The perf subsystem today unifies various tracing and monitoring
features, from both software and hardware. One benefit of the perf
subsystem is automatically inheriting events to child tasks, which
enables process-wide events monitoring with low overheads. By default
perf events are non-intrusive, not affecting behaviour of the tasks
being monitored.
For certain use-cases, however, it makes sense to leverage the
generality of the perf events subsystem and optionally allow the tasks
being monitored to receive signals on events they are interested in.
This patch series adds the option to synchronously signal user space on
events.
To better support process-wide synchronous self-monitoring, without
events propagating to children that do not share the current process's
shared environment, two pre-requisite patches are added to optionally
restrict inheritance to CLONE_THREAD, and remove events on exec (without
affecting the parent).
Examples how to use these features can be found in the tests added at
the end of the series. In addition to the tests added, the series has
also been subjected to syzkaller fuzzing (focus on 'kernel/events/'
coverage).
Motivation and Example Uses
---------------------------
1. Our immediate motivation is low-overhead sampling-based race
detection for user space [1]. By using perf_event_open() at
process initialization, we can create hardware
breakpoint/watchpoint events that are propagated automatically
to all threads in a process. As far as we are aware, today no
existing kernel facility (such as ptrace) allows us to set up
process-wide watchpoints with minimal overheads (that are
comparable to mprotect() of whole pages).
2. Other low-overhead error detectors that rely on detecting
accesses to certain memory locations or code, process-wide and
also only in a specific set of subtasks or threads.
[1] https://llvm.org/devmtg/2020-09/slides/Morehouse-GWP-Tsan.pdf
Other ideas for use-cases we found interesting, but should only
illustrate the range of potential to further motivate the utility (we're
sure there are more):
3. Code hot patching without full stop-the-world. Specifically, by
setting a code breakpoint to entry to the patched routine, then
send signals to threads and check that they are not in the
routine, but without stopping them further. If any of the
threads will enter the routine, it will receive SIGTRAP and
pause.
4. Safepoints without mprotect(). Some Java implementations use
"load from a known memory location" as a safepoint. When threads
need to be stopped, the page containing the location is
mprotect()ed and threads get a signal. This could be replaced with
a watchpoint, which does not require a whole page nor DTLB
shootdowns.
5. Threads receiving signals on performance events to
throttle/unthrottle themselves.
6. Tracking data flow globally.
Changelog
---------
v4:
* Fix for parent and child racing to exit in sync_child_event().
* Fix race between irq_work running and task's sighand being released by
release_task().
* Generalize setting si_perf and si_addr independent of event type;
introduces perf_event_attr::sig_data, which can be set by user space
to be propagated to si_perf.
* Warning in perf_sigtrap() if ctx->task and current mismatch; we expect
this on architectures that do not properly implement
arch_irq_work_raise().
* Require events that want sigtrap to be associated with a task.
* Dropped "perf: Add breakpoint information to siginfo on SIGTRAP"
in favor of more generic solution (perf_event_attr::sig_data).
v3:
* Add patch "perf: Rework perf_event_exit_event()" to beginning of
series, courtesy of Peter Zijlstra.
* Rework "perf: Add support for event removal on exec" based on
the added "perf: Rework perf_event_exit_event()".
* Fix kselftests to work with more recent libc, due to the way it forces
using the kernel's own siginfo_t.
* Add basic perf-tool built-in test.
v2/RFC: https://lkml.kernel.org/r/20210310104139.679618-1-elver@google.com
* Patch "Support only inheriting events if cloned with CLONE_THREAD"
added to series.
* Patch "Add support for event removal on exec" added to series.
* Patch "Add kselftest for process-wide sigtrap handling" added to
series.
* Patch "Add kselftest for remove_on_exec" added to series.
* Implicitly restrict inheriting events if sigtrap, but the child was
cloned with CLONE_CLEAR_SIGHAND, because it is not generally safe if
the child cleared all signal handlers to continue sending SIGTRAP.
