From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, BUG6152_INVALID_DATE_TZ_ABSURD,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, INVALID_DATE_TZ_ABSURD,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 172D5C433E0 for ; Wed, 27 Jan 2021 03:31:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6B2E2064B for ; Wed, 27 Jan 2021 03:31:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236144AbhA0Dbj (ORCPT ); Tue, 26 Jan 2021 22:31:39 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:51970 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728972AbhAZVQl (ORCPT ); Tue, 26 Jan 2021 16:16:41 -0500 From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1611695755; 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=1VMLS99e7GLX54QIqDUriax8uAYki14LQK3ROVpMWzE=; b=ljL8X0G1ZPwvxOdtTVGloOYaRW53jC6rmZj2keRVs6WvMv+vr9soJtuXZEsOOzXvqPQlBX 8Kzc27zxN7TtejwIP4ZZB4mHXWg7sVRrCX2btTYjgDreyCgrrAMdKKzPsVYGypd3JvnQ3H azJswOgHaqY3+BbBE06ISKFpvgBGKzmpZ3qgboeAKRSR5BtIN3NXicnYSsmdKbbnahPu6q t52il4U62MfFz9kVJ0FIAr7iQJFd6Nk4tyZH6jyX9Yu/QJfVk2UR0yCHcvUy+LLYaZJhjs QYWkLfRUaHa3gbsOVUohK9mB4CTk7UtH6ttiJSqbsbPOWqw0fhnNe1bHSSWWLg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1611695755; 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=1VMLS99e7GLX54QIqDUriax8uAYki14LQK3ROVpMWzE=; b=k5SQH+KvUmAQOCIU23Arx9ROLaka6zjAdyTxuyXuQxgxFJF6sz5/8eT0BubQPJIZaG7UCS e6vTB7Hx6fV8eQCA== To: Petr Mladek Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk-rework 07/12] printk: add syslog_lock Date: Tue, 26 Jan 2021 22:21:46 +0106 Message-Id: <20210126211551.26536-8-john.ogness@linutronix.de> In-Reply-To: <20210126211551.26536-1-john.ogness@linutronix.de> References: <20210126211551.26536-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The global variables @syslog_seq, @syslog_partial, @syslog_time and write access to @clear_seq are protected by @logbuf_lock. Once @logbuf_lock is removed, these variables will need their own synchronization method. Introduce @syslog_lock for this purpose. Signed-off-by: John Ogness --- kernel/printk/printk.c | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index fe3df16315c0..506d334c065e 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -390,8 +390,12 @@ DEFINE_RAW_SPINLOCK(logbuf_lock); printk_safe_exit_irqrestore(flags); \ } while (0) +/* syslog_lock protects syslog_* variables and write access to clear_seq. */ +static DEFINE_RAW_SPINLOCK(syslog_lock); + #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); +/* All 3 protected by @syslog_lock. */ /* the next printk record to read by syslog(READ) or /proc/kmsg */ static u64 syslog_seq; static size_t syslog_partial; @@ -410,7 +414,7 @@ struct latched_seq { /* * The next printk record to read after the last 'clear' command. There are * two copies (updated with seqcount_latch) so that reads can locklessly - * access a valid value. Writers are synchronized by @logbuf_lock. + * access a valid value. Writers are synchronized by @syslog_lock. */ static struct latched_seq clear_seq = { .latch = SEQCNT_LATCH_ZERO(clear_seq.latch), @@ -465,7 +469,7 @@ bool printk_percpu_data_ready(void) return __printk_percpu_data_ready; } -/* Must be called under logbuf_lock. */ +/* Must be called under syslog_lock. */ static void latched_seq_write(struct latched_seq *ls, u64 val) { raw_write_seqcount_latch(&ls->latch); @@ -1515,7 +1519,9 @@ static int syslog_print(char __user *buf, int size) size_t skip; logbuf_lock_irq(); + raw_spin_lock(&syslog_lock); if (!prb_read_valid(prb, syslog_seq, &r)) { + raw_spin_unlock(&syslog_lock); logbuf_unlock_irq(); break; } @@ -1545,6 +1551,7 @@ static int syslog_print(char __user *buf, int size) syslog_partial += n; } else n = 0; + raw_spin_unlock(&syslog_lock); logbuf_unlock_irq(); if (!n) @@ -1611,8 +1618,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear) break; } - if (clear) + if (clear) { + raw_spin_lock(&syslog_lock); latched_seq_write(&clear_seq, seq); + raw_spin_unlock(&syslog_lock); + } logbuf_unlock_irq(); kfree(text); @@ -1622,7 +1632,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear) static void syslog_clear(void) { logbuf_lock_irq(); + raw_spin_lock(&syslog_lock); latched_seq_write(&clear_seq, prb_next_seq(prb)); + raw_spin_unlock(&syslog_lock); logbuf_unlock_irq(); } @@ -1631,6 +1643,7 @@ int do_syslog(int type, char __user *buf, int len, int source) bool clear = false; static int saved_console_loglevel = LOGLEVEL_DEFAULT; int error; + u64 seq; error = check_syslog_permissions(type, source); if (error) @@ -1648,8 +1661,14 @@ int do_syslog(int type, char __user *buf, int len, int source) return 0; if (!access_ok(buf, len)) return -EFAULT; + + /* Get a consistent copy of @syslog_seq. */ + raw_spin_lock_irq(&syslog_lock); + seq = syslog_seq; + raw_spin_unlock_irq(&syslog_lock); + error = wait_event_interruptible(log_wait, - prb_read_valid(prb, syslog_seq, NULL)); + prb_read_valid(prb, seq, NULL)); if (error) return error; error = syslog_print(buf, len); @@ -1698,6 +1717,7 @@ int do_syslog(int type, char __user *buf, int len, int source) /* Number of chars in the log buffer */ case SYSLOG_ACTION_SIZE_UNREAD: logbuf_lock_irq(); + raw_spin_lock(&syslog_lock); if (syslog_seq < prb_first_valid_seq(prb)) { /* messages are gone, move to first one */ syslog_seq = prb_first_valid_seq(prb); @@ -1724,6 +1744,7 @@ int do_syslog(int type, char __user *buf, int len, int source) } error -= syslog_partial; } + raw_spin_unlock(&syslog_lock); logbuf_unlock_irq(); break; /* Size of the log buffer */ @@ -2965,7 +2986,12 @@ void register_console(struct console *newcon) */ exclusive_console = newcon; exclusive_console_stop_seq = console_seq; + + /* Get a consistent copy of @syslog_seq. */ + raw_spin_lock(&syslog_lock); console_seq = syslog_seq; + raw_spin_unlock(&syslog_lock); + logbuf_unlock_irqrestore(flags); } console_unlock(); -- 2.20.1