From nobody Sat Feb 7 02:58:53 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 B735C1CD2A for ; Sun, 4 Aug 2024 00:51:54 +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=1722732717; cv=none; b=d2vwW2L1qVuSobye1ZW/AkN2P644qWWNVBCzNkB4EZ41iqkblStdQ6UA/evxEYe8QU6xgVaUr/BUwO41To4ky5jcsx1NImYZZADaBDuCmmw2Hzj0upBpW2HL0YPNvXD2mdX+t3hTsESZrItZUZuDCtifA3OkSTYRpnnlngqRWaM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722732717; c=relaxed/simple; bh=TkTaBS20hEtEiHZ/KnwFlfxd3ElWVcxfaUHrEFUpMig=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=JRmF6jER9l62gooLypr9UPXUSs37gSITQayr4gXGA5deUvWOQAaclDw33KcSNpWevzYUA+EKy8oMbIOF2S0zxUSiJ+sd/kih/f0zHm6gppPhg7h9Z2Wu8a8swZOvWG5iP0wZSWTZcejKH8gWRhcKrzGEybtm0H9XlrZAu6ms5NE= 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=CkwEkpPQ; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=HKq846DA; 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="CkwEkpPQ"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="HKq846DA" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1722732710; 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=5AL01Y9cfZ/udpFpA3TrLaCjrtlq2xqufDMV7WSRCj4=; b=CkwEkpPQKOoieQ1tPCuysetbRd7WTW8HQXATQ8apQ8UOMds7Xalzdrq0576+DF0Nc5sknz saM4kFY/IkQG2J/E67cUMmYv5l2M1hsvwP1nBXwEgu3tfL6yQogtjBbPN4HZQh1VQoR6Xl 3JO998UfazlYTEdxmXctBGV+WZBPhA1QCstQHa9Hbx8t2QjmIRw2ARvRAarh16eweGbqVU R9Fxjih5nHkro5tbxaL7S1lSMedxmn+Z2NJIjfaZ/w0nRSEtZ7TCKDfCoX172HlP4+/GIW LPjg9d0Yq0i2EgPDAdSLZUkaLhXZYeQmWdLz6stIQCm9l3VQJZxNChhYFvN4gg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1722732710; 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=5AL01Y9cfZ/udpFpA3TrLaCjrtlq2xqufDMV7WSRCj4=; b=HKq846DAGZwmhG4S3QsJqZeHbEQQYtgH+dmMFTnlaORYw6nRjfUVEubiN49xtsSNi53c2i 5Zzdqoo/XZLN7MDg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Andrew Morton , Greg Kroah-Hartman , Jani Nikula , Kefeng Wang , Joel Granados , Uros Bizjak Subject: [PATCH printk v7 26/35] printk: nbcon: Add unsafe flushing on panic Date: Sun, 4 Aug 2024 02:57:29 +0206 Message-Id: <20240804005138.3722656-27-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" 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 9687089f5ace..2e083f01f8a3 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -202,6 +202,7 @@ void printk_trigger_flush(void); void console_try_replay_all(void); extern bool nbcon_device_try_acquire(struct console *con); extern void nbcon_device_release(struct console *con); +void nbcon_atomic_flush_unsafe(void); #else static inline __printf(1, 0) int vprintk(const char *s, va_list args) @@ -294,6 +295,10 @@ static inline void nbcon_device_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 f861bedc1925..a58631f42e79 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -457,6 +457,7 @@ 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 269aeed18064..afdb16c1c733 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -1083,6 +1083,7 @@ 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. @@ -1101,7 +1102,8 @@ 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); @@ -1110,6 +1112,7 @@ 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; @@ -1140,13 +1143,15 @@ 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; @@ -1160,7 +1165,7 @@ 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 @@ -1190,8 +1195,9 @@ 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; @@ -1209,7 +1215,7 @@ 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); } @@ -1225,7 +1231,19 @@ 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 /** @@ -1342,7 +1360,7 @@ void nbcon_device_release(struct console *con) if (console_is_usable(con, console_srcu_read_flags(con)) && prb_read_valid(prb, nbcon_seq_read(con), NULL)) { if (!have_boot_console) { - __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb)); + __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false); } else if (!is_printk_legacy_deferred()) { if (console_trylock()) console_unlock(); --=20 2.39.2