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SubjectRe: [PATCH] libceph: protect pending flags in ceph_con_keepalive()
On Thu, Jan 3, 2019 at 4:50 AM Myungho Jung <mhjungk@gmail.com> wrote:
> I reproduced on vm using syzkaller utils and verified the fix by syzbot.

Hi Myungho,

I think this might be a better fix:

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index d5718284db57..c5f5313e3537 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -3205,10 +3205,11 @@ void ceph_con_keepalive(struct ceph_connection *con)
{
dout("con_keepalive %p\n", con);
mutex_lock(&con->mutex);
+ con_flag_set(con, CON_FLAG_KEEPALIVE_PENDING);
clear_standby(con);
mutex_unlock(&con->mutex);
- if (con_flag_test_and_set(con, CON_FLAG_KEEPALIVE_PENDING) == 0 &&
- con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
+
+ if (con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
queue_con(con);
}
EXPORT_SYMBOL(ceph_con_keepalive);
WRITE_PENDING can be set without con->mutex held from socket callbacks.
This is the reason we use atomic bit ops here, so testing WRITE_PENDING
under the lock didn't make sense to me.

At the same time, KEEPALIVE_PENDING could have been a non-atomic flag.
I spent some time trying to make sense of conditioning queue_con() call
on the previous value of KEEPALIVE_PENDING and couldn't see any, so I'm
setting it with con_flag_set(), making ceph_con_keepalive() symmetric
with ceph_con_send().

Thanks,

Ilya

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