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: Anton Volkov <avolkov@ispras.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 15 deletions

diff --git a/drivers/isdn/hysdn/hysdn_proclog.c b/drivers/isdn/hysdn/hysdn_proclog.c
index 7b5fd8fb1761..aaca0b3d662e 100644
--- a/drivers/isdn/hysdn/hysdn_proclog.c
+++ b/drivers/isdn/hysdn/hysdn_proclog.c
@@ -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
-                                break;
-                }               /* pd->log_head->next */
-        pd->del_lock--;         /* release lock level */
+        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 {
+                        break;
+                }
+        }               /* pd->log_head->next */
+
+        spin_unlock_irqrestore(&card->hysdn_lock, flags);
+
         wake_up_interruptible(&(pd->rd_queue));         /* announce new entry */
 }                               /* put_log_buffer */