criu: Dump and restore pdeath_sig value

The implementation is pretty straightforward. When dumping per-thread
misc data with parasite, collect one, then write in thread_core_info.

On restore wait for creds restore and put the value back (some creds
changes drop it to zero).
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

cr-dump.c

@@ -689,6 +689,10 @@ int dump_thread_core(int pid, CoreEntry *core, const struct parasite_dump_thread
 		CORE_THREAD_ARCH_INFO(core)->clear_tid_addr = encode_pointer(ti->tid_addr);
 		BUG_ON(!tc->sas);
 		copy_sas(tc->sas, &ti->sas);
+		if (ti->pdeath_sig) {
+			tc->has_pdeath_sig = true;
+			tc->pdeath_sig = ti->pdeath_sig;
+		}
 	}
 
 	return ret;

cr-restore.c

@@ -2557,6 +2557,11 @@ static int sigreturn_restore(pid_t pid, CoreEntry *core)
 			thread_args[i].has_futex	= true;
 			thread_args[i].futex_rla	= tcore->thread_core->futex_rla;
 			thread_args[i].futex_rla_len	= tcore->thread_core->futex_rla_len;
+			thread_args[i].pdeath_sig	= tcore->thread_core->pdeath_sig;
+			if (tcore->thread_core->pdeath_sig > _KNSIG) {
+				pr_err("Pdeath signal is too big\n");
+				goto err;
+			}
 
 			ret = prep_sched_info(&thread_args[i].sp, tcore->thread_core);
 			if (ret)

include/parasite.h

@@ -141,6 +141,7 @@ struct parasite_dump_thread {
 	pid_t			tid;
 	tls_t			tls;
 	stack_t			sas;
+	int			pdeath_sig;
 };
 
 /*

include/restorer.h

@@ -90,6 +90,7 @@ struct thread_restore_args {
 
 	siginfo_t			*siginfo;
 	unsigned int			siginfo_nr;
+	int				pdeath_sig;
 } __aligned(64);
 
 struct task_restore_args {

pie/parasite.c

@@ -35,6 +35,10 @@ static struct parasite_dump_pages_args *mprotect_args = NULL;
 #define SPLICE_F_GIFT	0x08
 #endif
 
+#ifndef PR_GET_PDEATHSIG
+#define PR_GET_PDEATHSIG  2
+#endif
+
 static int mprotect_vmas(struct parasite_dump_pages_args *args)
 {
 	struct parasite_vma_entry *vmas, *vma;
@@ -145,9 +149,15 @@ static int dump_thread_common(struct parasite_dump_thread *ti)
 
 	arch_get_tls(&ti->tls);
 	ret = sys_prctl(PR_GET_TID_ADDRESS, (unsigned long) &ti->tid_addr, 0, 0, 0);
-	if (ret == 0)
-		ret = sys_sigaltstack(NULL, &ti->sas);
+	if (ret)
+		goto out;
 
+	ret = sys_sigaltstack(NULL, &ti->sas);
+	if (ret)
+		goto out;
+
+	ret = sys_prctl(PR_GET_PDEATHSIG, (unsigned long)&ti->pdeath_sig, 0, 0, 0);
+out:
 	return ret;
 }
 

pie/restorer.c

@@ -35,6 +35,10 @@
 
 #include "asm/restorer.h"
 
+#ifndef PR_SET_PDEATHSIG
+#define PR_SET_PDEATHSIG 1
+#endif
+
 #define sys_prctl_safe(opcode, val1, val2, val3)			\
 	({								\
 		long __ret = sys_prctl(opcode, val1, val2, val3, 0);	\
@@ -189,6 +193,20 @@ static int restore_creds(CredsEntry *ce)
 	return 0;
 }
 
+/*
+ * This should be done after creds restore, as
+ * some creds changes might drop the value back
+ * to zero.
+ */
+
+static inline int restore_pdeath_sig(struct thread_restore_args *ta)
+{
+	if (ta->pdeath_sig)
+		return sys_prctl(PR_SET_PDEATHSIG, ta->pdeath_sig, 0, 0, 0);
+	else
+		return 0;
+}
+
 static int restore_dumpable_flag(MmEntry *mme)
 {
 	int current_dumpable;
@@ -349,6 +367,7 @@ long __export_restore_thread(struct thread_restore_args *args)
 		goto core_restore_end;
 
 	restore_finish_stage(CR_STATE_RESTORE_SIGCHLD);
+	restore_pdeath_sig(args);
 	restore_finish_stage(CR_STATE_RESTORE_CREDS);
 	futex_dec_and_wake(&thread_inprogress);
 
@@ -1004,6 +1023,7 @@ long __export_restore_task(struct task_restore_args *args)
 
 	ret = restore_creds(&args->creds);
 	ret = ret || restore_dumpable_flag(&args->mm);
+	ret = ret || restore_pdeath_sig(args->t);
 
 	futex_set_and_wake(&thread_inprogress, args->nr_threads);
 

protobuf/core.proto

@@ -48,6 +48,7 @@ message thread_core_entry {
 	optional uint32			sched_prio	= 5;
 	optional uint64			blk_sigset	= 6;
 	optional thread_sas_entry	sas		= 7;
+	optional uint32			pdeath_sig	= 8;
 }
 
 message task_rlimits_entry {