Commit c2239788 authored Nov 12, 2018 by Chanho Min Committed by Rafael J. Wysocki Nov 19, 2018

exec: make de_thread() freezable



Suspend fails due to the exec family of functions blocking the freezer.
The casue is that de_thread() sleeps in TASK_UNINTERRUPTIBLE waiting for
all sub-threads to die, and we have the deadlock if one of them is frozen.
This also can occur with the schedule() waiting for the group thread leader
to exit if it is frozen.

In our machine, it causes freeze timeout as bellows.

Freezing of tasks failed after 20.010 seconds (1 tasks refusing to freeze, wq_busy=0):
setcpushares-ls D ffffffc00008ed70     0  5817   1483 0x0040000d
 Call trace:
[<ffffffc00008ed70>] __switch_to+0x88/0xa0
[<ffffffc000d1c30c>] __schedule+0x1bc/0x720
[<ffffffc000d1ca90>] schedule+0x40/0xa8
[<ffffffc0001cd784>] flush_old_exec+0xdc/0x640
[<ffffffc000220360>] load_elf_binary+0x2a8/0x1090
[<ffffffc0001ccff4>] search_binary_handler+0x9c/0x240
[<ffffffc00021c584>] load_script+0x20c/0x228
[<ffffffc0001ccff4>] search_binary_handler+0x9c/0x240
[<ffffffc0001ce8e0>] do_execveat_common.isra.14+0x4f8/0x6e8
[<ffffffc0001cedd0>] compat_SyS_execve+0x38/0x48
[<ffffffc00008de30>] el0_svc_naked+0x24/0x28

To fix this, make de_thread() freezable. It looks safe and works fine.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Chanho Min <chanho.min@lge.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

parent 9ff01193

fs/exec.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -62,6 +62,7 @@
		#include <linux/oom.h>
		#include <linux/compat.h>
		#include <linux/vmalloc.h>
		#include <linux/freezer.h>

		#include <linux/uaccess.h>
		#include <asm/mmu_context.h>
		@@ -1083,7 +1084,7 @@ static int de_thread(struct task_struct *tsk)
		while (sig->notify_count) {
		__set_current_state(TASK_KILLABLE);
		spin_unlock_irq(lock);
		schedule();
		freezable_schedule();
		if (unlikely(__fatal_signal_pending(tsk)))
		goto killed;
		spin_lock_irq(lock);
		@@ -1111,7 +1112,7 @@ static int de_thread(struct task_struct *tsk)
		__set_current_state(TASK_KILLABLE);
		write_unlock_irq(&tasklist_lock);
		cgroup_threadgroup_change_end(tsk);
		schedule();
		freezable_schedule();
		if (unlikely(__fatal_signal_pending(tsk)))
		goto killed;
		}

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