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strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().
Direct replacement is safe here since return value of -E2BIG
is used to check for truncation instead of sizeof(dest).
[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89
Link: https://lore.kernel.org/linux-trace-kernel/20230613004125.3539934-1-azeemshaikh38@gmail.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Going a step further, we propose a way to use any user-space
workload as the task waiting for the timerlat timer. This is done
via a per-CPU file named osnoise/cpu$id/timerlat_fd file.
The tracef_fd allows a task to open at a time. When a task reads
the file, the timerlat timer is armed for future osnoise/timerlat_period_us
time. When the timer fires, it prints the IRQ latency and
wakes up the user-space thread waiting in the timerlat_fd.
The thread then starts to run, executes the timerlat measurement, prints
the thread scheduling latency and returns to user-space.
When the thread rereads the timerlat_fd, the tracer will print the
user-ret(urn) latency, which is an additional metric.
This additional metric is also traced by the tracer and can be used, for
example of measuring the context switch overhead from kernel-to-user and
user-to-kernel, or the response time for an arbitrary execution in
user-space.
The tracer supports one thread per CPU, the thread must be pinned to
the CPU, and it cannot migrate while holding the timerlat_fd. The reason
is that the tracer is per CPU (nothing prohibits the tracer from
allowing migrations in the future). The tracer monitors the migration
of the thread and disables the tracer if detected.
The timerlat_fd is only available for opening/reading when timerlat
tracer is enabled, and NO_OSNOISE_WORKLOAD is set.
The simplest way to activate this feature from user-space is:
-------------------------------- %< -----------------------------------
int main(void)
{
char buffer[1024];
int timerlat_fd;
int retval;
long cpu = 0; /* place in CPU 0 */
cpu_set_t set;
CPU_ZERO(&set);
CPU_SET(cpu, &set);
if (sched_setaffinity(gettid(), sizeof(set), &set) == -1)
return 1;
snprintf(buffer, sizeof(buffer),
"/sys/kernel/tracing/osnoise/per_cpu/cpu%ld/timerlat_fd",
cpu);
timerlat_fd = open(buffer, O_RDONLY);
if (timerlat_fd < 0) {
printf("error opening %s: %s\n", buffer, strerror(errno));
exit(1);
}
for (;;) {
retval = read(timerlat_fd, buffer, 1024);
if (retval < 0)
break;
}
close(timerlat_fd);
exit(0);
}
-------------------------------- >% -----------------------------------
When disabling timerlat, if there is a workload holding the timerlat_fd,
the SIGKILL will be sent to the thread.
Link: https://lkml.kernel.org/r/69fe66a863d2792ff4c3a149bf9e32e26468bb3a.1686063934.git.bristot@kernel.org
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: William White <chwhite@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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In the case of all tracing instances being off, sleep for the entire
period.
Q: Why not kill all threads so?
A: It is valid and useful to start the threads with tracing off.
For example, rtla disables tracing, starts the tracer, applies the
scheduling setup to the threads, e.g., sched priority and cgroup,
and then begin tracing with all set.
Skipping the period helps to speed up rtla setup and save the
trace after a stop tracing.
Link: https://lkml.kernel.org/r/aa4dd9b7e76fcb63901fe5407e15ec002b318599.1686063934.git.bristot@kernel.org
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: William White <chwhite@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Currently, osnoise/timerlat threads run with PF_NO_SETAFFINITY set.
It works well, however, cgroups do not allow PF_NO_SETAFFINITY threads
to be accepted, and this creates a limitation to osnoise/timerlat.
To avoid this limitation, disable migration of the threads as soon
as they start to run, and then clean the PF_NO_SETAFFINITY flag (still)
used during thread creation.
If for some reason a thread migration is requested, e.g., via
sched_settafinity, the tracer thread will notice and exit.
Link: https://lkml.kernel.org/r/8ba8bc9c15b3ea40cf73cf67a9bc061a264609f0.1686063934.git.bristot@kernel.org
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: William White <chwhite@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Adding new available_filter_functions_addrs file that shows all available
functions (same as available_filter_functions) together with addresses,
like:
# cat available_filter_functions_addrs | head
ffffffff81000770 __traceiter_initcall_level
ffffffff810007c0 __traceiter_initcall_start
ffffffff81000810 __traceiter_initcall_finish
ffffffff81000860 trace_initcall_finish_cb
...
Note displayed address is the patch-site address and can differ from
/proc/kallsyms address.
It's useful to have address avilable for traceable symbols, so we don't
need to allways cross check kallsyms with available_filter_functions
(or the other way around) and have all the data in single file.
For backwards compatibility reasons we can't change the existing
available_filter_functions file output, but we need to add new file.
The problem is that we need to do 2 passes:
- through available_filter_functions and find out if the function is traceable
- through /proc/kallsyms to get the address for traceable function
Having available_filter_functions symbols together with addresses allow
us to skip the kallsyms step and we are ok with the address in
available_filter_functions_addr not being the function entry, because
kprobe_multi uses fprobe and that handles both entry and patch-site
address properly.
We have 2 interfaces how to create kprobe_multi link:
a) passing symbols to kernel
1) user gathers symbols and need to ensure that they are
trace-able -> pass through available_filter_functions file
2) kernel takes those symbols and translates them to addresses
through kallsyms api
3) addresses are passed to fprobe/ftrace through:
register_fprobe_ips
-> ftrace_set_filter_ips
b) passing addresses to kernel
1) user gathers symbols and needs to ensure that they are
trace-able -> pass through available_filter_functions file
2) user takes those symbols and translates them to addresses
through /proc/kallsyms
3) addresses are passed to the kernel and kernel calls:
register_fprobe_ips
-> ftrace_set_filter_ips
The new available_filter_functions_addrs file helps us with option b),
because we can make 'b 1' and 'b 2' in one step - while filtering traceable
functions, we get the address directly.
Link: https://lore.kernel.org/linux-trace-kernel/20230611130029.1202298-1-jolsa@kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Tested-by: Jackie Liu <liuyun01@kylinos.cn> # x86
Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Azeem Shaikh
Daniel Bristot de Oliveira
Jiri Olsa