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Subject[RFC PATCH for 4.18 00/14] Restartable Sequences
Date
Hi,

Here is an updated RFC round of the Restartable Sequences patchset
based on kernel 4.17-rc3. Based on feedback from Linus, I'm introducing
only the rseq system call, keeping the rest for later.

This already enables speeding up the Facebook jemalloc and arm64 PMC
read from user-space use-cases, as well as speedup of use-cases relying
on getting the current cpu number from user-space. We'll have to wait
until a more complete solution is introduced before the LTTng-UST
tracer can replace its ring buffer atomic instructions with rseq
though. But let's proceed one step at a time.

The main change introduced by the removal of cpu_opv from this series
in terms of library use from user-space is that APIs that previously
took a CPU number as argument now only act on the current CPU.

So for instance, this turns:

int cpu = rseq_per_cpu_lock(lock, target_cpu);
[...]
rseq_per_cpu_unlock(lock, cpu);

into

int cpu = rseq_this_cpu_lock(lock);
[...]
rseq_per_cpu_unlock(lock, cpu);

and:

per_cpu_list_push(list, node, target_cpu);
[...]
per_cpu_list_pop(list, node, target_cpu);

into

this_cpu_list_push(list, node, &cpu); /* cpu is an output parameter. */
[...]
node = this_cpu_list_pop(list, &cpu); /* cpu is an output parameter. */

Eventually integrating cpu_opv or some alternative will allow passing
the cpu number as parameter rather than requiring the algorithm to work
on the current CPU.

The second effect of not having the cpu_opv fallback is that
line and instruction single-stepping with a debugger transforms rseq
critical sections based on retry loops into never-ending loops.
Debuggers need to use the __rseq_table section to skip those critical
sections in order to correctly behave when single-stepping a thread
which uses rseq in a retry loop. However, applications which use an
alternative fallback method rather than retrying on rseq fast-path abort
won't be affected by this kind of single-stepping issue.

Feedback is welcome!

Thanks,

Mathieu

Boqun Feng (2):
powerpc: Add support for restartable sequences
powerpc: Wire up restartable sequences system call

Mathieu Desnoyers (12):
uapi headers: Provide types_32_64.h (v2)
rseq: Introduce restartable sequences system call (v13)
arm: Add restartable sequences support
arm: Wire up restartable sequences system call
x86: Add support for restartable sequences (v2)
x86: Wire up restartable sequence system call
selftests: lib.mk: Introduce OVERRIDE_TARGETS
rseq: selftests: Provide rseq library (v5)
rseq: selftests: Provide basic test
rseq: selftests: Provide basic percpu ops test (v2)
rseq: selftests: Provide parametrized tests (v2)
rseq: selftests: Provide Makefile, scripts, gitignore (v2)

MAINTAINERS | 12 +
arch/Kconfig | 7 +
arch/arm/Kconfig | 1 +
arch/arm/kernel/signal.c | 7 +
arch/arm/tools/syscall.tbl | 1 +
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/systbl.h | 1 +
arch/powerpc/include/asm/unistd.h | 2 +-
arch/powerpc/include/uapi/asm/unistd.h | 1 +
arch/powerpc/kernel/signal.c | 3 +
arch/x86/Kconfig | 1 +
arch/x86/entry/common.c | 3 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/x86/kernel/signal.c | 6 +
fs/exec.c | 1 +
include/linux/sched.h | 134 +++
include/linux/syscalls.h | 4 +-
include/trace/events/rseq.h | 56 +
include/uapi/linux/rseq.h | 150 +++
include/uapi/linux/types_32_64.h | 67 ++
init/Kconfig | 23 +
kernel/Makefile | 1 +
kernel/fork.c | 2 +
kernel/rseq.c | 366 ++++++
kernel/sched/core.c | 2 +
kernel/sys_ni.c | 3 +
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/lib.mk | 4 +
tools/testing/selftests/rseq/.gitignore | 6 +
tools/testing/selftests/rseq/Makefile | 29 +
.../testing/selftests/rseq/basic_percpu_ops_test.c | 312 +++++
tools/testing/selftests/rseq/basic_test.c | 55 +
tools/testing/selftests/rseq/param_test.c | 1259 ++++++++++++++++++++
tools/testing/selftests/rseq/rseq-arm.h | 732 ++++++++++++
tools/testing/selftests/rseq/rseq-ppc.h | 688 +++++++++++
tools/testing/selftests/rseq/rseq-skip.h | 82 ++
tools/testing/selftests/rseq/rseq-x86.h | 1149 ++++++++++++++++++
tools/testing/selftests/rseq/rseq.c | 116 ++
tools/testing/selftests/rseq/rseq.h | 164 +++
tools/testing/selftests/rseq/run_param_test.sh | 120 ++
41 files changed, 5572 insertions(+), 2 deletions(-)
create mode 100644 include/trace/events/rseq.h
create mode 100644 include/uapi/linux/rseq.h
create mode 100644 include/uapi/linux/types_32_64.h
create mode 100644 kernel/rseq.c
create mode 100644 tools/testing/selftests/rseq/.gitignore
create mode 100644 tools/testing/selftests/rseq/Makefile
create mode 100644 tools/testing/selftests/rseq/basic_percpu_ops_test.c
create mode 100644 tools/testing/selftests/rseq/basic_test.c
create mode 100644 tools/testing/selftests/rseq/param_test.c
create mode 100644 tools/testing/selftests/rseq/rseq-arm.h
create mode 100644 tools/testing/selftests/rseq/rseq-ppc.h
create mode 100644 tools/testing/selftests/rseq/rseq-skip.h
create mode 100644 tools/testing/selftests/rseq/rseq-x86.h
create mode 100644 tools/testing/selftests/rseq/rseq.c
create mode 100644 tools/testing/selftests/rseq/rseq.h
create mode 100755 tools/testing/selftests/rseq/run_param_test.sh

--
2.11.0

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