From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 94353768E1; Fri, 18 Oct 2024 14:37:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729262248; cv=none; b=hdVbao/Md8d5qg4CpV1At8OzKKAg3L8RjVTQYDWKj9iSUwqYcB/eNe3yMDQE+U7MgEy7ddiFbyf0VMnkyXqEQ9ZVoHY90A+WaACdTBtRoE1MsJ6sEUelgZrCwiWQrDqwkaPjeFy8r51dVMPDfajCWvf47bHSl5PyeBLd+QcZSC0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729262248; c=relaxed/simple; bh=A0Qe57BA5SKFuEpfXr/0vVf3iraWpCGMTe6Ux26pQBA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=N52ckIcDOYdcZPz685S+J0HwBX8TxW9gF3R0FEWqfz77KnKGclG9rHPe80L4qAbkSHbUcaImWQHkfRMo+Oyh5S3bQQoZRabpPLn76NUXmm02V0N8E+ZqC7CI31lQ1kgSmwceibDVUAppIMwg0Ce72AZdJsIoiRF7AYC4658vAIM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6765FDA7; Fri, 18 Oct 2024 07:37:55 -0700 (PDT) Received: from [10.57.87.223] (unknown [10.57.87.223]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2DC163F58B; Fri, 18 Oct 2024 07:37:24 -0700 (PDT) Message-ID: Date: Fri, 18 Oct 2024 15:37:22 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] selftests/mm: replace atomic_bool with pthread_barrier_t Content-Language: en-GB To: Edward Liaw , linux-kselftest@vger.kernel.org, Andrew Morton , Shuah Khan , Lokesh Gidra , Peter Xu Cc: linux-kernel@vger.kernel.org, kernel-team@android.com, linux-mm@kvack.org, Aishwarya TCV References: <20241003211716.371786-1-edliaw@google.com> <20241003211716.371786-2-edliaw@google.com> From: Ryan Roberts In-Reply-To: <20241003211716.371786-2-edliaw@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 03/10/2024 22:17, Edward Liaw wrote: > Swaps synchronization primitive with pthread_barrier, so that > stdatomic.h does not need to be included. > > The synchronization is needed on Android ARM64; we see a deadlock with > pthread_create when the parent thread races forward before the child has > a chance to start doing work. > > Fixes: 8c864371b2a1 ("selftests/mm: fix ARM related issue with fork after > pthread_create") > Signed-off-by: Edward Liaw > --- > tools/testing/selftests/mm/uffd-common.c | 5 +++-- > tools/testing/selftests/mm/uffd-common.h | 3 +-- > tools/testing/selftests/mm/uffd-unit-tests.c | 14 ++++++++------ > 3 files changed, 12 insertions(+), 10 deletions(-) > > diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c > index 717539eddf98..852e7281026e 100644 > --- a/tools/testing/selftests/mm/uffd-common.c > +++ b/tools/testing/selftests/mm/uffd-common.c > @@ -18,7 +18,7 @@ bool test_uffdio_wp = true; > unsigned long long *count_verify; > uffd_test_ops_t *uffd_test_ops; > uffd_test_case_ops_t *uffd_test_case_ops; > -atomic_bool ready_for_fork; > +pthread_barrier_t ready_for_fork; > > static int uffd_mem_fd_create(off_t mem_size, bool hugetlb) > { > @@ -519,7 +519,8 @@ void *uffd_poll_thread(void *arg) > pollfd[1].fd = pipefd[cpu*2]; > pollfd[1].events = POLLIN; > > - ready_for_fork = true; > + /* Ready for parent thread to fork */ > + pthread_barrier_wait(&ready_for_fork); Hi Edward, This change is causing uffd-unit-tests to hang on arm64 when running the "move on anon" test. It's happening because this wait is never returning for this case. And that happens because ready_for_fork was never initialized for this test. It looks like there are other places where a thread is created for uffd_poll_thread() where ready_for_fork is not initialized too. I added this change and it solves the problem, although it's pretty hacky. This is blocking our arm64 testing on linux-next so would appreciate either a quick fix or removing the change until a fix is ready. Thanks, Ryan ----8<----- diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c index 852e7281026e..a05eb705be02 100644 --- a/tools/testing/selftests/mm/uffd-common.c +++ b/tools/testing/selftests/mm/uffd-common.c @@ -19,6 +19,7 @@ unsigned long long *count_verify; uffd_test_ops_t *uffd_test_ops; uffd_test_case_ops_t *uffd_test_case_ops; pthread_barrier_t ready_for_fork; +bool wait_ready_for_fork; static int uffd_mem_fd_create(off_t mem_size, bool hugetlb) { @@ -520,7 +521,8 @@ void *uffd_poll_thread(void *arg) pollfd[1].events = POLLIN; /* Ready for parent thread to fork */ - pthread_barrier_wait(&ready_for_fork); + if (wait_ready_for_fork) + pthread_barrier_wait(&ready_for_fork); for (;;) { ret = poll(pollfd, 2, -1); diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h index 3e6228d8e0dc..e94329a39b34 100644 --- a/tools/testing/selftests/mm/uffd-common.h +++ b/tools/testing/selftests/mm/uffd-common.h @@ -105,6 +105,7 @@ extern bool test_uffdio_wp; extern unsigned long long *count_verify; extern volatile bool test_uffdio_copy_eexist; extern pthread_barrier_t ready_for_fork; +extern bool wait_ready_for_fork; extern uffd_test_ops_t anon_uffd_test_ops; extern uffd_test_ops_t shmem_uffd_test_ops; diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c index 3db2296ac631..d1fc4cd6a948 100644 --- a/tools/testing/selftests/mm/uffd-unit-tests.c +++ b/tools/testing/selftests/mm/uffd-unit-tests.c @@ -775,6 +775,7 @@ static void uffd_sigbus_test_common(bool wp) struct uffd_args args = { 0 }; pthread_barrier_init(&ready_for_fork, NULL, 2); + wait_ready_for_fork = true; fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK); @@ -794,6 +795,7 @@ static void uffd_sigbus_test_common(bool wp) /* Wait for child thread to start before forking */ pthread_barrier_wait(&ready_for_fork); pthread_barrier_destroy(&ready_for_fork); + wait_ready_for_fork = false; pid = fork(); if (pid < 0) @@ -835,6 +837,7 @@ static void uffd_events_test_common(bool wp) struct uffd_args args = { 0 }; pthread_barrier_init(&ready_for_fork, NULL, 2); + wait_ready_for_fork = true; fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK); if (uffd_register(uffd, area_dst, nr_pages * page_size, @@ -848,6 +851,7 @@ static void uffd_events_test_common(bool wp) /* Wait for child thread to start before forking */ pthread_barrier_wait(&ready_for_fork); pthread_barrier_destroy(&ready_for_fork); + wait_ready_for_fork = false; pid = fork(); if (pid < 0) ----8<----- > > for (;;) { > ret = poll(pollfd, 2, -1); > diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h > index a70ae10b5f62..3e6228d8e0dc 100644 > --- a/tools/testing/selftests/mm/uffd-common.h > +++ b/tools/testing/selftests/mm/uffd-common.h > @@ -33,7 +33,6 @@ > #include > #include > #include > -#include > > #include "../kselftest.h" > #include "vm_util.h" > @@ -105,7 +104,7 @@ extern bool map_shared; > extern bool test_uffdio_wp; > extern unsigned long long *count_verify; > extern volatile bool test_uffdio_copy_eexist; > -extern atomic_bool ready_for_fork; > +extern pthread_barrier_t ready_for_fork; > > extern uffd_test_ops_t anon_uffd_test_ops; > extern uffd_test_ops_t shmem_uffd_test_ops; > diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c > index b3d21eed203d..3db2296ac631 100644 > --- a/tools/testing/selftests/mm/uffd-unit-tests.c > +++ b/tools/testing/selftests/mm/uffd-unit-tests.c > @@ -774,7 +774,7 @@ static void uffd_sigbus_test_common(bool wp) > char c; > struct uffd_args args = { 0 }; > > - ready_for_fork = false; > + pthread_barrier_init(&ready_for_fork, NULL, 2); > > fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK); > > @@ -791,8 +791,9 @@ static void uffd_sigbus_test_common(bool wp) > if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) > err("uffd_poll_thread create"); > > - while (!ready_for_fork) > - ; /* Wait for the poll_thread to start executing before forking */ > + /* Wait for child thread to start before forking */ > + pthread_barrier_wait(&ready_for_fork); > + pthread_barrier_destroy(&ready_for_fork); > > pid = fork(); > if (pid < 0) > @@ -833,7 +834,7 @@ static void uffd_events_test_common(bool wp) > char c; > struct uffd_args args = { 0 }; > > - ready_for_fork = false; > + pthread_barrier_init(&ready_for_fork, NULL, 2); > > fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK); > if (uffd_register(uffd, area_dst, nr_pages * page_size, > @@ -844,8 +845,9 @@ static void uffd_events_test_common(bool wp) > if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args)) > err("uffd_poll_thread create"); > > - while (!ready_for_fork) > - ; /* Wait for the poll_thread to start executing before forking */ > + /* Wait for child thread to start before forking */ > + pthread_barrier_wait(&ready_for_fork); > + pthread_barrier_destroy(&ready_for_fork); > > pid = fork(); > if (pid < 0)