From: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
To: stgt@vger.kernel.org
Cc: mitake.hitoshi@gmail.com, Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Subject: [PATCH v2] tgtd: refresh ready fds of event loop after event deletion
Date: Wed, 19 Feb 2014 13:21:59 +0900 [thread overview]
Message-ID: <1392783719-8868-1-git-send-email-mitake.hitoshi@lab.ntt.co.jp> (raw)
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
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@lab.ntt.co.jp>
---
usr/tgtd.c | 9 +++++++++
usr/tgtd.h | 2 ++
2 files changed, 11 insertions(+)
v2: use the existing label "retry" instead of adding a new label
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;
+ }
}
}
diff --git a/usr/tgtd.h b/usr/tgtd.h
index 8a25521..46b02af 100644
--- a/usr/tgtd.h
+++ b/usr/tgtd.h
@@ -405,4 +405,6 @@ struct service_action *
find_service_action(struct service_action *service_action,
uint32_t action);
+extern int event_need_refresh;
+
#endif
--
1.7.10.4
next reply other threads:[~2014-02-19 4:21 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-19 4:21 Hitoshi Mitake [this message]
2014-02-19 4:23 ` [PATCH v2] tgtd: refresh ready fds of event loop after event deletion Hitoshi Mitake
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