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Subject[PATCH net] hv_sock: Fix hang when a connection is closed
Date

hvs_do_close_lock_held() may decrease the reference count to 0 and free the
sk struct completely, and then the following release_sock(sk) may hang.

Fixes: a9eeb998c28d ("hv_sock: Add support for delayed close")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: stable@vger.kernel.org

---
With the proper kernel debugging options enabled, first a warning can
appear:

kworker/1:0/4467 is freeing memory ..., with a lock still held there!
stack backtrace:
Workqueue: events vmbus_onmessage_work [hv_vmbus]
Call Trace:
dump_stack+0x67/0x90
debug_check_no_locks_freed.cold.52+0x78/0x7d
slab_free_freelist_hook+0x85/0x140
kmem_cache_free+0xa5/0x380
__sk_destruct+0x150/0x260
hvs_close_connection+0x24/0x30 [hv_sock]
vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
process_one_work+0x241/0x600
worker_thread+0x3c/0x390
kthread+0x11b/0x140
ret_from_fork+0x24/0x30

and then the following release_sock(sk) can hang:

watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/1:0:4467]
...
irq event stamp: 62890
CPU: 1 PID: 4467 Comm: kworker/1:0 Tainted: G W 5.2.0+ #39
Workqueue: events vmbus_onmessage_work [hv_vmbus]
RIP: 0010:queued_spin_lock_slowpath+0x2b/0x1e0
...
Call Trace:
do_raw_spin_lock+0xab/0xb0
release_sock+0x19/0xb0
vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
process_one_work+0x241/0x600
worker_thread+0x3c/0x390
kthread+0x11b/0x140
ret_from_fork+0x24/0x30

net/vmw_vsock/hyperv_transport.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index f2084e3f7aa4..efbda8ef1eff 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c
@@ -309,9 +309,16 @@ static void hvs_close_connection(struct vmbus_channel *chan)
{
struct sock *sk = get_per_channel_state(chan);

+ /* Grab an extra reference since hvs_do_close_lock_held() may decrease
+ * the reference count to 0 by calling sock_put(sk).
+ */
+ sock_hold(sk);
+
lock_sock(sk);
hvs_do_close_lock_held(vsock_sk(sk), true);
release_sock(sk);
+
+ sock_put(sk);
}

static void hvs_open_connection(struct vmbus_channel *chan)
--
2.19.1
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