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9p-trans_fd: fix trans_fd::p9_conn_destroy() 

p9_conn_destroy() first kills all current requests by calling
p9_conn_cancel(), then waits for the request list to be cleared by
waiting on p9_conn->equeue.  After that, polling is stopped and the
trans is destroyed.  This sequence has a few problems.

* Read and write works were never cancelled and the p9_conn can be
  destroyed while the works are running as r/w works remove requests
  from the list and dereference the p9_conn from them.

* The list emptiness wait using p9_conn->equeue wouldn't trigger
  because p9_conn_cancel() always clears all the lists and the only
  way the wait can be triggered is to have another task to issue a
  request between the slim window between p9_conn_cancel() and the
  wait, which isn't safe under the current implementation with or
  without the wait.

This patch fixes the problem by first stopping poll, which can
schedule r/w works, first and cancle r/w works which guarantees that
r/w works are not and will not run from that point and then calling
p9_conn_cancel() and do the rest of destruction.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
This commit is contained in:
Tejun Heo 2008-09-24 16:22:23 -05:00 committed by Eric Van Hensbergen
parent 72029fe85d
commit 7dc5d24be0
1 changed files with 5 additions and 19 deletions
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24
net/9p/trans_fd.c
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@ -151,7 +151,6 @@ struct p9_mux_poll_task {
* @trans: reference to transport instance for this connection
* @tagpool: id accounting for transactions
* @err: error state
* @equeue: event wait_q (?)
* @req_list: accounting for requests which have been sent
* @unsent_req_list: accounting for requests that haven't been sent
* @rcall: current response &p9_fcall structure
@ -178,7 +177,6 @@ struct p9_conn {
struct p9_trans *trans;
struct p9_idpool *tagpool;
int err;
wait_queue_head_t equeue;
struct list_head req_list;
struct list_head unsent_req_list;
struct p9_fcall *rcall;
@ -430,7 +428,6 @@ static struct p9_conn *p9_conn_create(struct p9_trans *trans)
}
m->err = 0;
init_waitqueue_head(&m->equeue);
INIT_LIST_HEAD(&m->req_list);
INIT_LIST_HEAD(&m->unsent_req_list);
m->rcall = NULL;
@ -483,18 +480,13 @@ static void p9_conn_destroy(struct p9_conn *m)
{
P9_DPRINTK(P9_DEBUG_MUX, "mux %p prev %p next %p\n", m,
m->mux_list.prev, m->mux_list.next);
p9_conn_cancel(m, -ECONNRESET);
if (!list_empty(&m->req_list)) {
/* wait until all processes waiting on this session exit */
P9_DPRINTK(P9_DEBUG_MUX,
"mux %p waiting for empty request queue\n", m);
wait_event_timeout(m->equeue, (list_empty(&m->req_list)), 5000);
P9_DPRINTK(P9_DEBUG_MUX, "mux %p request queue empty: %d\n", m,
list_empty(&m->req_list));
}
p9_mux_poll_stop(m);
cancel_work_sync(&m->rq);
cancel_work_sync(&m->wq);
p9_conn_cancel(m, -ECONNRESET);
m->trans = NULL;
p9_idpool_destroy(m->tagpool);
kfree(m);
@ -840,8 +832,6 @@ static void p9_read_work(struct work_struct *work)
(*req->cb) (req, req->cba);
else
kfree(req->rcall);
wake_up(&m->equeue);
}
} else {
if (err >= 0 && rcall->id != P9_RFLUSH)
@ -984,8 +974,6 @@ static void p9_mux_flush_cb(struct p9_req *freq, void *a)
(*req->cb) (req, req->cba);
else
kfree(req->rcall);
wake_up(&m->equeue);
}
kfree(freq->tcall);
@ -1191,8 +1179,6 @@ void p9_conn_cancel(struct p9_conn *m, int err)
else
kfree(req->rcall);
}
wake_up(&m->equeue);
}
/**