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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id u6-20020a05600c138600b0040d5a9d6b68sm2147371wmf.6.2024.01.10.04.49.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jan 2024 04:49:21 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 10 Jan 2024 13:49:19 +0100 To: Artem Savkov Cc: Yonghong Song , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next] selftests/bpf: fix potential premature unload in bpf_testmod Message-ID: References: <20240109164317.16371-1-asavkov@redhat.com> <82f55c0e-0ec8-4fe1-8d8c-b1de07558ad9@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jan 10, 2024 at 09:14:51AM +0100, Artem Savkov wrote: > On Tue, Jan 09, 2024 at 11:40:38AM -0800, Yonghong Song wrote: > > > > On 1/9/24 8:43 AM, Artem Savkov wrote: > > > It is possible for bpf_kfunc_call_test_release() to be called from > > > bpf_map_free_deferred() when bpf_testmod is already unloaded and > > > perf_test_stuct.cnt which it tries to decrease is no longer in memory. > > > This patch tries to fix the issue by waiting for all references to be > > > dropped in bpf_testmod_exit(). > > > > > > The issue can be triggered by running 'test_progs -t map_kptr' in 6.5, > > > but is obscured in 6.6 by d119357d07435 ("rcu-tasks: Treat only > > > synchronous grace periods urgently"). > > > > > > Fixes: 65eb006d85a2a ("bpf: Move kernel test kfuncs to bpf_testmod") > > > > Please add your Signed-off-by tag. > > Thanks for noticing. Will resend with signed-off-by and your ack. > > > I think the root cause is that bpf_kfunc_call_test_acquire() kfunc > > is defined in bpf_testmod and the kfunc returns some data in bpf_testmod. > > But the release function bpf_kfunc_call_test_release() is in the kernel. > > The release func tries to access some data in bpf_testmod which might > > have been unloaded. The prog_test_ref_kfunc is defined in the kernel, so > > no bpf_testmod btf reference is hold so bpf_testmod can be unloaded before > > bpf_kfunc_call_test_release(). > > As you mentioned, we won't have this issue if bpf_kfunc_call_test_acquire() > > is also in the kernel. > > > > I think putting bpf_kfunc_call_test_acquire() in bpf_testmod and > > bpf_kfunc_call_test_release() in kernel is not a good idea and confusing. > > But since this is only for tests, I guess we can live with that. With that, > > Correct. 65eb006d85a2a ("bpf: Move kernel test kfuncs to bpf_testmod") > also mentions why bpf_kfunc_call_test_release() is not in the module and > states that this is temporary. I'll add a comment in v2 so the wait can > be removed once the functions are re-united. I somehow recall it has to do with the fact you can't have trusted pointer on module's object, so that's why those structs had to stay in kernel.. but I might be wrong jirka > > > Acked-by: Yonghong Song > > > > > --- > > > tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c > > > index 91907b321f913..63f0dbd016703 100644 > > > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c > > > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c > > > @@ -2,6 +2,7 @@ > > > /* Copyright (c) 2020 Facebook */ > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -544,6 +545,9 @@ static int bpf_testmod_init(void) > > > static void bpf_testmod_exit(void) > > > { > > > + while (refcount_read(&prog_test_struct.cnt) > 1) > > > + msleep(20); > > > + > > > return sysfs_remove_bin_file(kernel_kobj, &bin_attr_bpf_testmod_file); > > > } > > > > -- > Regards, > Artem >