perf tools: Restore proper cwd on return from mnt namespace

When reporting on 'record' server we try to retrieve/use the mnt
namespace of the profiled tasks. We use following API with cookie to
hold the return namespace, roughly:

  nsinfo__mountns_enter(struct nsinfo *nsi, struct nscookie *nc)
    setns(newns, 0);
  ...
  new ns related open..
  ...
  nsinfo__mountns_exit(struct nscookie *nc)
    setns(nc->oldns)

Once finished we setns to old namespace, which also sets the current
working directory (cwd) to "/", trashing the cwd we had.

This is mostly fine, because we use absolute paths almost everywhere,
but it screws up 'perf diff':

  # perf diff
  failed to open perf.data: No such file or directory  (try 'perf record' first)
  ...

Adding the current working directory to be part of the cookie and
restoring it in the nsinfo__mountns_exit call.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Krister Johansen <kjlx@templeofstupid.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: 843ff37bb59e ("perf symbols: Find symbols in different mount namespace")
Link: http://lkml.kernel.org/r/20181101170001.30019-1-jolsa@kernel.org
[ No need to check for NULL args for free(), use zfree() for struct members ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/namespaces.c b/tools/perf/util/namespaces.c
index cf8bd123cf73fb017cde3d60c7b912743847b965..aed170bd4384ef72a012453a578497bfe912ae61 100644 (file)
--- a/tools/perf/util/namespaces.c
+++ b/tools/perf/util/namespaces.c
@@ -18,6 +18,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
+#include <asm/bug.h>
 
 struct namespaces *namespaces__new(struct namespaces_event *event)
 {
@@ -186,6 +187,7 @@ void nsinfo__mountns_enter(struct nsinfo *nsi,
        char curpath[PATH_MAX];
        int oldns = -1;
        int newns = -1;
+       char *oldcwd = NULL;
 
        if (nc == NULL)
                return;
@@ -199,9 +201,13 @@ void nsinfo__mountns_enter(struct nsinfo *nsi,
        if (snprintf(curpath, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
                return;
 
+       oldcwd = get_current_dir_name();
+       if (!oldcwd)
+               return;
+
        oldns = open(curpath, O_RDONLY);
        if (oldns < 0)
-               return;
+               goto errout;
 
        newns = open(nsi->mntns_path, O_RDONLY);
        if (newns < 0)
@@ -210,11 +216,13 @@ void nsinfo__mountns_enter(struct nsinfo *nsi,
        if (setns(newns, CLONE_NEWNS) < 0)
                goto errout;
 
+       nc->oldcwd = oldcwd;
        nc->oldns = oldns;
        nc->newns = newns;
        return;
 
 errout:
+       free(oldcwd);
        if (oldns > -1)
                close(oldns);
        if (newns > -1)
@@ -223,11 +231,16 @@ errout:
 
 void nsinfo__mountns_exit(struct nscookie *nc)
 {
-       if (nc == NULL || nc->oldns == -1 || nc->newns == -1)
+       if (nc == NULL || nc->oldns == -1 || nc->newns == -1 || !nc->oldcwd)
                return;
 
        setns(nc->oldns, CLONE_NEWNS);
 
+       if (nc->oldcwd) {
+               WARN_ON_ONCE(chdir(nc->oldcwd));
+               zfree(&nc->oldcwd);
+       }
+
        if (nc->oldns > -1) {
                close(nc->oldns);
                nc->oldns = -1;

diff --git a/tools/perf/util/namespaces.h b/tools/perf/util/namespaces.h
index cae1a9a397222ca4b06a17f5bda0d4aa6774ce5d..d5f46c09ea31922fb46f59158ab9e05138aed1b1 100644 (file)
--- a/tools/perf/util/namespaces.h
+++ b/tools/perf/util/namespaces.h
@@ -38,6 +38,7 @@ struct nsinfo {
 struct nscookie {
        int                     oldns;
        int                     newns;
+       char                    *oldcwd;
 };
 
 int nsinfo__init(struct nsinfo *nsi);