On Fri, 31 Mar 2017 15:20:24 +0200 Alban Crequy <alban.cre...@gmail.com> wrote:
> 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> > > --- > > 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 | 4 ++- > kernel/trace/trace_kprobe.c | 39 > ++++++++++++++++++---- > .../ftrace/test.d/kprobe/kretprobe_maxactive.tc | 39 > ++++++++++++++++++++++ > 3 files changed, 75 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..7051a20 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 +32,8 @@ 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. BTW, to me, 0 means none (no instances can probe). This should have a better description of what "0" actually means. -- Steve > > FETCHARGS : Arguments. Each probe can have up to 128 args. > %REG : Fetch register REG
