From nobody Fri Dec 19 00:53:55 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 48C7A1C8FC0 for ; Thu, 2 May 2024 21:38:54 +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=1714685936; cv=none; b=EJt1Th0Rnd5I03kTT6kfzX7KMnNgWKdw9JUJn89MPjp11tVJ0HTnHY+ik4Qih7zYycD+hoKItaNjVMFu4QAuCzIhE5WmqP/N5uqw259702Po4bj6XMR6hi5EVRK3tgb9qGgKpvIaVnAMwlbTSGUxRcKliNQn1bTDHBYtq/II4/Y= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714685936; c=relaxed/simple; bh=gARkG73eQRU8V9yDFnYjNtWOHoOUrDG/qMyvfb3FT5A=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Tjyk738mDNh2D6iJIxDvIxBbkbUW+yaGzzC2rzIDVslceDdUyHUo6+yoqFnAz3bhLylVEzfTg2vJZE3njDvBFQUSM+xaDEjeIvTFTjiHBvVvaE3PNnLYXWMc4HpFJEY+2oi281D9wNIhCwlw4osOhQYkaTs2qNgFrNlhvm+gfz0= 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=Si0FjGbT; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=xnV/4eWX; 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="Si0FjGbT"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="xnV/4eWX" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1714685933; 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=WjNzD/P9+1HhwBtJEEAC1hhuGU7StxseV5FY0ZUbzxw=; b=Si0FjGbTfDhLWv8n4XGqxMj3pt5CGJsUa7NODCfBt1fLhXdaksNkS4LIeZZhcjLPwJ9Qne ZA9dv7PlliiVAx0MpOsr4OA9zMAoeOdn2UlqDBqnV2CCFcj1P7vEKReGeYc/TtFRt5gY2A 3XkgZUUUBHcDPKrEeWm7/uxjSFxGkmiZR6siXvwc53JM9EyZsSdE6yHc9YJpjvq5H8f677 SqbhWDOZ4MRPqCpTCwDjcy60KCtA7XDu/eWXHzbW/cZmt/eB/x8+PWCnNTtP5XKSeppvR0 Bro+Mk4CCA3pTN0BnhEvBvOcTJnMnuIKcTQ4Si6KCajydApAC37JLokHd3SsYA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1714685933; 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=WjNzD/P9+1HhwBtJEEAC1hhuGU7StxseV5FY0ZUbzxw=; b=xnV/4eWXwKv4Woewc7X7tsHGY1gfoaKnp1aglMCfqd9UcUz5F4epk5o8Yo4P0ZfC4MMqRx jRD7gjfDsWunmdAA== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Andrew Morton , Lukas Wunner , Arnd Bergmann , Uros Bizjak , Kefeng Wang Subject: [PATCH printk v5 22/30] printk: nbcon: Add unsafe flushing on panic Date: Thu, 2 May 2024 23:44:31 +0206 Message-Id: <20240502213839.376636-23-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" Add nbcon_atomic_flush_unsafe() to flush all nbcon consoles using the write_atomic() callback and allowing unsafe hostile takeovers. Call this at the end of panic() as a final attempt to flush any pending messages. Note that legacy consoles use unsafe methods for flushing from the beginning of panic (see bust_spinlocks()). Therefore, systems using both legacy and nbcon consoles may still fail to see panic messages due to unsafe legacy console usage. Signed-off-by: John Ogness Reviewed-by: Petr Mladek --- include/linux/printk.h | 5 +++++ kernel/panic.c | 1 + kernel/printk/nbcon.c | 32 +++++++++++++++++++++++++------- 3 files changed, 31 insertions(+), 7 deletions(-) diff --git a/include/linux/printk.h b/include/linux/printk.h index d0a1106388d1..439decc792b6 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -197,6 +197,7 @@ 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); +void nbcon_atomic_flush_unsafe(void); #else static inline __printf(1, 0) int vprintk(const char *s, va_list args) @@ -286,6 +287,10 @@ static inline void nbcon_driver_release(struct console= *con) { } =20 +static inline void nbcon_atomic_flush_unsafe(void) +{ +} + #endif =20 bool this_cpu_in_panic(void); diff --git a/kernel/panic.c b/kernel/panic.c index f22d8f33ea14..c039f8e1ddae 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -453,6 +453,7 @@ void panic(const char *fmt, ...) * Explicitly flush the kernel log buffer one last time. */ console_flush_on_panic(CONSOLE_FLUSH_PENDING); + nbcon_atomic_flush_unsafe(); =20 local_irq_enable(); for (i =3D 0; ; i +=3D PANIC_TIMER_STEP) { diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index abd3835a3466..8f6b3858ab27 