Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946152AbaGRV3B (ORCPT ); Fri, 18 Jul 2014 17:29:01 -0400 Received: from mail-ig0-f173.google.com ([209.85.213.173]:33592 "EHLO mail-ig0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946008AbaGRV2N (ORCPT ); Fri, 18 Jul 2014 17:28:13 -0400 From: Alex Elder To: akpm@linux-foundation.org Cc: kay@vrfy.org, pmladek@suse.cz, bp@suse.de, john.stultz@linaro.org, jack@suse.cz, linux-kernel@vger.kernel.org Subject: [PATCH v4 4/7] printk: honor LOG_PREFIX in devkmsg_read() Date: Fri, 18 Jul 2014 16:28:02 -0500 Message-Id: <1405718885-11227-5-git-send-email-elder@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1405718885-11227-1-git-send-email-elder@linaro.org> References: <1405718885-11227-1-git-send-email-elder@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In devkmsg_read(), a variable "cont" holds a character that's used to indicate whether a given log line is a "continuation", that is, whether a log record should be merged with the one before or after it. If a record should be merged with its successor (but not its predecessor) that character is 'c'. And the line following such a 'c' log record is normally marked with a '+' to show it is continues its predecessor. Any other cases are marked '-', indicating the log record stands on its own. There is an exception. If a log record is marked LOG_PREFIX, it indicates that this record represents a new log entry, implicitly terminating the predecessor--even if the predecessor would otherwise have been continued. So a record marked LOG_PREFIX (that is not also marked LOG_CONT) should have '-' for its "cont" variable. The logic that determines this "continuation" character has a bug that gets that exceptional case wrong. The specific case that produces the wrong result is when all of these conditions are non-zero: user->prev & LOG_CONT msg->flags & LOG_PREFIX msg->flags & LOG_CONT The bug is that despite the message's LOG_PREFIX flag, the "cont" character is getting set to '+' rather than 'c'. The problem is that the message's LOG_PREFIX flag is getting ignored if its LOG_CONT flag is also set. Rearrange the logic here to produce the correct result. The following table concisely defines the problem: prev | msg | msg ||"cont" CONT |PREFIX| CONT || char ------+------+------++------ clear| clear| clear|| '-' clear| clear| set || 'c' clear| set | clear|| '-' clear| set | set || 'c' set | clear| clear|| '+' set | clear| set || '+' set | set | clear|| '-' set | set | set || '+' <-- should be 'c' Signed-off-by: Alex Elder Reviewed-by: Petr Mladek --- kernel/printk/printk.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index ad644b3..f8ab63c 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -572,7 +572,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, struct printk_log *msg; u64 ts_usec; size_t i; - char cont = '-'; + char cont; size_t len; ssize_t ret; @@ -619,11 +619,12 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, * better readable output. 'c' in the record flags mark the first * fragment of a line, '+' the following. */ - if (msg->flags & LOG_CONT && !(user->prev & LOG_CONT)) - cont = 'c'; - else if ((msg->flags & LOG_CONT) || - ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))) + if ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX)) cont = '+'; + else if (msg->flags & LOG_CONT) + cont = 'c'; + else + cont = '-'; len = sprintf(user->buf, "%u,%llu,%llu,%c;", (msg->facility << 3) | msg->level, -- 1.9.1 -- 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/