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tracing/kprobes: expose maxactive for kretprobe in kprobe_events 

When a kretprobe is installed on a kernel function, there is a maximum
limit of how many calls in parallel it can catch (aka "maxactive"). A
kernel module could call register_kretprobe() and initialize maxactive
(see example in samples/kprobes/kretprobe_example.c).

But that is not exposed to userspace and it is currently not possible to
choose maxactive when writing to /sys/kernel/debug/tracing/kprobe_events

The default maxactive can be as low as 1 on single-core with a
non-preemptive kernel. This is too low and we need to increase it not
only for recursive functions, but for functions that sleep or resched.

This patch updates the format of the command that can be written to
kprobe_events so that maxactive can be optionally specified.

I need this for a bpf program attached to the kretprobe of
inet_csk_accept, which can sleep for a long time.

This patch includes a basic selftest:

> # ./ftracetest -v  test.d/kprobe/
> === Ftrace unit tests ===
> [1] Kprobe dynamic event - adding and removing	[PASS]
> [2] Kprobe dynamic event - busy event check	[PASS]
> [3] Kprobe dynamic event with arguments	[PASS]
> [4] Kprobes event arguments with types	[PASS]
> [5] Kprobe dynamic event with function tracer	[PASS]
> [6] Kretprobe dynamic event with arguments	[PASS]
> [7] Kretprobe dynamic event with maxactive	[PASS]
>
> # of passed:  7
> # of failed:  0
> # of unresolved:  0
> # of untested:  0
> # of unsupported:  0
> # of xfailed:  0
> # of undefined(test bug):  0

BugLink: https://github.com/iovisor/bcc/issues/1072
Link: http://lkml.kernel.org/r/1491215782-15490-1-git-send-email-alban@kinvolk.io

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Alban Crequy <alban@kinvolk.io>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
hifive-unleashed-5.1
Alban Crequy 2017-04-03 12:36:22 +02:00 committed by Steven Rostedt (VMware)
parent b80f0f6c9e
commit 696ced4fb1
3 changed files with 76 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
Documentation/trace/kprobetrace.txt
View File

@ -23,7 +23,7 @@ current_tracer. Instead of that, add probe points via
Synopsis of kprobe_events
-------------------------
p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe
r[:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe
r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe
-:[GRP/]EVENT : Clear a probe
GRP : Group name. If omitted, use "kprobes" for it.
@ -32,6 +32,9 @@ Synopsis of kprobe_events
MOD : Module name which has given SYM.
SYM[+offs] : Symbol+offset where the probe is inserted.
MEMADDR : Address where the probe is inserted.
MAXACTIVE : Maximum number of instances of the specified function that
can be probed simultaneously, or 0 for the default value
as defined in Documentation/kprobes.txt section 1.3.1.
FETCHARGS : Arguments. Each probe can have up to 128 args.
%REG : Fetch register REG

