2020-06-12 09:11:49

by Wang Hai

Subject: [PATCH v2] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

p9_read_work and p9_fd_cancelled may be called concurrently.
In some cases, req->req_list may be deleted by both p9_read_work
and p9_fd_cancelled.

We can fix it by ignoring replies associated with a cancelled
request and ignoring cancelled request if message has been received
before lock.

Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
Reported-by: [email protected]
Signed-off-by: Wang Hai <[email protected]>
---
v1->v2:
1. Add ignoring replies associated with a cancelled request.
2. Improved some descriptions suggested by Dominique.
net/9p/trans_fd.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index 13cd683a658a..3f67803123be 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -362,6 +362,10 @@ static void p9_read_work(struct work_struct *work)
if (m->rreq->status == REQ_STATUS_SENT) {
list_del(&m->rreq->req_list);
p9_client_cb(m->client, m->rreq, REQ_STATUS_RCVD);
+ } else if (m->rreq->status == REQ_STATUS_FLSHD) {
+ /* Ignore replies associated with a cancelled request. */
+ p9_debug(P9_DEBUG_TRANS,
+ "Ignore replies associated with a cancelled request\n");
} else {
spin_unlock(&m->client->lock);
p9_debug(P9_DEBUG_ERROR,
@@ -703,11 +707,20 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
{
p9_debug(P9_DEBUG_TRANS, "client %p req %p\n", client, req);

+ spin_lock(&client->lock);
+ /* Ignore cancelled request if message has been received
+ * before lock.
+ */
+ if (req->status == REQ_STATUS_RCVD) {
+ spin_unlock(&client->lock);
+ return 0;
+ }
+
/* we haven't received a response for oldreq,
* remove it from the list.
*/
- spin_lock(&client->lock);
list_del(&req->req_list);
+ req->status = REQ_STATUS_FLSHD;
spin_unlock(&client->lock);
p9_req_put(req);

--
2.17.1

2020-06-12 09:15:29

by Dominique Martinet

Subject: Re: [PATCH v2] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

Wang Hai wrote on Fri, Jun 12, 2020:
> p9_read_work and p9_fd_cancelled may be called concurrently.
> In some cases, req->req_list may be deleted by both p9_read_work
> and p9_fd_cancelled.
>
> We can fix it by ignoring replies associated with a cancelled
> request and ignoring cancelled request if message has been received
> before lock.
>
> Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
> Reported-by: [email protected]
> Signed-off-by: Wang Hai <[email protected]>

Thanks! looks good to me, I'll queue for 5.9 as well unless you're in a
hurry.
--
Dominique

2020-06-12 09:27:02

by Wang Hai

Subject: Re: [PATCH v2] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

在 2020/6/12 17:10, Dominique Martinet 写道:
> Wang Hai wrote on Fri, Jun 12, 2020:
>> p9_read_work and p9_fd_cancelled may be called concurrently.
>> In some cases, req->req_list may be deleted by both p9_read_work
>> and p9_fd_cancelled.
>>
>> We can fix it by ignoring replies associated with a cancelled
>> request and ignoring cancelled request if message has been received
>> before lock.
>>
>> Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
>> Reported-by: [email protected]
>> Signed-off-by: Wang Hai <[email protected]>
> Thanks! looks good to me, I'll queue for 5.9 as well unless you're in a
> hurry.
Ok, thanks.