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Subject[PATCH v2] hysdn: fix to a race condition in put_log_buffer
Date
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>
---
v2: Fixed coding style issues

drivers/isdn/hysdn/hysdn_proclog.c | 28 +++++++++++++---------------
1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/drivers/isdn/hysdn/hysdn_proclog.c b/drivers/isdn/hysdn/hysdn_proclog.c
index 7b5fd8f..aaca0b3 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 */

--
2.7.4
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