| Message ID | 20241003211716.371786-2-edliaw@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | selftests/mm: fix deadlock after pthread_create | expand |
On 10/4/24 2:17 AM, 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 <edliaw@google.com> Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com> > --- > 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); > > 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 <inttypes.h> > #include <stdint.h> > #include <sys/random.h> > -#include <stdatomic.h> > > #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)
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 <edliaw@google.com> > --- > 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 <inttypes.h> > #include <stdint.h> > #include <sys/random.h> > -#include <stdatomic.h> > > #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)
On Fri, Oct 18, 2024 at 7:37 AM Ryan Roberts <ryan.roberts@arm.com> wrote: > > 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 <edliaw@google.com> > > --- > > 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. Ah, I should not have changed it to a pthread_barrier, since that depends on the parent creating the barrier; I'm sending a revert and subsequent fix. > > 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 <inttypes.h> > > #include <stdint.h> > > #include <sys/random.h> > > -#include <stdatomic.h> > > > > #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) >
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); 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 <inttypes.h> #include <stdint.h> #include <sys/random.h> -#include <stdatomic.h> #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)
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 <edliaw@google.com> --- 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(-)