On Mon, 3 Apr 2017 12:36:22 +0200 Alban Crequy <alban.cre...@gmail.com> wrote:
> From: Alban Crequy <al...@kinvolk.io> > > 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 > Signed-off-by: Alban Crequy <al...@kinvolk.io> Looks good to me. Acked-by: Masami Hiramatsu <mhira...@kernel.org> Thanks! > > --- > > Changes since v2: > - Explain the default maxactive value in the documentation. > (Review from Steven Rostedt) > > Changes since v1: > - Remove "(*)" from documentation. (Review from Masami Hiramatsu) > - Fix support for "r100" without the event name (Review from Masami Hiramatsu) > - Get rid of magic numbers within the code. (Review from Steven Rostedt) > Note that I didn't use KRETPROBE_MAXACTIVE_ALLOC since that patch is not > merged. > - Return -E2BIG when maxactive is too big. > - Add basic selftest > --- > Documentation/trace/kprobetrace.txt | 5 ++- > kernel/trace/trace_kprobe.c | 39 > ++++++++++++++++++---- > .../ftrace/test.d/kprobe/kretprobe_maxactive.tc | 39 > ++++++++++++++++++++++ > 3 files changed, 76 insertions(+), 7 deletions(-) > create mode 100644 > tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_maxactive.tc > > diff --git a/Documentation/trace/kprobetrace.txt > b/Documentation/trace/kprobetrace.txt > index 41ef9d8..25f3960 100644 > --- a/Documentation/trace/kprobetrace.txt > +++ b/Documentation/trace/kprobetrace.txt > @@ -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 > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index c5089c7..ae81f3c 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -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)); > diff --git > a/tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_maxactive.tc > b/tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_maxactive.tc > new file mode 100644 > index 0000000..57abdf1 > --- /dev/null > +++ b/tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_maxactive.tc > @@ -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 > -- > 2.7.4 > -- Masami Hiramatsu <mhira...@kernel.org> -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
