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Commit b925ef37 authored by Anton Volkov's avatar Anton Volkov Committed by David S. Miller
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hysdn: fix to a race condition in put_log_buffer 



The synchronization type that was used earlier to guard the loop that
deletes unused log buffers may lead to a situation that prevents any
thread from going through the loop.

The patch deletes previously used synchronization mechanism and moves
the loop under the spin_lock so the similar cases won't be feasible in
the future.

Found by by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: default avatarAnton Volkov <avolkov@ispras.ru>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ec2c6726

drivers/isdn/hysdn/hysdn_proclog.c

+13 −15
Original line number Diff line number Diff line
@@ -44,7 +44,6 @@ struct procdata { 
	char log_name[15];	/* log filename */

	struct log_data *log_head, *log_tail;	/* head and tail for queue */

	int if_used;		/* open count for interface */

	int volatile del_lock;	/* lock for delete operations */

	unsigned char logtmp[LOG_MAX_LINELEN];

	wait_queue_head_t rd_queue;

};
@@ -102,7 +101,6 @@ put_log_buffer(hysdn_card *card, char *cp) 
{

	struct log_data *ib;

	struct procdata *pd = card->proclog;

	int i;

	unsigned long flags;



	if (!pd)
@@ -126,21 +124,21 @@ put_log_buffer(hysdn_card *card, char *cp) 
	else

		pd->log_tail->next = ib;	/* follows existing messages */

	pd->log_tail = ib;	/* new tail */

	i = pd->del_lock++;	/* get lock state */

	spin_unlock_irqrestore(&card->hysdn_lock, flags);



	/* delete old entrys */

	if (!i)

	while (pd->log_head->next) {

		if ((pd->log_head->usage_cnt <= 0) &&

		    (pd->log_head->next->usage_cnt <= 0)) {

			ib = pd->log_head;

			pd->log_head = pd->log_head->next;

			kfree(ib);

			} else

		} else {

			break;

		}

	}		/* pd->log_head->next */

	pd->del_lock--;		/* release lock level */



	spin_unlock_irqrestore(&card->hysdn_lock, flags);



	wake_up_interruptible(&(pd->rd_queue));		/* announce new entry */

}				/* put_log_buffer */