39
kernel/trace/trace_kprobe.c
View File

@ -25,6 +25,7 @@
#include "trace_probe.h"
#define KPROBE_EVENT_SYSTEM "kprobes"
#define KRETPROBE_MAXACTIVE_MAX 4096
/**
* Kprobe event core functions
@ -282,6 +283,7 @@ static struct trace_kprobe *alloc_trace_kprobe(const char *group,
void *addr,
const char *symbol,
unsigned long offs,
int maxactive,
int nargs, bool is_return)
{
struct trace_kprobe *tk;
@ -309,6 +311,8 @@ static struct trace_kprobe *alloc_trace_kprobe(const char *group,
else
tk->rp.kp.pre_handler = kprobe_dispatcher;
tk->rp.maxactive = maxactive;
if (!event || !is_good_name(event)) {
ret = -EINVAL;
goto error;
@ -598,8 +602,10 @@ static int create_trace_kprobe(int argc, char **argv)
{
/*
* Argument syntax:
* - Add kprobe: p[:[GRP/]EVENT] [MOD:]KSYM[+OFFS]|KADDR [FETCHARGS]
* - Add kretprobe: r[:[GRP/]EVENT] [MOD:]KSYM[+0] [FETCHARGS]
* - Add kprobe:
* p[:[GRP/]EVENT] [MOD:]KSYM[+OFFS]|KADDR [FETCHARGS]
* - Add kretprobe:
* r[MAXACTIVE][:[GRP/]EVENT] [MOD:]KSYM[+0] [FETCHARGS]
* Fetch args:
* $retval : fetch return value
* $stack : fetch stack address
@ -619,6 +625,7 @@ static int create_trace_kprobe(int argc, char **argv)
int i, ret = 0;
bool is_return = false, is_delete = false;
char *symbol = NULL, *event = NULL, *group = NULL;
int maxactive = 0;
char *arg;
unsigned long offset = 0;
void *addr = NULL;
@ -637,8 +644,28 @@ static int create_trace_kprobe(int argc, char **argv)
return -EINVAL;
}
if (argv[0][1] == ':') {
event = &argv[0][2];
event = strchr(&argv[0][1], ':');
if (event) {
event[0] = '\0';
event++;
}
if (is_return && isdigit(argv[0][1])) {
ret = kstrtouint(&argv[0][1], 0, &maxactive);
if (ret) {
pr_info("Failed to parse maxactive.\n");
return ret;
}
/* kretprobes instances are iterated over via a list. The
* maximum should stay reasonable.
*/
if (maxactive > KRETPROBE_MAXACTIVE_MAX) {
pr_info("Maxactive is too big (%d > %d).\n",
maxactive, KRETPROBE_MAXACTIVE_MAX);
return -E2BIG;
}
}
if (event) {
if (strchr(event, '/')) {
group = event;
event = strchr(group, '/') + 1;
@ -718,8 +745,8 @@ static int create_trace_kprobe(int argc, char **argv)
is_return ? 'r' : 'p', addr);
event = buf;
}
tk = alloc_trace_kprobe(group, event, addr, symbol, offset, argc,
is_return);
tk = alloc_trace_kprobe(group, event, addr, symbol, offset, maxactive,
argc, is_return);
if (IS_ERR(tk)) {
pr_info("Failed to allocate trace_probe.(%d)\n",
(int)PTR_ERR(tk));

39
tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_maxactive.tc 100644
View File

@ -0,0 +1,39 @@
#!/bin/sh
# description: Kretprobe dynamic event with maxactive
[ -f kprobe_events ] || exit_unsupported # this is configurable
echo > kprobe_events
# Test if we successfully reject unknown messages
if echo 'a:myprobeaccept inet_csk_accept' > kprobe_events; then false; else true; fi
# Test if we successfully reject too big maxactive
if echo 'r1000000:myprobeaccept inet_csk_accept' > kprobe_events; then false; else true; fi
# Test if we successfully reject unparsable numbers for maxactive
if echo 'r10fuzz:myprobeaccept inet_csk_accept' > kprobe_events; then false; else true; fi
# Test for kretprobe with event name without maxactive
echo 'r:myprobeaccept inet_csk_accept' > kprobe_events
grep myprobeaccept kprobe_events
test -d events/kprobes/myprobeaccept
echo '-:myprobeaccept' >> kprobe_events
# Test for kretprobe with event name with a small maxactive
echo 'r10:myprobeaccept inet_csk_accept' > kprobe_events
grep myprobeaccept kprobe_events
test -d events/kprobes/myprobeaccept
echo '-:myprobeaccept' >> kprobe_events
# Test for kretprobe without event name without maxactive
echo 'r inet_csk_accept' > kprobe_events
grep inet_csk_accept kprobe_events
echo > kprobe_events
# Test for kretprobe without event name with a small maxactive
echo 'r10 inet_csk_accept' > kprobe_events
grep inet_csk_accept kprobe_events
echo > kprobe_events
clear_trace