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perf tools: Restore proper cwd on return from mnt namespace

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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: 843ff37bb5 ("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>
This commit is contained in:
Jiri Olsa 2018-11-01 18:00:01 +01:00 committed by Arnaldo Carvalho de Melo
parent 8feb8efef9
commit b01c1f69c8
2 changed files with 16 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
tools/perf/util/namespaces.c
View File

@ -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;

1
tools/perf/util/namespaces.h
View File

@ -38,6 +38,7 @@ struct nsinfo {
struct nscookie {
int oldns;
int newns;
char *oldcwd;
};
int nsinfo__init(struct nsinfo *nsi);