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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,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 A2285C43332 for ; Thu, 18 Feb 2021 09:40:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C6DA64E68 for ; Thu, 18 Feb 2021 09:40:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231863AbhBRJaN (ORCPT ); Thu, 18 Feb 2021 04:30:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51534 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230482AbhBRITT (ORCPT ); Thu, 18 Feb 2021 03:19:19 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 815F4C061793 for ; Thu, 18 Feb 2021 00:18:24 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1613636301; 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=t0o+vVb+hTfMlXvF3+iaxcbhq0mmLxZ4H2QjBu2ZRN0=; b=4nmWi/orwLIPwtbvDT/p+b2A24gkcN5aP5N4ez8+TfTZXAAijZf1GjMbhtQ/RT0JbTJqYS 5G4XcE3JtKnzozYWvNMg8IlP51btZN1khk886PftbQTKn2gGlaNRtghu4TK2CyQO/jS7CA a13C0HnjG5rxlq1127eFETY2+O7Vb7837m4f96nE4JgBjSDGtoEXkJWfaFRaGnUtYT+vkQ vCN1wJFeMfc8ql2D+eUGNPzK+U1y8IUcBm+VSOZBTcKhxaozix8ggqo8Yll7EKnXQmpJvi kwhWPNw2plwQJhsSmintq1/o8DZ9nE4VuKXH+TP+ereKmKfbED9HAAHGwtaJEA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1613636301; 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=t0o+vVb+hTfMlXvF3+iaxcbhq0mmLxZ4H2QjBu2ZRN0=; b=Hp5DkfmsbUg5/KctDIEV/jdapDMBLchsDCPt7jai9aWpOHs7EnMD3MPYijJl+GER9/24RL n6Q8x0x6JvSO6tAw== To: Petr Mladek Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk-rework 08/14] printk: add syslog_lock Date: Thu, 18 Feb 2021 09:18:11 +0100 Message-Id: <20210218081817.28849-9-john.ogness@linutronix.de> In-Reply-To: <20210218081817.28849-1-john.ogness@linutronix.de> References: <20210218081817.28849-1-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. @syslog_lock is a raw_spin_lock for now. This simplifies the transition to removing @logbuf_lock. Once @logbuf_lock and the safe buffers are removed, @syslog_lock can change to spin_lock. Signed-off-by: John Ogness --- kernel/printk/printk.c | 41 +++++++++++++++++++++++++++++++++++++---- 1 file changed, 37 insertions(+), 4 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 20c21a25143d..401df370832b 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), @@ -470,7 +474,7 @@ 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); @@ -1530,7 +1534,9 @@ 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; } @@ -1560,6 +1566,7 @@ 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) @@ -1626,8 +1633,11 @@ 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); @@ -1637,10 +1647,24 @@ 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(); } +/* Return a consistent copy of @syslog_seq. */ +static u64 read_syslog_seq_irq(void) +{ + u64 seq; + + raw_spin_lock_irq(&syslog_lock); + seq = syslog_seq; + raw_spin_unlock_irq(&syslog_lock); + + return seq; +} + int do_syslog(int type, char __user *buf, int len, int source) { struct printk_info info; @@ -1664,8 +1688,9 @@ int do_syslog(int type, char __user *buf, int len, int source) return 0; if (!access_ok(buf, len)) return -EFAULT; + error = wait_event_interruptible(log_wait, - prb_read_valid(prb, syslog_seq, NULL)); + prb_read_valid(prb, read_syslog_seq_irq(), NULL)); if (error) return error; error = syslog_print(buf, len); @@ -1714,8 +1739,10 @@ 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 (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) { /* No unread messages. */ + raw_spin_unlock(&syslog_lock); logbuf_unlock_irq(); return 0; } @@ -1744,6 +1771,7 @@ 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 */ @@ -2986,7 +3014,12 @@ 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