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>

diff --git a/drivers/isdn/hysdn/hysdn_proclog.c b/drivers/isdn/hysdn/hysdn_proclog.c
index 7b5fd8fb1761d1912be615ee14571e420dc4c92b..aaca0b3d662eb18bda0848652c309985d5f6ad0e 100644 (file)
--- 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 */