Re: [PATCH v3] perf inject --jit: Remove //anon mmap events

[Jiri Olsa]

On Thu, Oct 31, 2019 at 01:30:36PM -0700, Steve MacLean wrote:
> From: Steve MacLean <Steve.MacLean@xxxxxxxxxxxxx>
> 
> While a JIT is jitting code it will eventually need to commit more pages and
> change these pages to executable permissions.
> 
> Typically the JIT will want these colocated to minimize branch displacements.
> 
> The kernel will coalesce these anonymous mapping with identical permissions
> before sending an MMAP event for the new pages. This means the mmap event for
> the new pages will include the older pages.
> 
> These anonymous mmap events will obscure the jitdump injected pseudo events.
> This means that the jitdump generated symbols, machine code, debugging info,
> and unwind info will no longer be used.
> 
> Observations:
> 
> When a process emits a jit dump marker and a jitdump file, the perf-xxx.map
> file represents inferior information which has been superceded by the
> jitdump jit-xxx.dump file.
> 
> Further the '//anon*' mmap events are only required for the legacy
> perf-xxx.map mapping.
> 
> When attaching to an existing process, the synthetic anon map events are
> given a time stamp of -1. These should not obscure the jitdump events which
> have an actual time.
> 
> Summary:
> 
> Use thread->priv to store whether a jitdump file has been processed
> 
> During "perf inject --jit", discard "//anon*" mmap events for any pid which
> has sucessfully processed a jitdump file.
> 
> Committer testing:
> 
> // jitdump case
> perf record <app with jitdump>
> perf inject --jit --input perf.data --output perfjit.data
> 
> // verify mmap "//anon" events present initially
> perf script --input perf.data --show-mmap-events | grep '//anon'
> // verify mmap "//anon" events removed
> perf script --input perfjit.data --show-mmap-events | grep '//anon'
> 
> // no jitdump case
> perf record <app without jitdump>
> perf inject --jit --input perf.data --output perfjit.data
> 
> // verify mmap "//anon" events present initially
> perf script --input perf.data --show-mmap-events | grep '//anon'
> // verify mmap "//anon" events not removed
> perf script --input perfjit.data --show-mmap-events | grep '//anon'
> 
> Repro:
> 
> This issue was discovered while testing the initial CoreCLR jitdump
> implementation. https://github.com/dotnet/coreclr/pull/26897.
> 

Stephane,
are you ok with this fix?

thanks,
jirka

> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Steve MacLean <Steve.MacLean@xxxxxxxxxxxxx>
> ---
>  tools/perf/builtin-inject.c |  4 ++--
>  tools/perf/util/jitdump.c   | 31 ++++++++++++++++++++++++++++++-
>  2 files changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index 372ecb3..0f38862 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/tools/perf/builtin-inject.c
> @@ -263,7 +263,7 @@ static int perf_event__jit_repipe_mmap(struct perf_tool *tool,
>  	 * if jit marker, then inject jit mmaps and generate ELF images
>  	 */
>  	ret = jit_process(inject->session, &inject->output, machine,
> -			  event->mmap.filename, sample->pid, &n);
> +			  event->mmap.filename, event->mmap.pid, &n);
>  	if (ret < 0)
>  		return ret;
>  	if (ret) {
> @@ -301,7 +301,7 @@ static int perf_event__jit_repipe_mmap2(struct perf_tool *tool,
>  	 * if jit marker, then inject jit mmaps and generate ELF images
>  	 */
>  	ret = jit_process(inject->session, &inject->output, machine,
> -			  event->mmap2.filename, sample->pid, &n);
> +			  event->mmap2.filename, event->mmap2.pid, &n);
>  	if (ret < 0)
>  		return ret;
>  	if (ret) {
> diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
> index e3ccb0c..d18596e 100644
> --- a/tools/perf/util/jitdump.c
> +++ b/tools/perf/util/jitdump.c
> @@ -26,6 +26,7 @@
>  #include "jit.h"
>  #include "jitdump.h"
>  #include "genelf.h"
> +#include "thread.h"
>  
>  #include <linux/ctype.h>
>  #include <linux/zalloc.h>
> @@ -749,6 +750,28 @@ static int jit_repipe_debug_info(struct jit_buf_desc *jd, union jr_entry *jr)
>  	return 0;
>  }
>  
> +static void jit_add_pid(struct machine *machine, pid_t pid)
> +{
> +	struct thread *thread = machine__findnew_thread(machine, pid, pid);
> +
> +	if (!thread) {
> +		pr_err("%s: thread %d not found or created\n", __func__, pid);
> +		return;
> +	}
> +
> +	thread->priv = (void *)1;
> +}
> +
> +static bool jit_has_pid(struct machine *machine, pid_t pid)
> +{
> +	struct thread *thread = machine__find_thread(machine, pid, pid);
> +
> +	if (!thread)
> +		return 0;
> +
> +	return (bool)thread->priv;
> +}
> +
>  int
>  jit_process(struct perf_session *session,
>  	    struct perf_data *output,
> @@ -764,8 +787,13 @@ static int jit_repipe_debug_info(struct jit_buf_desc *jd, union jr_entry *jr)
>  	/*
>  	 * first, detect marker mmap (i.e., the jitdump mmap)
>  	 */
> -	if (jit_detect(filename, pid))
> +	if (jit_detect(filename, pid)) {
> +		// Strip //anon* mmaps if we processed a jitdump for this pid
> +		if (jit_has_pid(machine, pid) && (strncmp(filename, "//anon", 6) == 0))
> +			return 1;
> +
>  		return 0;
> +	}
>  
>  	memset(&jd, 0, sizeof(jd));
>  
> @@ -784,6 +812,7 @@ static int jit_repipe_debug_info(struct jit_buf_desc *jd, union jr_entry *jr)
>  
>  	ret = jit_inject(&jd, filename);
>  	if (!ret) {
> +		jit_add_pid(machine, pid);
>  		*nbytes = jd.bytes_written;
>  		ret = 1;
>  	}
> -- 
> 1.8.3.1
>