Commit 636babdc authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: add syslog_lock 



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: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210303101528.29901-11-john.ogness@linutronix.de
parent 35b2b163

kernel/printk/printk.c

+37 −4
Original line number Diff line number Diff line
@@ -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);
@@ -1529,7 +1533,9 @@ 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;

		}
@@ -1559,6 +1565,7 @@ 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)
@@ -1625,8 +1632,11 @@ 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);
@@ -1636,10 +1646,24 @@ 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;
@@ -1663,8 +1687,9 @@ 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);
@@ -1713,8 +1738,10 @@ 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;

		}
@@ -1743,6 +1770,7 @@ 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 */
@@ -2992,7 +3020,12 @@ 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();