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SubjectRe: [PATCH v2 tip/perf/core 1/6] perf symbols: find symbols in different mount namespace
Em Wed, Jul 05, 2017 at 06:48:08PM -0700, Krister Johansen escreveu:
> Teach perf how to resolve symbols from binaries that are in a different
> mount namespace from the tool. This allows perf to generate meaningful
> stack traces even if the binary resides in a different mount namespace
> from the tool.

I was trying to find a way to test after applying each of the patches in
this series, when it ocurred to me that if a process that appears on a
perf.data file has exit, how can we access /proc/%ITS_PID/something?

This can be used for synthesizing records at 'perf record' start, but
how to get that on a different machine, different arch, say?

We would use what is in PERF_RECORD_NAMESPACES? How?

What we have there is:

/*
* struct {
* struct perf_event_header header;
* u32 pid;
* u32 tid;
* u64 nr_namespaces;
* { u64 dev, inode; } [nr_namespaces];
* struct sample_id sample_id;
* };
*/
PERF_RECORD_NAMESPACES = 16,

So how would we use setns with that?

I must be missing something...

- Arnaldo

> Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
> ---
> tools/perf/util/dso.c | 1 +
> tools/perf/util/dso.h | 2 +
> tools/perf/util/map.c | 2 +
> tools/perf/util/namespaces.c | 127 +++++++++++++++++++++++++++++++++++++++++++
> tools/perf/util/namespaces.h | 33 +++++++++++
> tools/perf/util/symbol.c | 11 ++++
> tools/perf/util/thread.c | 3 +
> tools/perf/util/thread.h | 1 +
> 8 files changed, 180 insertions(+)
>
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 4e7ab61..beda40e 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -1236,6 +1236,7 @@ void dso__delete(struct dso *dso)
> dso_cache__free(dso);
> dso__free_a2l(dso);
> zfree(&dso->symsrc_filename);
> + nsinfo__zput(dso->nsinfo);
> pthread_mutex_destroy(&dso->lock);
> free(dso);
> }
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index bd061ba..78ec637 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -10,6 +10,7 @@
> #include <linux/types.h>
> #include <linux/bitops.h>
> #include "map.h"
> +#include "namespaces.h"
> #include "build-id.h"
>
> enum dso_binary_type {
> @@ -187,6 +188,7 @@ struct dso {
> void *priv;
> u64 db_id;
> };
> + struct nsinfo *nsinfo;
> refcount_t refcnt;
> char name[0];
> };
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index 2179b2d..5dc60ca 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -16,6 +16,7 @@
> #include "machine.h"
> #include <linux/string.h>
> #include "srcline.h"
> +#include "namespaces.h"
> #include "unwind.h"
>
> static void __maps__insert(struct maps *maps, struct map *map);
> @@ -200,6 +201,7 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
> if (type != MAP__FUNCTION)
> dso__set_loaded(dso, map->type);
> }
> + dso->nsinfo = nsinfo__get(thread->nsinfo);
> dso__put(dso);
> }
> return map;
> diff --git a/tools/perf/util/namespaces.c b/tools/perf/util/namespaces.c
> index 67dcbcc..bcc6bb1 100644
> --- a/tools/perf/util/namespaces.c
> +++ b/tools/perf/util/namespaces.c
> @@ -9,9 +9,13 @@
> #include "namespaces.h"
> #include "util.h"
> #include "event.h"
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <sched.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> +#include <unistd.h>
>
> struct namespaces *namespaces__new(struct namespaces_event *event)
> {
> @@ -35,3 +39,126 @@ void namespaces__free(struct namespaces *namespaces)
> {
> free(namespaces);
> }
> +
> +void nsinfo__init(struct nsinfo *nsi)
> +{
> + char oldns[PATH_MAX];
> + char *newns = NULL;
> + struct stat old_stat;
> + struct stat new_stat;
> +
> + if (snprintf(oldns, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
> + return;
> +
> + if (asprintf(&newns, "/proc/%d/ns/mnt", nsi->pid) == -1)
> + return;
> +
> + if (stat(oldns, &old_stat) < 0)
> + goto out;
> +
> + if (stat(newns, &new_stat) < 0)
> + goto out;
> +
> + /* Check if the mount namespaces differ, if so then indicate that we
> + * want to switch as part of looking up dso/map data.
> + */
> + if (old_stat.st_ino != new_stat.st_ino) {
> + nsi->need_setns = true;
> + nsi->mntns_path = newns;
> + newns = NULL;
> + }
> +
> +out:
> + free(newns);
> +}
> +
> +struct nsinfo *nsinfo__new(pid_t pid)
> +{
> + struct nsinfo *nsi = calloc(1, sizeof(*nsi));
> +
> + if (nsi != NULL) {
> + nsi->pid = pid;
> + nsi->need_setns = false;
> + nsinfo__init(nsi);
> + refcount_set(&nsi->refcnt, 1);
> + }
> +
> + return nsi;
> +}
> +
> +void nsinfo__delete(struct nsinfo *nsi)
> +{
> + zfree(&nsi->mntns_path);
> + free(nsi);
> +}
> +
> +struct nsinfo *nsinfo__get(struct nsinfo *nsi)
