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From: John Ogness <john.ogness@linutronix.de>
Date: Thu, 10 Dec 2020 16:58:02 +0106
Subject: [PATCH 05/21] printk: add syslog_lock
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.8-rt24.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 with need their
own synchronization method. Introduce @syslog_lock for this
purpose.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk.c | 32 +++++++++++++++++++++++++++++---
1 file changed, 29 insertions(+), 3 deletions(-)
--- 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_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;
@@ -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. */
void latched_seq_write(struct latched_seq *ls, u64 val)
{
raw_write_seqcount_latch(&ls->latch);
@@ -1462,7 +1466,9 @@ static int syslog_print(char __user *buf
size_t skip;
logbuf_lock_irq();
+ spin_lock(&syslog_lock);
if (!prb_read_valid(prb, syslog_seq, &r)) {
+ spin_unlock(&syslog_lock);
logbuf_unlock_irq();
break;
}
@@ -1492,6 +1498,7 @@ static int syslog_print(char __user *buf
syslog_partial += n;
} else
n = 0;
+ spin_unlock(&syslog_lock);
logbuf_unlock_irq();
if (!n)
@@ -1569,8 +1576,11 @@ static int syslog_print_all(char __user
break;
}
- if (clear)
+ if (clear) {
+ spin_lock(&syslog_lock);
latched_seq_write(&clear_seq, seq);
+ spin_unlock(&syslog_lock);
+ }
logbuf_unlock_irq();
kfree(text);
@@ -1580,7 +1590,9 @@ static int syslog_print_all(char __user
static void syslog_clear(void)
{
logbuf_lock_irq();
+ spin_lock(&syslog_lock);
latched_seq_write(&clear_seq, prb_next_seq(prb));
+ spin_unlock(&syslog_lock);
logbuf_unlock_irq();
}
@@ -1589,6 +1601,7 @@ int do_syslog(int type, char __user *buf
bool clear = false;
static int saved_console_loglevel = LOGLEVEL_DEFAULT;
int error;
+ u64 seq;
error = check_syslog_permissions(type, source);
if (error)
@@ -1606,8 +1619,14 @@ int do_syslog(int type, char __user *buf
return 0;
if (!access_ok(buf, len))
return -EFAULT;
+
+ /* Get a consistent copy of @syslog_seq. */
+ spin_lock_irq(&syslog_lock);
+ seq = syslog_seq;
+ 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);
@@ -1656,6 +1675,7 @@ int do_syslog(int type, char __user *buf
/* Number of chars in the log buffer */
case SYSLOG_ACTION_SIZE_UNREAD:
logbuf_lock_irq();
+ 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);
@@ -1682,6 +1702,7 @@ int do_syslog(int type, char __user *buf
}
error -= syslog_partial;
}
+ spin_unlock(&syslog_lock);
logbuf_unlock_irq();
break;
/* Size of the log buffer */
@@ -2925,7 +2946,12 @@ void register_console(struct console *ne
*/
exclusive_console = newcon;
exclusive_console_stop_seq = console_seq;
+
+ /* Get a consistent copy of @syslog_seq. */
+ spin_lock(&syslog_lock);
console_seq = syslog_seq;
+ spin_unlock(&syslog_lock);
+
logbuf_unlock_irqrestore(flags);
}
console_unlock();
|
