lkml.org 
[lkml]   [2017]   [Mar]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] tracing/kprobes: expose maxactive for kretprobe in kprobe_events
On Fri, 31 Mar 2017 10:08:39 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 31 Mar 2017 15:20:24 +0200
> Alban Crequy <alban.crequy@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 <alban@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.

default value is defined in Documentation/kprobes.txt sction 1.3.1, so
you'll just need to refer that.

Thank you,

>
> -- Steve
>
>
> >
> > FETCHARGS : Arguments. Each probe can have up to 128 args.
> > %REG : Fetch register REG


--
Masami Hiramatsu <mhiramat@kernel.org>

\
 
 \ /
  Last update: 2017-04-01 00:14    [W:0.049 / U:1.528 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site