> +{
> + if (nsi)
> + refcount_inc(&nsi->refcnt);
> + return nsi;
> +}
> +
> +void nsinfo__put(struct nsinfo *nsi)
> +{
> + if (nsi && refcount_dec_and_test(&nsi->refcnt))
> + nsinfo__delete(nsi);
> +}
> +
> +void nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc)
> +{
> + char curpath[PATH_MAX];
> + int oldns = -1;
> + int newns = -1;
> +
> + if (nc == NULL)
> + return;
> +
> + nc->oldns = -1;
> + nc->newns = -1;
> +
> + if (!nsi || !nsi->need_setns)
> + return;
> +
> + if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
> + return;
> +
> + oldns = open(curpath, O_RDONLY);
> + if (oldns < 0)
> + return;
> +
> + newns = open(nsi->mntns_path, O_RDONLY);
> + if (newns < 0)
> + goto errout;
> +
> + if (setns(newns, CLONE_NEWNS) < 0)
> + goto errout;
> +
> + nc->oldns = oldns;
> + nc->newns = newns;
> + return;
> +
> +errout:
> + if (oldns > -1)
> + close(oldns);
> + if (newns > -1)
> + close(newns);
> +}
> +
> +void nsinfo__mountns_exit(struct nscookie *nc)
> +{
> + if (nc == NULL || nc->oldns == -1 || nc->newns == -1)
> + return;
> +
> + setns(nc->oldns, CLONE_NEWNS);
> +
> + if (nc->oldns > -1) {
> + close(nc->oldns);
> + nc->oldns = -1;
> + }
> +
> + if (nc->newns > -1) {
> + close(nc->newns);
> + nc->newns = -1;
> + }
> +}
> diff --git a/tools/perf/util/namespaces.h b/tools/perf/util/namespaces.h
> index 468f1e9..b20f6ea 100644
> --- a/tools/perf/util/namespaces.h
> +++ b/tools/perf/util/namespaces.h
> @@ -11,6 +11,7 @@
>
> #include "../perf.h"
> #include <linux/list.h>
> +#include <linux/refcount.h>
>
> struct namespaces_event;
>
> @@ -23,4 +24,36 @@ struct namespaces {
> struct namespaces *namespaces__new(struct namespaces_event *event);
> void namespaces__free(struct namespaces *namespaces);
>
> +struct nsinfo {
> + pid_t pid;
> + bool need_setns;
> + char *mntns_path;
> + refcount_t refcnt;
> +};
> +
> +struct nscookie {
> + int oldns;
> + int newns;
> +};
> +
> +void nsinfo__init(struct nsinfo *nsi);
> +struct nsinfo *nsinfo__new(pid_t pid);
> +void nsinfo__delete(struct nsinfo *nsi);
> +
> +struct nsinfo *nsinfo__get(struct nsinfo *nsi);
> +void nsinfo__put(struct nsinfo *nsi);
> +
> +void nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc);
> +void nsinfo__mountns_exit(struct nscookie *nc);
> +
> +static inline void __nsinfo__zput(struct nsinfo **nsip)
> +{
> + if (nsip) {
> + nsinfo__put(*nsip);
> + *nsip = NULL;
> + }
> +}
> +
> +#define nsinfo__zput(nsi) __nsinfo__zput(&nsi)
> +
> #endif /* __PERF_NAMESPACES_H */
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index e7a98db..60a9eaa 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -18,6 +18,8 @@
> #include "symbol.h"
> #include "strlist.h"
> #include "intlist.h"
> +#include "namespaces.h"
> +#include "vdso.h"
> #include "header.h"
> #include "path.h"
> #include "sane_ctype.h"
> @@ -1436,9 +1438,17 @@ int dso__load(struct dso *dso, struct map *map)
> struct symsrc *syms_ss = NULL, *runtime_ss = NULL;
> bool kmod;
> unsigned char build_id[BUILD_ID_SIZE];
> + struct nscookie nsc;
>
> + nsinfo__mountns_enter(dso->nsinfo, &nsc);
> pthread_mutex_lock(&dso->lock);
>
> + /* The vdso files always live in the host container, so don't go looking
> + * for them in the container's mount namespace.
> + */
> + if (dso__is_vdso(dso))
> + nsinfo__mountns_exit(&nsc);
> +
> /* check again under the dso->lock */
> if (dso__loaded(dso, map->type)) {
> ret = 1;
> @@ -1584,6 +1594,7 @@ int dso__load(struct dso *dso, struct map *map)
> out:
> dso__set_loaded(dso, map->type);
> pthread_mutex_unlock(&dso->lock);
> + nsinfo__mountns_exit(&nsc);
>
> return ret;
> }
> diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> index 378c418..aee9a42 100644
> --- a/tools/perf/util/thread.c
> +++ b/tools/perf/util/thread.c
> @@ -59,6 +59,8 @@ struct thread *thread__new(pid_t pid, pid_t tid)
> list_add(&comm->list, &thread->comm_list);
> refcount_set(&thread->refcnt, 1);
> RB_CLEAR_NODE(&thread->rb_node);
> + /* Thread holds first ref to nsdata. */
> + thread->nsinfo = nsinfo__new(pid);
> }
>
> return thread;
> @@ -91,6 +93,7 @@ void thread__delete(struct thread *thread)
> comm__free(comm);
> }
> unwind__finish_access(thread);
> + nsinfo__zput(thread->nsinfo);
>
> free(thread);
> }
> diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> index 4eb849e..cb1a5dd 100644
> --- a/tools/perf/util/thread.h
> +++ b/tools/perf/util/thread.h
> @@ -34,6 +34,7 @@ struct thread {
>
> void *priv;
> struct thread_stack *ts;
> + struct nsinfo *nsinfo;
> #ifdef HAVE_LIBUNWIND_SUPPORT
> void *addr_space;
> struct unwind_libunwind_ops *unwind_libunwind_ops;
> --
> 2.7.4

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