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restore: Split restore_one_helper() and wait exiting zombie children

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Zombie is also can be choosen as a parent for task helper like
any other task.

If the task helper exits between restore_finish_stage(CR_STATE_RESTORE)
and zombie_prepare_signals()->SIG_UNBLOCK, the standard criu SIGCHLD
handler is called, and the restore fails:

(00.057762)     41: Error (criu/cr-restore.c:1557): 40 exited, status=0
(00.057815) Error (criu/cr-restore.c:2465): Restoring FAILED.

This patch makes restore_one_zombie() behave as restore_one_helper()
and to wait children exits before allowing SIGCHLD. This makes us
safe against races with exiting children.

See next patch for test details.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
This commit is contained in:
Kirill Tkhai
2017-12-28 13:50:54 +03:00
committed by Andrei Vagin
parent ec761499e5
commit e23806f3d0
1 changed files with 20 additions and 13 deletions
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33
criu/cr-restore.c
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@@ -957,6 +957,8 @@ static int wait_on_helpers_zombies(void)
return 0;
}
static int wait_exiting_children(void);
static int restore_one_zombie(CoreEntry *core)
{
int exit_code = core->tc->exit_code;
@@ -975,7 +977,7 @@ static int restore_one_zombie(CoreEntry *core)
prctl(PR_SET_NAME, (long)(void *)core->tc->comm, 0, 0, 0);
if (task_entries != NULL) {
restore_finish_stage(task_entries, CR_STATE_RESTORE);
wait_exiting_children();
zombie_prepare_signals();
}
@@ -1079,21 +1081,10 @@ static bool child_death_expected(void)
return false;
}
/*
* Restore a helper process - artificially created by criu
* to restore attributes of process tree.
* - sessions for each leaders are dead
* - process groups with dead leaders
* - dead tasks for which /proc/<pid>/... is opened by restoring task
* - whatnot
*/
static int restore_one_helper(void)
static int wait_exiting_children(void)
{
siginfo_t info;
if (prepare_fds(current))
return -1;
if (!child_death_expected()) {
/*
* Restoree has no children that should die, during restore,
@@ -1136,6 +1127,22 @@ static int restore_one_helper(void)
return 0;
}
/*
* Restore a helper process - artificially created by criu
* to restore attributes of process tree.
* - sessions for each leaders are dead
* - process groups with dead leaders
* - dead tasks for which /proc/<pid>/... is opened by restoring task
* - whatnot
*/
static int restore_one_helper(void)
{
if (prepare_fds(current))
return -1;
return wait_exiting_children();
}
static int restore_one_task(int pid, CoreEntry *core)
{
int i, ret;