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Commit b01c1f69 authored by Jiri Olsa's avatar Jiri Olsa Committed by Arnaldo Carvalho de Melo
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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: default avatarJiri 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: 843ff37b ("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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 8feb8efe

tools/perf/util/namespaces.c

+15 −2
Original line number Diff line number Diff line
@@ -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 @@ void nsinfo__mountns_enter(struct nsinfo *nsi, 


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;

tools/perf/util/namespaces.h

+1 −0
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ struct nsinfo { 
struct nscookie {

	int			oldns;

	int			newns;

	char			*oldcwd;

};



int nsinfo__init(struct nsinfo *nsi);