Re: [PATCH net 2/2] selftests: net: add a test for closing a netlink socket ith dump in progress

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Jakub Kicinski <kuba@kernel.org>
Date: Mon,  4 Nov 2024 17:03:47 -0800
> Close a socket with dump in progress. We need a dump which generates
> enough info not to fit into a single skb. Policy dump fits the bill.
> 
> Use the trick discovered by syzbot for keeping a ref on the socket
> longer than just close, with mqueue.
> 
>   TAP version 13
>   1..3
>   # Starting 3 tests from 1 test cases.
>   #  RUN           global.test_sanity ...
>   #            OK  global.test_sanity
>   ok 1 global.test_sanity
>   #  RUN           global.close_in_progress ...
>   #            OK  global.close_in_progress
>   ok 2 global.close_in_progress
>   #  RUN           global.close_with_ref ...
>   #            OK  global.close_with_ref
>   ok 3 global.close_with_ref
>   # PASSED: 3 / 3 tests passed.
>   # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> Note that this test is not expected to fail but rather crash
> the kernel if we get the cleanup wrong.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

TIL mq_notify, and the trick was interesting that calls fdget(),
netlink_getsockbyfilp(), and fdput() to keep sock_hold() only :)