* Various minor fixes (see details in patches).
v1/RFC: https://lkml.kernel.org/r/20210223143426.2412737-1-elver@google.com
Pre-series: The discussion at [2] led to the changes in this series. The
approach taken in "Add support for SIGTRAP on perf events" to trigger
the signal was suggested by Peter Zijlstra in [3].
[2] https://lore.kernel.org/lkml/CACT4Y+YPrXGw+AtESxAgPyZ84TYkNZdP0xpocX2jwVAbZ…
[3] https://lore.kernel.org/lkml/YBv3rAT566k+6zjg@hirez.programming.kicks-ass.n…
Marco Elver (9):
perf: Apply PERF_EVENT_IOC_MODIFY_ATTRIBUTES to children
perf: Support only inheriting events if cloned with CLONE_THREAD
perf: Add support for event removal on exec
signal: Introduce TRAP_PERF si_code and si_perf to siginfo
perf: Add support for SIGTRAP on perf events
selftests/perf_events: Add kselftest for process-wide sigtrap handling
selftests/perf_events: Add kselftest for remove_on_exec
tools headers uapi: Sync tools/include/uapi/linux/perf_event.h
perf test: Add basic stress test for sigtrap handling
Peter Zijlstra (1):
perf: Rework perf_event_exit_event()
arch/m68k/kernel/signal.c | 3 +
arch/x86/kernel/signal_compat.c | 5 +-
fs/signalfd.c | 4 +
include/linux/compat.h | 2 +
include/linux/perf_event.h | 9 +-
include/linux/signal.h | 1 +
include/uapi/asm-generic/siginfo.h | 6 +-
include/uapi/linux/perf_event.h | 12 +-
include/uapi/linux/signalfd.h | 4 +-
kernel/events/core.c | 302 +++++++++++++-----
kernel/fork.c | 2 +-
kernel/signal.c | 11 +
tools/include/uapi/linux/perf_event.h | 12 +-
tools/perf/tests/Build | 1 +
tools/perf/tests/builtin-test.c | 5 +
tools/perf/tests/sigtrap.c | 150 +++++++++
tools/perf/tests/tests.h | 1 +
.../testing/selftests/perf_events/.gitignore | 3 +
tools/testing/selftests/perf_events/Makefile | 6 +
tools/testing/selftests/perf_events/config | 1 +
.../selftests/perf_events/remove_on_exec.c | 260 +++++++++++++++
tools/testing/selftests/perf_events/settings | 1 +
.../selftests/perf_events/sigtrap_threads.c | 210 ++++++++++++
23 files changed, 924 insertions(+), 87 deletions(-)
create mode 100644 tools/perf/tests/sigtrap.c
create mode 100644 tools/testing/selftests/perf_events/.gitignore
create mode 100644 tools/testing/selftests/perf_events/Makefile
create mode 100644 tools/testing/selftests/perf_events/config
create mode 100644 tools/testing/selftests/perf_events/remove_on_exec.c
create mode 100644 tools/testing/selftests/perf_events/settings
create mode 100644 tools/testing/selftests/perf_events/sigtrap_threads.c
--
2.31.0.208.g409f899ff0-goog
Hi all,
following bug is trying to workaround an error on ppc64le, where
zram01.sh LTP test (there is also kernel selftest
tools/testing/selftests/zram/zram01.sh, but LTP test got further
updates) has often mem_used_total 0 although zram is already filled.
Patch tries to repeatedly read /sys/block/zram*/mm_stat for 1 sec,
waiting for mem_used_total > 0. The question if this is expected and
should be workarounded or a bug which should be fixed.
