Re: [PATCH bpf 3/3] selftests/bpf: Test freeing sockmap/sockhash with a socket in it

[Jakub Sitnicki <jakub@cloudflare.com>]

On Mon, Feb 10, 2020 at 03:55 AM GMT, John Fastabend wrote:
> Jakub Sitnicki wrote:
>> On Sun, Feb 09, 2020 at 03:41 AM CET, Alexei Starovoitov wrote:
>> > On Thu, Feb 6, 2020 at 3:28 AM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>> >>
>> >> Commit 7e81a3530206 ("bpf: Sockmap, ensure sock lock held during tear
>> >> down") introduced sleeping issues inside RCU critical sections and while
>> >> holding a spinlock on sockmap/sockhash tear-down. There has to be at least
>> >> one socket in the map for the problem to surface.
>> >>
>> >> This adds a test that triggers the warnings for broken locking rules. Not a
>> >> fix per se, but rather tooling to verify the accompanying fixes. Run on a
>> >> VM with 1 vCPU to reproduce the warnings.
>> >>
>> >> Fixes: 7e81a3530206 ("bpf: Sockmap, ensure sock lock held during tear down")
>> >> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
>> >
>> > selftests/bpf no longer builds for me.
>> > make
>> >   BINARY   test_maps
>> >   TEST-OBJ [test_progs] sockmap_basic.test.o
>> > /data/users/ast/net/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c:
>> > In function ‘connected_socket_v4’:
>> > /data/users/ast/net/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c:20:11:
>> > error: ‘TCP_REPAIR_ON’ undeclared (first use in this function); did
>> > you mean ‘TCP_REPAIR’?
>> >    20 |  repair = TCP_REPAIR_ON;
>> >       |           ^~~~~~~~~~~~~
>> >       |           TCP_REPAIR
>> > /data/users/ast/net/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c:20:11:
>> > note: each undeclared identifier is reported only once for each
>> > function it appears in
>> > /data/users/ast/net/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c:29:11:
>> > error: ‘TCP_REPAIR_OFF_NO_WP’ undeclared (first use in this function);
>> > did you mean ‘TCP_REPAIR_OPTIONS’?
>> >    29 |  repair = TCP_REPAIR_OFF_NO_WP;
>> >       |           ^~~~~~~~~~~~~~~~~~~~
>> >       |           TCP_REPAIR_OPTIONS
>> >
>> > Clearly /usr/include/linux/tcp.h is too old.
>> > Suggestions?
>>
>> Sorry for the inconvenience. I see that tcp.h header is missing under
>> linux/tools/include/uapi/.
>
> How about we just add the couple defines needed to sockmap_basic.c I don't
> see a need to pull in all of tcp.h just for a couple defines that wont
> change anyways.

Looking back at how this happened. test_progs.h pulls in netinet/tcp.h:

# 19 "/home/jkbs/src/linux/tools/testing/selftests/bpf/test_progs.h" 2
# 1 "/usr/include/netinet/tcp.h" 1 3 4
# 92 "/usr/include/netinet/tcp.h" 3 4

A glibc header, which gained TCP_REPAIR_* constants in 2.29 [0]:

$ git describe --contains 5cd7dbdea13eb302620491ef44837b17e9d39c5a
glibc-2.29~510

Pulling in linux/tcp.h would conflict with struct definitions in
netinet/tcp.h. So redefining the possibly missing constants, like John
suggests, is the right way out.

I'm not sure, though, how to protect against such mistakes in the
future. Any ideas?

[0] https://sourceware.org/git/?p=glibc.git;a=commit;h=5cd7dbdea13eb302620491ef44837b17e9d39c5a

>
>>
>> I have been building against my distro kernel headers, completely
>> unaware of this. This is an oversight on my side.
>>
>> Can I ask for a revert? I'm traveling today with limited ability to
>> post patches.
>
> I don't think we need a full revert.
>
>>
>> I can resubmit the test with the missing header for bpf-next once it
>> reopens.
>
> If you are traveling I'll post a patch with the defines.

Thanks, again.