[CRIU] [PATCH 09/10] restore: Add restoration of alternative signal stack, v2

[Cyrill Gorcunov]

On Tue, Jul 09, 2013 at 08:52:11PM +0400, Pavel Emelyanov wrote:
> > 
> > setup_sas does check that ->sas is not null, thus in protobuf
> > format it's either valid pointer to sas data or NULL otherwise.
> 
> OK. Let's assume we ptraced a task with SAS and injected a parasite
> into it. Later for any reason the sigreturn rescue code started to
> return from parasite. Would we restore it with proper SAS?

Yes, as far as I know. The sas saving code is generic, iow

+static void copy_sas(ThreadSasEntry *dst, stack_t *src)
+{
+	dst->ss_sp = encode_pointer(src->ss_sp);
+	dst->ss_size = (u64)src->ss_size;
+	dst->ss_flags = src->ss_flags;
+}
+
+static int parasite_init(struct parasite_ctl *ctl, pid_t pid, struct pstree_item *item)
 {
 	static int ssock = -1;
 
@@ -421,6 +428,9 @@ static int parasite_init(struct parasite_ctl *ctl, pid_t pid, int nr_threads)
 	ctl->sig_blocked = args->sig_blocked;
 	ctl->use_sig_blocked = true;
 
+	BUG_ON(!item->core[0]->thread_core->sas);
+	copy_sas(item->core[0]->thread_core->sas, &args->sas);
+

on init we save dumpee sas in memory, thus if something go wrong we restore
it via sigreturn by parasite code.