Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757605AbaJaJnV (ORCPT ); Fri, 31 Oct 2014 05:43:21 -0400 Received: from mail-wi0-f173.google.com ([209.85.212.173]:59433 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756297AbaJaJnS (ORCPT ); Fri, 31 Oct 2014 05:43:18 -0400 Message-ID: <545359AB.8070503@linaro.org> Date: Fri, 31 Oct 2014 09:43:07 +0000 From: Daniel Thompson User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Stephen Boyd CC: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-serial@vger.kernel.org, Frank Rowand Subject: Re: [PATCH 2/2] tty: serial: msm: Support sysrq on uartDM devices References: <1414606478-13709-1-git-send-email-sboyd@codeaurora.org> <1414606478-13709-3-git-send-email-sboyd@codeaurora.org> <54522163.8030408@linaro.org> <20141031064130.GG12469@codeaurora.org> In-Reply-To: <20141031064130.GG12469@codeaurora.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/10/14 06:41, Stephen Boyd wrote: > On 10/30, Daniel Thompson wrote: >> On 29/10/14 18:14, Stephen Boyd wrote: >>> + r_count = min_t(int, count, sizeof(buf)); >>> + >>> + for (i = 0; i < r_count; i++) { >>> + char flag = TTY_NORMAL; >>> >>> - /* TODO: handle sysrq */ >>> - tty_insert_flip_string(tport, buf, min(count, 4)); >>> - count -= 4; >>> + if (msm_port->break_detected && buf[i] == 0) { >>> + port->icount.brk++; >>> + flag = TTY_BREAK; >>> + msm_port->break_detected = false; >>> + if (uart_handle_break(port)) >>> + continue; >>> + } >>> + >>> + if (!(port->read_status_mask & UART_SR_RX_BREAK)) >>> + flag = TTY_NORMAL; >> >> flag is already known to be TTY_NORMAL. > > Huh? If we detected a break we would set the flag to TTY_BREAK > and if uart_handle_break() returned 0 (perhaps sysrq config is > diasbled) then we would get down here, and then we want to reset > the flag to TTY_NORMAL if the read_status_mask bits indicate that > we want to skip checking for breaks. Otherwise we want to > indicate to the tty layer that it's a break character. Agreed. Sorry for noise. It now reaches the level of silly quibble (meaning I won't bother to raise the issue again if there is a v2 patch) but perhaps updating the flag after the continue would be easier to read. >>> + >>> + spin_unlock(&port->lock); >> >> Is it safe to unlock at this point? count may no longer be valid when we >> return. > > Can you explain further? If it actually isn't valid something > needs to be done. I believe other serial drivers are doing this > sort of thing though so it doesn't seem that uncommon (of course > those drivers could also be broken I suppose). Calling spin_unlock() means we are allow code to alter the state of the UART. In particular the subsequent call to uart_handle_sysrq_char() can make significant changes to the FIFO state (by calling the poll_char functions). Given count is shadowing the FIFO state, when we retake the lock I think it is possible for count to no longer be valid. > >> >> >>> + sysrq = uart_handle_sysrq_char(port, buf[i]); >>> + spin_lock(&port->lock); >>> + if (!sysrq) >>> + tty_insert_flip_char(tport, buf[i], flag); >> >> flag has a constant value here. >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/