Commit 35b2b163 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: use atomic64_t for devkmsg_user.seq 



@user->seq is indirectly protected by @logbuf_lock. Once @logbuf_lock
is removed, @user->seq will be no longer safe from an atomicity point
of view.

In preparation for the removal of @logbuf_lock, change it to
atomic64_t to provide this safety.

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/20210303101528.29901-10-john.ogness@linutronix.de
parent 7d7a23a9

kernel/printk/printk.c

+12 −12
Original line number Diff line number Diff line
@@ -662,7 +662,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size, 


/* /dev/kmsg - userspace message inject/listen interface */

struct devkmsg_user {

	u64 seq;

	atomic64_t seq;

	struct ratelimit_state rs;

	struct mutex lock;

	char buf[CONSOLE_EXT_LOG_MAX];
@@ -763,7 +763,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
		return ret;



	logbuf_lock_irq();

	if (!prb_read_valid(prb, user->seq, r)) {

	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {

		if (file->f_flags & O_NONBLOCK) {

			ret = -EAGAIN;

			logbuf_unlock_irq();
@@ -772,15 +772,15 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 


		logbuf_unlock_irq();

		ret = wait_event_interruptible(log_wait,

					prb_read_valid(prb, user->seq, r));

				prb_read_valid(prb, atomic64_read(&user->seq), r));

		if (ret)

			goto out;

		logbuf_lock_irq();

	}



	if (r->info->seq != user->seq) {

	if (r->info->seq != atomic64_read(&user->seq)) {

		/* our last seen message is gone, return error and reset */

		user->seq = r->info->seq;

		atomic64_set(&user->seq, r->info->seq);

		ret = -EPIPE;

		logbuf_unlock_irq();

		goto out;
@@ -791,7 +791,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
				  &r->text_buf[0], r->info->text_len,

				  &r->info->dev_info);



	user->seq = r->info->seq + 1;

	atomic64_set(&user->seq, r->info->seq + 1);

	logbuf_unlock_irq();



	if (len > count) {
@@ -831,7 +831,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) 
	switch (whence) {

	case SEEK_SET:

		/* the first record */

		user->seq = prb_first_valid_seq(prb);

		atomic64_set(&user->seq, prb_first_valid_seq(prb));

		break;

	case SEEK_DATA:

		/*
@@ -839,11 +839,11 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) 
		 * like issued by 'dmesg -c'. Reading /dev/kmsg itself

		 * changes no global state, and does not clear anything.

		 */

		user->seq = latched_seq_read_nolock(&clear_seq);

		atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));

		break;

	case SEEK_END:

		/* after the last record */

		user->seq = prb_next_seq(prb);

		atomic64_set(&user->seq, prb_next_seq(prb));

		break;

	default:

		ret = -EINVAL;
@@ -864,9 +864,9 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait) 
	poll_wait(file, &log_wait, wait);



	logbuf_lock_irq();

	if (prb_read_valid_info(prb, user->seq, &info, NULL)) {

	if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {

		/* return error when data has vanished underneath us */

		if (info.seq != user->seq)

		if (info.seq != atomic64_read(&user->seq))

			ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;

		else

			ret = EPOLLIN|EPOLLRDNORM;
@@ -905,7 +905,7 @@ static int devkmsg_open(struct inode *inode, struct file *file) 
			&user->text_buf[0], sizeof(user->text_buf));



	logbuf_lock_irq();

	user->seq = prb_first_valid_seq(prb);

	atomic64_set(&user->seq, prb_first_valid_seq(prb));

	logbuf_unlock_irq();



	file->private_data = user;