On Tue, 28 Feb 2023 12:23:46 +0100 Eric Dumazet wrote:

This report mentions sendpage, but sendmsg() would have the same issue.

A thread might be blocked in sk_stream_wait_memory() with the mutex
held, for an arbitrary amount of time,
say if the remote peer stays in RWIN 0 for hours.

This prevents tx_work from making progress, and
tls_sw_cancel_work_tx() would be stuck forever.

The consensus is that the kernel shouts a warning if a thread has been
waiting on a mutex
more than 120 seconds (check_hung_uninterruptible_tasks())

Thanks for explaining, let's see if I can hack a fix together..