From b258d645463205dfec79a8fcc10bc77a77bd53f3 Mon Sep 17 00:00:00 2001
From: Ahmed Elaidy <elaidya225@gmail.com>
Date: Tue, 3 Mar 2026 00:18:14 +0200
Subject: [PATCH] criu: restore timer_slack_ns per thread

During restore, set the per-thread timer_slack_ns value via
PR_SET_TIMERSLACK if the image contains it. This completes the
checkpoint/restore cycle for the timer slack property.

The restore is skipped for images that do not contain the field,
maintaining backward compatibility with older image formats.

Signed-off-by: Ahmed Elaidy <elaidya225@gmail.com>
---
 criu/cr-restore.c       |  5 +++++
 criu/include/restorer.h |  2 ++
 criu/pie/restorer.c     | 22 ++++++++++++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/criu/cr-restore.c b/criu/cr-restore.c
index 957478ce2..4e7bd5e79 100644
--- a/criu/cr-restore.c
+++ b/criu/cr-restore.c
@@ -3466,6 +3466,11 @@ static int sigreturn_restore(pid_t pid, struct task_restore_args *task_args, uns
 			goto err;
 		}
 
+		if (tcore->thread_core->has_timerslack_ns) {
+			thread_args[i].has_timerslack_ns = true;
+			thread_args[i].timerslack_ns = tcore->thread_core->timerslack_ns;
+		}
+
 		ret = prep_sched_info(&thread_args[i].sp, tcore->thread_core);
 		if (ret)
 			goto err;
diff --git a/criu/include/restorer.h b/criu/include/restorer.h
index 78da19182..5a141664c 100644
--- a/criu/include/restorer.h
+++ b/criu/include/restorer.h
@@ -114,6 +114,8 @@ struct thread_restore_args {
 	unsigned int siginfo_n;
 
 	int pdeath_sig;
+	bool has_timerslack_ns;
+	unsigned long timerslack_ns;
 
 	struct thread_creds_args *creds_args;
 
diff --git a/criu/pie/restorer.c b/criu/pie/restorer.c
index 694a5e874..ee7b2c994 100644
--- a/criu/pie/restorer.c
+++ b/criu/pie/restorer.c
@@ -66,6 +66,10 @@
 #define PR_SET_PDEATHSIG 1
 #endif
 
+#ifndef PR_SET_TIMERSLACK
+#define PR_SET_TIMERSLACK 29
+#endif
+
 #ifndef PR_SET_CHILD_SUBREAPER
 #define PR_SET_CHILD_SUBREAPER 36
 #endif
@@ -417,6 +421,22 @@ static inline int restore_pdeath_sig(struct thread_restore_args *ta)
 	return 0;
 }
 
+static inline int restore_timerslack(struct thread_restore_args *ta)
+{
+	int ret;
+
+	if (!ta->has_timerslack_ns)
+		return 0;
+
+	ret = sys_prctl(PR_SET_TIMERSLACK, ta->timerslack_ns, 0, 0, 0);
+	if (ret) {
+		pr_err("Unable to set PR_SET_TIMERSLACK(%lu): %d\n", ta->timerslack_ns, ret);
+		return -1;
+	}
+
+	return 0;
+}
+
 static int restore_dumpable_flag(MmEntry *mme)
 {
 	int current_dumpable;
@@ -830,6 +850,7 @@ __visible long __export_restore_thread(struct thread_restore_args *args)
 	ret = restore_creds(args->creds_args, args->ta->proc_fd, args->ta->lsm_type, args->ta->uid);
 	ret = ret || restore_dumpable_flag(&args->ta->mm);
 	ret = ret || restore_pdeath_sig(args);
+	ret = ret || restore_timerslack(args);
 	if (ret)
 		BUG();
 
@@ -2303,6 +2324,7 @@ __visible long __export_restore_task(struct task_restore_args *args)
 	ret = restore_creds(args->t->creds_args, args->proc_fd, args->lsm_type, args->uid);
 	ret = ret || restore_dumpable_flag(&args->mm);
 	ret = ret || restore_pdeath_sig(args->t);
+	ret = ret || restore_timerslack(args->t);
 	ret = ret || restore_child_subreaper(args->child_subreaper);
 
 	atomic_set(&thread_inprogress, args->nr_threads);