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hysdn: fix to a race condition in put_log_buffer

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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>
This commit is contained in:
Anton Volkov 2017-08-07 15:54:14 +03:00 • committed by David S. Miller
parent ec2c672632
commit b925ef37b0
1 changed files with 13 additions and 15 deletions
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28
drivers/isdn/hysdn/hysdn_proclog.c
View file

@ -44,7 +44,6 @@ struct procdata {
char log_name[15]; /* log filename */ char log_name[15]; /* log filename */
struct log_data *log_head, *log_tail; /* head and tail for queue */ struct log_data *log_head, *log_tail; /* head and tail for queue */
int if_used; /* open count for interface */ int if_used; /* open count for interface */
int volatile del_lock; /* lock for delete operations */
unsigned char logtmp[LOG_MAX_LINELEN]; unsigned char logtmp[LOG_MAX_LINELEN];
wait_queue_head_t rd_queue; wait_queue_head_t rd_queue;
}; };
@ -102,7 +101,6 @@ put_log_buffer(hysdn_card *card, char *cp)
{ {
struct log_data *ib; struct log_data *ib;
struct procdata *pd = card->proclog; struct procdata *pd = card->proclog;
int i;
unsigned long flags; unsigned long flags;
if (!pd) if (!pd)
@ -126,21 +124,21 @@ put_log_buffer(hysdn_card *card, char *cp)
else else
pd->log_tail->next = ib; /* follows existing messages */ pd->log_tail->next = ib; /* follows existing messages */
pd->log_tail = ib; /* new tail */ pd->log_tail = ib; /* new tail */
i = pd->del_lock++; /* get lock state */
spin_unlock_irqrestore(&card->hysdn_lock, flags);
/* delete old entrys */ /* delete old entrys */
if (!i) while (pd->log_head->next) {
while (pd->log_head->next) { if ((pd->log_head->usage_cnt <= 0) &&
if ((pd->log_head->usage_cnt <= 0) && (pd->log_head->next->usage_cnt <= 0)) {
(pd->log_head->next->usage_cnt <= 0)) { ib = pd->log_head;
ib = pd->log_head; pd->log_head = pd->log_head->next;
pd->log_head = pd->log_head->next; kfree(ib);
kfree(ib); } else {
} else break;
break; }
} /* pd->log_head->next */ } /* 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 */ wake_up_interruptible(&(pd->rd_queue)); /* announce new entry */
} /* put_log_buffer */ } /* put_log_buffer */