REPRODUCE THE ISSUE
Quickest way to install only zram tests and their dependencies:
make autotools && ./configure && for i in testcases/lib/ testcases/kernel/device-drivers/zram/; do cd $i && make -j$(getconf _NPROCESSORS_ONLN) && make install && cd -; done
Run the test (only on vfat)
PATH="/opt/ltp/testcases/bin:$PATH" LTP_SINGLE_FS_TYPE=vfat zram01.sh
Petr Vorel (1):
zram01.sh: Workaround division by 0 on vfat on ppc64le
.../kernel/device-drivers/zram/zram01.sh | 27 +++++++++++++++++--
1 file changed, 25 insertions(+), 2 deletions(-)
--
2.38.0
I checked and the Landlock ptrace test failed because Yama is enabled,
which is expected. You can check that with
/proc/sys/kernel/yama/ptrace_scope
Jeff Xu sent a patch to fix this case but it is not ready yet:
https://lore.kernel.org/r/20220628222941.2642917-1-jeffxu@google.com
Could you please send a new patch Jeff, and add Limin in Cc?
On 29/11/2022 12:26, limin wrote:
> cat /proc/cmdline
> BOOT_IMAGE=/vmlinuz-6.1.0-next-20221116
> root=UUID=a65b3a79-dc02-4728-8a0c-5cf24f4ae08b ro
> systemd.unified_cgroup_hierarchy=1 cgroup_no_v1=all
>
>
> config
>
> #
> # Automatically generated file; DO NOT EDIT.
> # Linux/x86 6.1.0-rc6 Kernel Configuration
> #
[...]
> CONFIG_SECURITY_YAMA=y
[...]
> CONFIG_LSM="landlock,lockdown,yama,integrity,apparmor"
[...]
>
> On 2022/11/29 19:03, Mickaël Salaün wrote:
>> I tested with next-20221116 and all tests are OK. Could you share your
>> kernel configuration with a link? What is the content of /proc/cmdline?
>>
>> On 29/11/2022 02:42, limin wrote:
>>> I run test on Linux ubuntu2204 6.1.0-next-20221116
>>>
>>> I did't use yama.
>>>
>>> you can reproduce by this step:
>>>
>>> cd kernel_src
>>>
>>> cd tools/testing/selftests/landlock/
>>> make
>>> ./ptrace_test
>>>
>>>
>>>
>>>
>>> On 2022/11/29 3:44, Mickaël Salaün wrote:
>>>> This patch changes the test semantic and then cannot work on my test
>>>> environment. On which kernel did you run test? Do you use Yama or
>>>> something similar?
>>>>
>>>> On 28/11/2022 03:04, limin wrote:
>>>>> Tests PTRACE_ATTACH and PTRACE_MODE_READ on the parent,
>>>>> trace parent return -1 when child== 0
>>>>> How to reproduce warning:
>>>>> $ make -C tools/testing/selftests TARGETS=landlock run_tests
>>>>>
>>>>> Signed-off-by: limin <limin100(a)huawei.com>
>>>>> ---
>>>>> tools/testing/selftests/landlock/ptrace_test.c | 5 ++---
>>>>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/tools/testing/selftests/landlock/ptrace_test.c
>>>>> b/tools/testing/selftests/landlock/ptrace_test.c
>>>>> index c28ef98ff3ac..88c4dc63eea0 100644
>>>>> --- a/tools/testing/selftests/landlock/ptrace_test.c
>>>>> +++ b/tools/testing/selftests/landlock/ptrace_test.c
>>>>> @@ -267,12 +267,11 @@ TEST_F(hierarchy, trace)
>>>>> /* Tests PTRACE_ATTACH and PTRACE_MODE_READ on the
>>>>> parent. */
>>>>> err_proc_read = test_ptrace_read(parent);
>>>>> ret = ptrace(PTRACE_ATTACH, parent, NULL, 0);
>>>>> + EXPECT_EQ(-1, ret);
>>>>> + EXPECT_EQ(EPERM, errno);
>>>>> if (variant->domain_child) {
>>>>> - EXPECT_EQ(-1, ret);
>>>>> - EXPECT_EQ(EPERM, errno);
>>>>> EXPECT_EQ(EACCES, err_proc_read);
>>>>> } else {
>>>>> - EXPECT_EQ(0, ret);
>>>>> EXPECT_EQ(0, err_proc_read);
>>>>> }
>>>>> if (ret == 0) {