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Date: Wed, 5 Jul 2017 13:44:52 -0700
From: Krister Johansen <kjlx@...pleofstupid.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Krister Johansen <kjlx@...pleofstupid.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH tip/perf/core 1/7] perf symbols: find symbols in
different mount namespace
On Mon, Jul 03, 2017 at 03:38:27PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Jun 30, 2017 at 07:18:53PM -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.
>
> Clear implementation overall, followed tools/perf/ coding style, uses
> reference counts, etc, great! some comments below
Thanks! Appreciate the review comments.
> > Signed-off-by: Krister Johansen <kjlx@...pleofstupid.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..d7f31e0 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)
> > +{
> > + free(nsi->mntns_path);
>
> zfree(&nsi->mntns_path);
Thanks; will fix.
> > + 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;
> > +
> > + (void) setns(nc->oldns, CLONE_NEWNS);
>
> We haven't been using (void) in these cases, is this to silence warnings
> about not checking the return of functions? Is this one with some
> attribute for that? But you're using even in simpler things like
> close()...
>
> Also if we have multiple threads using this interface, wouldn't there be
> races? Humm, from 'man setns()':
>
> Given a file descriptor referring to a namespace, reassociate the calling thread with that namespace.
>
> Ok, so should be ok.
Sorry, this is a leftover, still in my fingers, from when I had to
contend with code going through clint all the time. I'll remove the
leading void casts.
The setns() call operates on a per-task basis, so it should okay.
> > +
> > + if (nc->oldns > -1) {
> > + (void) close(nc->oldns);
> > + nc->oldns = -1;
> > + }
> > +
> > + if (nc->newns > -1) {
> > + (void) 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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