Commit 5c53d819 authored by liu chuansheng's avatar liu chuansheng Committed by Greg Kroah-Hartman
Browse files

printk: replacing the raw_spin_lock/unlock with raw_spin_lock/unlock_irq 



In function devkmsg_read/writev/llseek/poll/open()..., the function
raw_spin_lock/unlock is used, there is potential deadlock case happening.
CPU1: thread1 doing the cat /dev/kmsg:
        raw_spin_lock(&logbuf_lock);
        while (user->seq == log_next_seq) {
when thread1 run here, at this time one interrupt is coming on CPU1 and running
based on this thread,if the interrupt handle called the printk which need the
logbuf_lock spin also, it will cause deadlock.

So we should use raw_spin_lock/unlock_irq here.

Acked-by: default avatarKay Sievers <kay@vrfy.org>
Signed-off-by: default avatarliu chuansheng <chuansheng.liu@intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 6887a413

kernel/printk.c

+12 −12
Original line number Diff line number Diff line
@@ -430,20 +430,20 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
	ret = mutex_lock_interruptible(&user->lock);

	if (ret)

		return ret;

	raw_spin_lock(&logbuf_lock);

	raw_spin_lock_irq(&logbuf_lock);

	while (user->seq == log_next_seq) {

		if (file->f_flags & O_NONBLOCK) {

			ret = -EAGAIN;

			raw_spin_unlock(&logbuf_lock);

			raw_spin_unlock_irq(&logbuf_lock);

			goto out;

		}



		raw_spin_unlock(&logbuf_lock);

		raw_spin_unlock_irq(&logbuf_lock);

		ret = wait_event_interruptible(log_wait,

					       user->seq != log_next_seq);

		if (ret)

			goto out;

		raw_spin_lock(&logbuf_lock);

		raw_spin_lock_irq(&logbuf_lock);

	}



	if (user->seq < log_first_seq) {
@@ -451,7 +451,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
		user->idx = log_first_idx;

		user->seq = log_first_seq;

		ret = -EPIPE;

		raw_spin_unlock(&logbuf_lock);

		raw_spin_unlock_irq(&logbuf_lock);

		goto out;

	}
@@ -501,7 +501,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 


	user->idx = log_next(user->idx);

	user->seq++;

	raw_spin_unlock(&logbuf_lock);

	raw_spin_unlock_irq(&logbuf_lock);



	if (len > count) {

		ret = -EINVAL;
@@ -528,7 +528,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) 
	if (offset)

		return -ESPIPE;



	raw_spin_lock(&logbuf_lock);

	raw_spin_lock_irq(&logbuf_lock);

	switch (whence) {

	case SEEK_SET:

		/* the first record */
@@ -552,7 +552,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence) 
	default:

		ret = -EINVAL;

	}

	raw_spin_unlock(&logbuf_lock);

	raw_spin_unlock_irq(&logbuf_lock);

	return ret;

}
@@ -566,14 +566,14 @@ static unsigned int devkmsg_poll(struct file *file, poll_table *wait) 


	poll_wait(file, &log_wait, wait);



	raw_spin_lock(&logbuf_lock);

	raw_spin_lock_irq(&logbuf_lock);

	if (user->seq < log_next_seq) {

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

		if (user->seq < log_first_seq)

			ret = POLLIN|POLLRDNORM|POLLERR|POLLPRI;

		ret = POLLIN|POLLRDNORM;

	}

	raw_spin_unlock(&logbuf_lock);

	raw_spin_unlock_irq(&logbuf_lock);



	return ret;

}
@@ -597,10 +597,10 @@ static int devkmsg_open(struct inode *inode, struct file *file) 


	mutex_init(&user->lock);



	raw_spin_lock(&logbuf_lock);

	raw_spin_lock_irq(&logbuf_lock);

	user->idx = log_first_idx;

	user->seq = log_first_seq;

	raw_spin_unlock(&logbuf_lock);

	raw_spin_unlock_irq(&logbuf_lock);



	file->private_data = user;

	return 0;

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