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From 5521ed0e06ffc572d9f0ebf5421ab23288899804 Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Thu, 10 Dec 2020 16:58:02 +0106
Subject: [PATCH 089/323] printk: add syslog_lock
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
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 <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
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 a351ed400c04..986fc9fad210 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -392,8 +392,12 @@ 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;
@@ -412,7 +416,7 @@ 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),
@@ -472,7 +476,7 @@ 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);
@@ -1532,7 +1536,9 @@ 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;
}
@@ -1562,6 +1568,7 @@ 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)
@@ -1628,8 +1635,11 @@ 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);
@@ -1639,10 +1649,24 @@ 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;
@@ -1666,8 +1690,9 @@ 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);
@@ -1716,8 +1741,10 @@ 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;
}
@@ -1746,6 +1773,7 @@ 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 */
@@ -2995,7 +3023,12 @@ 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();
--
2.43.0
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