Linux-kselftest-mirror September 2020

linux-kselftest-mirror@lists.linaro.org

103 participants
113 discussions

by Christian Brauner

Hi, Passing a non-blocking pidfd to waitid() currently has no effect, i.e. is not supported. There are users which would like to use waitid() on pidfds that are O_NONBLOCK and mix it with pidfds that are blocking and both pass them to waitid(). The expected behavior is to have waitid() return -EAGAIN for non-blocking pidfds and to block for blocking pidfds without needing to perform any additional checks for flags set on the pidfd before passing it to waitid(). Non-blocking pidfds will return EAGAIN from waitid() when no child process is ready yet. Returning -EAGAIN for non-blocking pidfds makes it easier for event loops that handle EAGAIN specially. It also makes the API more consistent and uniform. In essence, waitid() is treated like a read on a non-blocking pidfd or a recvmsg() on a non-blocking socket. With the addition of support for non-blocking pidfds we support the same functionality that sockets do. For sockets() recvmsg() supports MSG_DONTWAIT for pidfds waitid() supports WNOHANG. Both flags are per-call options. In contrast non-blocking pidfds and non-blocking sockets are a setting on an open file description affecting all threads in the calling process as well as other processes that hold file descriptors referring to the same open file description. Both behaviors, per call and per open file description, have genuine use-cases. A concrete use-case that was brought on-list (see [1]) was Josh's async pidfd library. Ever since the introduction of pidfds and more advanced async io various programming languages such as Rust have grown support for async event libraries. These libraries are created to help build epoll-based event loops around file descriptors. A common pattern is to automatically make all file descriptors they manage to O_NONBLOCK. For such libraries the EAGAIN error code is treated specially. When a function is called that returns EAGAIN the function isn't called again until the event loop indicates the the file descriptor is ready. Supporting EAGAIN when waiting on pidfds makes such libraries just work with little effort. Thanks! Christian [1]: https://lore.kernel.org/lkml/20200811181236.GA18763@localhost/ Christian Brauner (4): pidfd: support PIDFD_NONBLOCK in pidfd_open() exit: support non-blocking pidfds tests: port pidfd_wait to kselftest harness tests: add waitid() tests for non-blocking pidfds include/uapi/linux/pidfd.h | 12 + kernel/exit.c | 19 +- kernel/pid.c | 12 +- tools/testing/selftests/pidfd/pidfd.h | 4 + tools/testing/selftests/pidfd/pidfd_wait.c | 298 +++++++++------------ 5 files changed, 161 insertions(+), 184 deletions(-) create mode 100644 include/uapi/linux/pidfd.h base-commit: d012a7190fc1fd72ed48911e77ca97ba4521bccd -- 2.28.0

3 years, 7 months

[PATCH] selftests: vm: add fragment CONFIG_GUP_BENCHMARK

by Anatoly Pugachev

When running gup_benchmark test the following output states that the config options is missing. $ sudo ./gup_benchmark open: No such file or directory $ sudo strace -e trace=file ./gup_benchmark 2>&1 | tail -3 openat(AT_FDCWD, "/sys/kernel/debug/gup_benchmark", O_RDWR) = -1 ENOENT (No such file or directory) open: No such file or directory +++ exited with 1 +++ Fix it by adding config option fragment. Fixes: 64c349f4ae78 ("mm: add infrastructure for get_user_pages_fast() benchmarking") Signed-off-by: Anatoly Pugachev <matorola(a)gmail.com> CC: Jiri Kosina <trivial(a)kernel.org> CC: Shuah Khan <shuah(a)kernel.org> --- tools/testing/selftests/vm/config | 1 + 1 file changed, 1 insertion(+) diff --git a/tools/testing/selftests/vm/config b/tools/testing/selftests/vm/config index 3ba674b64fa9..69dd0d1aa30b 100644 --- a/tools/testing/selftests/vm/config +++ b/tools/testing/selftests/vm/config @@ -3,3 +3,4 @@ CONFIG_USERFAULTFD=y CONFIG_TEST_VMALLOC=m CONFIG_DEVICE_PRIVATE=y CONFIG_TEST_HMM=m +CONFIG_GUP_BENCHMARK=y -- 2.27.0

3 years, 7 months

[PATCH v3 0/5] arm64: vdso: getcpu() support

by Mark Brown

Some applications, especially tracing ones, benefit from avoiding the syscall overhead for getcpu() so it is common for architectures to have vDSO implementations. Add one for arm64, using TPIDRRO_EL0 to pass a pointer to per-CPU data rather than just store the immediate value in order to allow for future extensibility. It is questionable if something TPIDRRO_EL0 based is worthwhile at all on current kernels, since v4.18 we have had support for restartable sequences which can be used to provide a sched_getcpu() implementation with generally better performance than the vDSO approach on architectures which have that[1]. Work is ongoing to implement this for glibc: https://lore.kernel.org/lkml/20200527185130.5604-3-mathieu.desnoyers@effici… but is not yet merged and will need similar work for other userspaces. The main advantages for the vDSO implementation are the node parameter (though this is a static mapping to CPU number so could be looked up separately when processing data if it's needed, it shouldn't need to be in the hot path) and ease of implementation for users. This is currently not compatible with KPTI due to the use of TPIDRRO_EL0 by the KPTI trampoline, this could be addressed by reinitializing that system register in the return path but I have found it hard to justify adding that overhead for all users for something that is essentially a profiling optimization which is likely to get superceeded by a more modern implementation - if there are other uses for the per-CPU data then the balance might change here. This builds on work done by Kristina Martsenko some time ago but is a new implementation. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?… v3: - Rebase on v5.9-rc1. - Drop in progress portions of the series. v2: - Rebase on v5.8-rc3. - Add further cleanup patches & a first draft of multi-page support. Mark Brown (5): arm64: vdso: Provide a define when building the vDSO arm64: vdso: Add per-CPU data arm64: vdso: Initialise the per-CPU vDSO data arm64: vdso: Add getcpu() implementation selftests: vdso: Support arm64 in getcpu() test arch/arm64/include/asm/processor.h | 12 +---- arch/arm64/include/asm/vdso/datapage.h | 54 +++++++++++++++++++ arch/arm64/kernel/process.c | 26 ++++++++- arch/arm64/kernel/vdso.c | 33 +++++++++++- arch/arm64/kernel/vdso/Makefile | 4 +- arch/arm64/kernel/vdso/vdso.lds.S | 1 + arch/arm64/kernel/vdso/vgetcpu.c | 48 +++++++++++++++++ .../testing/selftests/vDSO/vdso_test_getcpu.c | 10 ++++ 8 files changed, 172 insertions(+), 16 deletions(-) create mode 100644 arch/arm64/include/asm/vdso/datapage.h create mode 100644 arch/arm64/kernel/vdso/vgetcpu.c -- 2.20.1

3 years, 7 months

2024

2023

2022

2021

2020

2019

2018

2017

Linux-kselftest-mirror September 2020