On Tue, 28 Mar 2017 15:52:22 +0200 Alban Crequy <alban.crequy@xxxxxxxxx> 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 I see, I found same issue last week... > > 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. Good! this is completely same what I'm planning to add. > > I need this for a bpf program attached to the kretprobe of > inet_csk_accept, which can sleep for a long time. I'm also preparing another patch for using kmalloc(GFP_ATOMIC) in kretprobe_pre_handler(), since this manual way is sometimes hard to estimate how many instances needed. Anyway, since that may involve unwilling memory allocation, this patch also needed. > > BugLink: https://github.com/iovisor/bcc/issues/1072 Could you also add Lukasz to Cc list, since he had reported an issue related this one. https://www.spinics.net/lists/linux-trace/msg00448.html Please see my comments below. > Signed-off-by: Alban Crequy <alban@xxxxxxxxxx> > --- > Documentation/trace/kprobetrace.txt | 4 +++- > kernel/trace/trace_kprobe.c | 34 +++++++++++++++++++++++++++++----- > 2 files changed, 32 insertions(+), 6 deletions(-) > > diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt > index 41ef9d8..655ca7e 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.(*) Here, yoy don't need (*), since [MAXACTIVE] is not a FETCHARGS. > > 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 5f688cc..807e01c 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -282,6 +282,7 @@ 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 +310,8 @@ 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 +601,10 @@ 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 +624,7 @@ 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 +643,26 @@ static int create_trace_kprobe(int argc, char **argv) > return -EINVAL; > } > > - if (argv[0][1] == ':') { > + if (is_return && isdigit(argv[0][1]) && strchr(&argv[0][1], ':')) { This only supports r[MAXACTIVE:[GRP/]EVENT]. e.g "r100" without event name. Thank you, > + event = strchr(&argv[0][1], ':') + 1; > + event[-1] = '\0'; > + 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 > 1024) { > + pr_info("Maxactive is too big.\n"); > + return -EINVAL; > + } > + } else if (argv[0][1] == ':') { > event = &argv[0][2]; > + } > + > + if (event) { > if (strchr(event, '/')) { > group = event; > event = strchr(group, '/') + 1; > @@ -718,8 +742,8 @@ 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)); > -- > 2.7.4 > -- Masami Hiramatsu <mhiramat@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
