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 05BDDC433E0 for ; Tue, 30 Mar 2021 15:36:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D0F8B619D3 for ; Tue, 30 Mar 2021 15:36:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232418AbhC3PgG (ORCPT ); Tue, 30 Mar 2021 11:36:06 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:44856 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232443AbhC3Pf1 (ORCPT ); Tue, 30 Mar 2021 11:35:27 -0400 From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1617118516; 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=bPl+s+JpKl89Q4u3IDJDwNQFwzL5H5hBnoVBUHnRpbA=; b=1jb1cXqxbsBUQOZHYPAbpVa75YIMSO4/kd3m3n84w/GO91vOu8rMrdkEMy8yam+JMbn6av ZIgeG2grXn47RAJGkeDxVXbfclotdmooLWmT+q5aWcTFHPNxNNV01n/f9cktehDcLJmwN1 GVPzNY+cOrIO+pBPSSuMRXdnGFJUzrn7N8JwAIUpvkKlLKOGFdEQ+odkPD0KHdJyW1qN6m y6D9uyOpEkOvpKQHfe+g7RBw22nFs0N/ejHGi0PqH7/GCb60yM39yPQIYm5p2nztateO0l qpozV7taIgubMj5QnISOkhPyi4sAi3DOhD2J57hTTut7XPPWLjrHkAE0H0yWUQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1617118516; 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=bPl+s+JpKl89Q4u3IDJDwNQFwzL5H5hBnoVBUHnRpbA=; b=829kVO9RYfHlI7YMVeF02yY2iFoG8AO0WU6BSher+temKlOCNH0/evh9LIpxUegODsyKtG akqjfEKPlJtBrgAQ== To: Petr Mladek Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v2 4/5] printk: convert @syslog_lock to mutex Date: Tue, 30 Mar 2021 17:35:11 +0200 Message-Id: <20210330153512.1182-5-john.ogness@linutronix.de> In-Reply-To: <20210330153512.1182-1-john.ogness@linutronix.de> References: <20210330153512.1182-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org @syslog_lock was a raw_spin_lock to simplify the transition of removing @logbuf_lock and the safe buffers. With that transition complete, and since all uses of @syslog_lock are within sleepable contexts, @syslog_lock can become a mutex. Note that until now register_console() would disable interrupts using irqsave, which implies that it may be called with interrupts disabled. And indeed, there is one possible call chain on parisc where this happens: handle_interruption(code=1) /* High-priority machine check (HPMC) */ pdc_console_restart() pdc_console_init_force() register_console() However, register_console() calls console_lock(), which might sleep. So it has never been allowed to call register_console() from an atomic context and the above call chain is a bug. Signed-off-by: John Ogness --- Note: The removal of read_syslog_seq_irq() is technically a small step backwards. But the follow-up patch moves forward again and closes a window that existed with read_syslog_seq_irq() and @syslog_lock as a spin_lock. kernel/printk/printk.c | 49 +++++++++++++++++------------------------- 1 file changed, 20 insertions(+), 29 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index f090d6a1b39e..b771aae46445 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -356,7 +356,7 @@ enum log_flags { }; /* syslog_lock protects syslog_* variables and write access to clear_seq. */ -static DEFINE_RAW_SPINLOCK(syslog_lock); +static DEFINE_MUTEX(syslog_lock); #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); @@ -1497,9 +1497,9 @@ static int syslog_print(char __user *buf, int size) size_t n; size_t skip; - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); if (!prb_read_valid(prb, syslog_seq, &r)) { - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); break; } if (r.info->seq != syslog_seq) { @@ -1528,7 +1528,7 @@ static int syslog_print(char __user *buf, int size) syslog_partial += n; } else n = 0; - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); if (!n) break; @@ -1592,9 +1592,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear) } if (clear) { - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); latched_seq_write(&clear_seq, seq); - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); } kfree(text); @@ -1603,21 +1603,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear) static void syslog_clear(void) { - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); latched_seq_write(&clear_seq, prb_next_seq(prb)); - raw_spin_unlock_irq(&syslog_lock); -} - -/* 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; + mutex_unlock(&syslog_lock); } int do_syslog(int type, char __user *buf, int len, int source) @@ -1626,6 +1614,7 @@ 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) @@ -1644,8 +1633,12 @@ int do_syslog(int type, char __user *buf, int len, int source) if (!access_ok(buf, len)) return -EFAULT; - error = wait_event_interruptible(log_wait, - prb_read_valid(prb, read_syslog_seq_irq(), NULL)); + /* Get a consistent copy of @syslog_seq. */ + mutex_lock(&syslog_lock); + seq = syslog_seq; + mutex_unlock(&syslog_lock); + + error = wait_event_interruptible(log_wait, prb_read_valid(prb, seq, NULL)); if (error) return error; error = syslog_print(buf, len); @@ -1693,10 +1686,10 @@ int do_syslog(int type, char __user *buf, int len, int source) break; /* Number of chars in the log buffer */ case SYSLOG_ACTION_SIZE_UNREAD: - raw_spin_lock_irq(&syslog_lock); + mutex_lock(&syslog_lock); if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) { /* No unread messages. */ - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); return 0; } if (info.seq != syslog_seq) { @@ -1714,7 +1707,6 @@ int do_syslog(int type, char __user *buf, int len, int source) } else { bool time = syslog_partial ? syslog_time : printk_time; unsigned int line_count; - u64 seq; prb_for_each_info(syslog_seq, prb, seq, &info, &line_count) { @@ -1724,7 +1716,7 @@ int do_syslog(int type, char __user *buf, int len, int source) } error -= syslog_partial; } - raw_spin_unlock_irq(&syslog_lock); + mutex_unlock(&syslog_lock); break; /* Size of the log buffer */ case SYSLOG_ACTION_SIZE_BUFFER: @@ -2925,7 +2917,6 @@ static int try_enable_new_console(struct console *newcon, bool user_specified) */ void register_console(struct console *newcon) { - unsigned long flags; struct console *bcon = NULL; int err; @@ -3030,9 +3021,9 @@ void register_console(struct console *newcon) exclusive_console_stop_seq = console_seq; /* Get a consistent copy of @syslog_seq. */ - raw_spin_lock_irqsave(&syslog_lock, flags); + mutex_lock(&syslog_lock); console_seq = syslog_seq; - raw_spin_unlock_irqrestore(&syslog_lock, flags); + mutex_unlock(&syslog_lock); } console_unlock(); console_sysfs_notify(); -- 2.20.1