Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751990AbaKCKFh (ORCPT ); Mon, 3 Nov 2014 05:05:37 -0500 Received: from mail-wi0-f175.google.com ([209.85.212.175]:46142 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751710AbaKCKFb (ORCPT ); Mon, 3 Nov 2014 05:05:31 -0500 Message-ID: <54575361.1080400@linaro.org> Date: Mon, 03 Nov 2014 10:05:21 +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: frowand.list@gmail.com CC: Stephen Boyd , linux-serial@vger.kernel.org, Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Frank Rowand , linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org 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> <545359AB.8070503@linaro.org> <5453D00F.5000906@gmail.com> In-Reply-To: <5453D00F.5000906@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/10/14 18:08, Frank Rowand wrote: > On 10/31/2014 2:43 AM, Daniel Thompson wrote: >> 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. > > uart_handle_sysrq_char() will not _read_ from the serial port. So it will > not directly modify the FIFO state. poll_char does not read from the FIFO? Since when? SysRq-g will enter cause the system to enter kdb/kgdb from within uart_handle_sysrq_char(). -- 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/