixner In case of hostile takeovers it must be ensured that the previous owner cannot scribble over the output buffer of the emergency/panic context. This is achieved by: - Adding a global output buffer instance for the panic context. This is the only situation where hostile takeovers can occur and there is always at most 1 panic context. - Allocating an output buffer per console upon console registration. This buffer is used by the console owner when not in panic context. - Choosing the appropriate buffer is handled in the acquire/release functions. Co-developed-by: John Ogness Signed-off-by: John Ogness Signed-off-by: Thomas Gleixner (Intel) Reviewed-by: Petr Mladek --- include/linux/console.h | 7 +++++++ kernel/printk/internal.h | 6 ++++++ kernel/printk/printk.c | 6 ------ kernel/printk/printk_nbcon.c | 26 ++++++++++++++++++++++++-- 4 files changed, 37 insertions(+), 8 deletions(-) diff --git a/include/linux/console.h b/include/linux/console.h index e06cd1ce3e82..d2bcd2c190a7 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -233,6 +233,7 @@ enum nbcon_prio { }; =20 struct console; +struct printk_buffers; =20 /** * struct nbcon_context - Context for console acquire/release @@ -242,6 +243,7 @@ struct console; * @unsafe: This context is in an unsafe section * @hostile: Acquire console by hostile takeover * @takeover_unsafe: Acquire console by hostile takeover even if unsafe + * @pbufs: Pointer to the text buffer for this context */ struct nbcon_context { /* members set by caller */ @@ -251,6 +253,9 @@ struct nbcon_context { unsigned int unsafe : 1; unsigned int hostile : 1; unsigned int takeover_unsafe : 1; + + /* members set by acquire */ + struct printk_buffers *pbufs; }; =20 /** @@ -274,6 +279,7 @@ struct nbcon_context { * @node: hlist node for the console list * * @nbcon_state: State for nbcon consoles + * @pbufs: Pointer to nbcon private buffer */ struct console { char name[16]; @@ -296,6 +302,7 @@ struct console { =20 /* nbcon console specific members */ atomic_t __private nbcon_state; + struct printk_buffers *pbufs; }; =20 #ifdef CONFIG_LOCKDEP diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 655810f2976e..0f2be350600e 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -13,6 +13,12 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, i= nt write, #define printk_sysctl_init() do { } while (0) #endif =20 +#define con_printk(lvl, con, fmt, ...) \ + printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \ + (con->flags & CON_NBCON) ? "" : "legacy ", \ + (con->flags & CON_BOOT) ? "boot" : "", \ + con->name, con->index, ##__VA_ARGS__) + #ifdef CONFIG_PRINTK =20 #ifdef CONFIG_PRINTK_CALLER diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 98b4854c81ea..582552a96c57 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3359,12 +3359,6 @@ static void try_enable_default_console(struct consol= e *newcon) newcon->flags |=3D CON_CONSDEV; } =20 -#define con_printk(lvl, con, fmt, ...) \ - printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \ - (con->flags & CON_NBCON) ? "" : "legacy ", \ - (con->flags & CON_BOOT) ? "boot" : "", \ - con->name, con->index, ##__VA_ARGS__) - static void console_init_seq(struct console *newcon, bool bootcon_register= ed) { struct console *con; diff --git a/kernel/printk/printk_nbcon.c b/kernel/printk/printk_nbcon.c index b0acde0cb949..39fa64891ec6 100644 --- a/kernel/printk/printk_nbcon.c +++ b/kernel/printk/printk_nbcon.c @@ -5,6 +5,7 @@ #include #include #include +#include #include "internal.h" /* * Printk console printing implementation for consoles that do not depend = on @@ -20,6 +21,9 @@ * region and aborts the operation if it detects a takeover. * * In case of panic the nesting context can take over the console forceful= ly. + * If the interrupted context touches the assigned record buffer after + * takeover, it does not cause harm because the interrupting single panic + * context is assigned its own panic record buffer. * * A concurrent writer on a different CPU with a higher priority can reque= st * to take over the console by: @@ -356,6 +360,8 @@ static int nbcon_context_try_acquire_hostile(struct nbc= on_context *ctxt, return 0; } =20 +static struct printk_buffers panic_nbcon_pbufs; + /** * nbcon_context_try_acquire - Try to acquire nbcon console * @ctxt: The context of the caller @@ -372,7 +378,6 @@ static int nbcon_context_try_acquire_hostile(struct nbc= on_context *ctxt, __maybe_unused static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) { - __maybe_unused unsigned int cpu =3D smp_processor_id(); struct console *con =3D ctxt->console; struct nbcon_state cur; @@ -471,6 +476,13 @@ static bool nbcon_context_try_acquire(struct nbcon_con= text *ctxt) ctxt->hostile =3D 0; ctxt->takeover_unsafe =3D 0; } + + /* Assign the appropriate buffer for this context. */ + if (atomic_read(&panic_cpu) =3D=3D cpu) + ctxt->pbufs =3D &panic_nbcon_pbufs; + else + ctxt->pbufs =3D con->pbufs; + return true; } =20 @@ -509,7 +521,7 @@ static void nbcon_context_release(struct nbcon_context = *ctxt) nbcon_state_read(con, &cur); do { if (!nbcon_owner_matches(&cur, cpu, ctxt->prio)) - return; + break; =20 new.atom =3D cur.atom; new.prio =3D NBCON_PRIO_NONE; @@ -521,6 +533,8 @@ static void nbcon_context_release(struct nbcon_context = *ctxt) */ =20 } while (!nbcon_state_try_cmpxchg(con, &cur, &new)); + + ctxt->pbufs =3D NULL; } =20 /** @@ -534,6 +548,12 @@ bool nbcon_init(struct console *con) { struct nbcon_state state =3D { }; =20 + con->pbufs =3D kmalloc(sizeof(*con->pbufs), GFP_KERNEL); + if (!con->pbufs) { + con_printk(KERN_ERR, con, "failed to allocate printing buffer\n"); + return false; + } + nbcon_state_set(con, &state); return true; } @@ -547,4 +567,6 @@ void nbcon_cleanup(struct console *con) struct nbcon_state state =3D { }; =20 nbcon_state_set(con, &state); + kfree(con->pbufs); + con->pbufs =3D NULL; } --=20 2.39.2