Current main event loop (event_loop()) of tgtd has a possibility of
segmentation fault. The problem is caused by the below sequence:
1. Event A, B are ready so epoll_wait(2) returns.
2. The handler of the event A is called. In the event handler, the
event B is deleted with tgt_event_del()
3. event_loop() tries to call the handler of the event B. It causes
segfault because the event struct is already removed and freed.
For avoid this problem, this patch adds a new global variable
event_need_refresh. If the value of this variable is 1, event_loop()
calls epoll_wait(2) again for refreshing ready fd list. This patch
also lets tgt_event_del() to turn on the flag in its tail.
For example, we can produce segfault of tgtd under heavy load. Below
is a backtrace obtained from the core file:
(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x0000000000411419 in event_loop () at tgtd.c:414
#2 0x0000000000411b65 in main (argc=<value optimized out>, argv=<value optimized out>) at tgtd.c:591
To be honest, I still don't find an event handler which calls
tgt_event_del() for other fds. But with this modification, the above
segfault is avoided. The change seems to be effective.
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@xxxxxxxxxxxxx>
---
v3:
- update commit log for backtrace
- remove needless extern declaration in tgtd.h
v2: use the existing label "retry" instead of adding a new label
usr/tgtd.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/usr/tgtd.c b/usr/tgtd.c
index 50e1c83..04b31dc 100644
--- a/usr/tgtd.c
+++ b/usr/tgtd.c
@@ -212,6 +212,8 @@ static struct event_data *tgt_event_lookup(int fd)
return NULL;
}
+int event_need_refresh;
+
void tgt_event_del(int fd)
{
struct event_data *tev;
@@ -229,6 +231,8 @@ void tgt_event_del(int fd)
list_del(&tev->e_list);
free(tev);
+
+ event_need_refresh = 1;
}
int tgt_event_modify(int fd, int events)
@@ -426,6 +430,11 @@ retry:
for (i = 0; i < nevent; i++) {
tev = (struct event_data *) events[i].data.ptr;
tev->handler(tev->fd, events[i].events, tev->data);
+
+ if (event_need_refresh) {
+ event_need_refresh = 0;
+ goto retry;
+ }
}
}
--
1.7.10.4
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