From patchwork Fri Jan 10 21:38:22 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Anderson X-Patchwork-Id: 856515 Received: from out-170.mta0.migadu.com (out-170.mta0.migadu.com [91.218.175.170]) (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 DA53C18C03A for ; Fri, 10 Jan 2025 21:38:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736545127; cv=none; b=Cchq6MIFoOWz8uvMJPdkSTWqD2WAvsxGIzkdIuakNupn/Uw6sFSd4AiRUhma9h15oRYrA2nvotZTtvc6y9QwalgTmUF4F79CkHRCT/lz9sSqk/4QulOgXJeXT7mlcCPth8kdbNjhpccN/b+WsXRaUOEaUumVzYdzByMTYYDmtkM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736545127; c=relaxed/simple; bh=uN8OvW217jnJrGT746idFk71yViCEnErL4OQOhqSQZE=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=pQEkV+Gnw0moCfFiOtOt2vjvxjpX25nvNNCH+V7jje58QoTmhSM/aKoQtmbT1TxC2kvAI54kIaGCL+I3irBDp7z3WV92uZ4SP496WvNpv8XKeb8qhD3HaOEMSQUaKVQ7lumLr26ijTioG/uivH7BkbXHDfXrKbqd1hNlZuGdOyk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Wva81Aww; arc=none smtp.client-ip=91.218.175.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Wva81Aww" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1736545109; 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; bh=iC3k1SZlNlarqOZELintr0r8/tkyMFglXXS2+edHzKk=; b=Wva81Awwv8ENbIE/bgyPENEqbHTNL7iwNmGOtP50PP3xoef58qXCG690ciwFORmKWOkdrA FNQQVJ3dEzFR5l/R2SluGnP4Br//1R/g2BpGUpQFhiM0+NiikXAjGI5g6lNrvm9Vedt/b/ wGU6ue67daWJX2W5IWpOviA0bntRhrY= From: Sean Anderson To: Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org Cc: Manikanta Guntupalli , linux-arm-kernel@lists.infradead.org, John Ogness , linux-kernel@vger.kernel.org, Michal Simek , Thomas Gleixner , Sean Anderson , stable@vger.kernel.org Subject: [PATCH] tty: xilinx_uartps: split sysrq handling Date: Fri, 10 Jan 2025 16:38:22 -0500 Message-Id: <20250110213822.2107462-1-sean.anderson@linux.dev> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT lockdep detects the following circular locking dependency: CPU 0 CPU 1 ========================== ============================ cdns_uart_isr() printk() uart_port_lock(port) console_lock() cdns_uart_console_write() if (!port->sysrq) uart_port_lock(port) uart_handle_break() port->sysrq = ... uart_handle_sysrq_char() printk() console_lock() The fixed commit attempts to avoid this situation by only taking the port lock in cdns_uart_console_write if port->sysrq unset. However, if (as shown above) cdns_uart_console_write runs before port->sysrq is set, then it will try to take the port lock anyway. This may result in a deadlock. Fix this by splitting sysrq handling into two parts. We use the prepare helper under the port lock and defer handling until we release the lock. Fixes: 74ea66d4ca06 ("tty: xuartps: Improve sysrq handling") Signed-off-by: Sean Anderson Cc: # c980248179d: serial: xilinx_uartps: Use port lock wrappers --- drivers/tty/serial/xilinx_uartps.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c index beb151be4d32..92ec51870d1d 100644 --- a/drivers/tty/serial/xilinx_uartps.c +++ b/drivers/tty/serial/xilinx_uartps.c @@ -287,7 +287,7 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus) continue; } - if (uart_handle_sysrq_char(port, data)) + if (uart_prepare_sysrq_char(port, data)) continue; if (is_rxbs_support) { @@ -495,7 +495,7 @@ static irqreturn_t cdns_uart_isr(int irq, void *dev_id) !(readl(port->membase + CDNS_UART_CR) & CDNS_UART_CR_RX_DIS)) cdns_uart_handle_rx(dev_id, isrstatus); - uart_port_unlock(port); + uart_unlock_and_check_sysrq(port); return IRQ_HANDLED; } @@ -1380,9 +1380,7 @@ static void cdns_uart_console_write(struct console *co, const char *s, unsigned int imr, ctrl; int locked = 1; - if (port->sysrq) - locked = 0; - else if (oops_in_progress) + if (oops_in_progress) locked = uart_port_trylock_irqsave(port, &flags); else uart_port_lock_irqsave(port, &flags);