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -1044,6 +1044,7 @@ bool nbcon_legacy_emit_next_record(struct console *co= n, bool *handover, * write_atomic() callback * @con: The nbcon console to flush * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers * * Return: 0 if @con was flushed up to @stop_seq Otherwise, error code on * failure. @@ -1062,7 +1063,8 @@ bool nbcon_legacy_emit_next_record(struct console *co= n, bool *handover, * returned, it cannot be expected that the unfinalized record will become * available. */ -static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_= seq) +static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_= seq, + bool allow_unsafe_takeover) { struct nbcon_write_context wctxt =3D { }; struct nbcon_context *ctxt =3D &ACCESS_PRIVATE(&wctxt, ctxt); @@ -1071,6 +1073,7 @@ static int __nbcon_atomic_flush_pending_con(struct co= nsole *con, u64 stop_seq) ctxt->console =3D con; ctxt->spinwait_max_us =3D 2000; ctxt->prio =3D nbcon_get_default_prio(); + ctxt->allow_unsafe_takeover =3D allow_unsafe_takeover; =20 if (!nbcon_context_try_acquire(ctxt)) return -EPERM; @@ -1100,13 +1103,15 @@ static int __nbcon_atomic_flush_pending_con(struct = console *con, u64 stop_seq) * write_atomic() callback * @con: The nbcon console to flush * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers * * This will stop flushing before @stop_seq if another context has ownersh= ip. * That context is then responsible for the flushing. Likewise, if new rec= ords * are added while this context was flushing and there is no other context * to handle the printing, this context must also flush those records. */ -static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_s= eq) +static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_s= eq, + bool allow_unsafe_takeover) { unsigned long flags; int err; @@ -1120,7 +1125,7 @@ static void nbcon_atomic_flush_pending_con(struct con= sole *con, u64 stop_seq) */ local_irq_save(flags); =20 - err =3D __nbcon_atomic_flush_pending_con(con, stop_seq); + err =3D __nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_take= over); =20 local_irq_restore(flags); =20 @@ -1144,8 +1149,9 @@ static void nbcon_atomic_flush_pending_con(struct con= sole *con, u64 stop_seq) * __nbcon_atomic_flush_pending - Flush all nbcon consoles using their * write_atomic() callback * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers */ -static void __nbcon_atomic_flush_pending(u64 stop_seq) +static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_t= akeover) { struct console *con; int cookie; @@ -1163,7 +1169,7 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq) if (nbcon_seq_read(con) >=3D stop_seq) continue; =20 - nbcon_atomic_flush_pending_con(con, stop_seq); + nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover); } console_srcu_read_unlock(cookie); } @@ -1178,7 +1184,19 @@ static void __nbcon_atomic_flush_pending(u64 stop_se= q) */ void nbcon_atomic_flush_pending(void) { - __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb)); + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), false); +} + +/** + * nbcon_atomic_flush_unsafe - Flush all nbcon consoles using their + * write_atomic() callback and allowing unsafe hostile takeovers + * + * Flush the backlog up through the currently newest record. Unsafe hostile + * takeovers will be performed, if necessary. + */ +void nbcon_atomic_flush_unsafe(void) +{ + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), true); } =20 /** @@ -1307,7 +1325,7 @@ void nbcon_driver_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)) { - __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb)); + __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false); } console_srcu_read_unlock(cookie); } --=20 2.39.2