From: Andrey Ryabinin <aryabi...@virtuozzo.com>
So, the ptrace() hangs if we try to attach to stopped task
from freezing cgroup:
Tracee: Tracer:
static bool do_signal_stop(int signr)
__set_current_state(TASK_STOPPED);
freezable_schedule();
freezer_do_not_count();
schedule(); /* waiting for wake up */
ptrace_attach()
if
(task_is_stopped(task) &&
task_set_jobctl_pending(task,
JOBCTL_TRAP_STOP | JOBCTL_TRAPPING))
signal_wake_up_state(task, __TASK_STOPPED);
/* woken up by ptrace_attach() */
freezer_count();
__refrigerator()
/* And here we will
hang, because tracee
* is now frozen in
__refrigerator() */
wait_on_bit(&task->jobctl, JOBCTL_TRAPPING_BIT,
TASK_UNINTERRUPTIBLE);
The right fix for this would be to rework cgroup freezer,
but for now, we could workaround this by forbiding to freeze task
if JOBCTL_TRAPPING_BIT is set.
ptrace_attach() is the only place which sets that bit iff
task_is_stopped(), thus TRAPPING_BIT is clear indication that ptrace_attach
waits for clearing that bit => we shouldn't freeze.
https://jira.sw.ru/browse/PSBM-40683
Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
Acked-by: Andrew Vagin <ava...@virtuozzo.com>
(cherry picked from vz8 commit b91869099308cf0551819443d81b0f910382da2c)
Signed-off-by: Andrey Zhadchenko <andrey.zhadche...@virtuozzo.com>
---
kernel/freezer.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/freezer.c b/kernel/freezer.c
index 45ab36f..1ed34ea 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -42,6 +42,9 @@ bool freezing_slow_path(struct task_struct *p)
if (test_tsk_thread_flag(p, TIF_MEMDIE))
return false;
+ if (p->jobctl & JOBCTL_TRAPPING)
+ return false;
+
if (pm_nosig_freezing || cgroup_freezing(p))
return true;
--
1.8.3.1
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