[CRIU] [PATCH 3/5] epoll: Drop duped and closed targets

[Cyrill Gorcunov]

Due to kernel epoll engine specifics we may have a case
where some target file are present in fdinfo twice and
only one local file descriptor is present: an easy
reproduction is to dup fd, add it into epoll and
close it then.

Thus for such case we resolve all targets but then
run validation procedure that every target is unique.

Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
---
 criu/eventpoll.c       | 83 ++++++++++++++++++++++++++++++++++++++----
 images/eventpoll.proto |  2 +
 2 files changed, 77 insertions(+), 8 deletions(-)

diff --git a/criu/eventpoll.c b/criu/eventpoll.c
index 40ecd398e89a..21879165d1a4 100644
--- a/criu/eventpoll.c
+++ b/criu/eventpoll.c
@@ -122,13 +122,32 @@ static void dequeue_dinfo(struct eventpoll_dinfo *dinfo)
 	xfree(dinfo);
 }
 
+static int etfd_cmp(const void *__a, const void *__b)
+{
+	EventpollTfdEntry *a = (EventpollTfdEntry *)__a;
+	EventpollTfdEntry *b = (EventpollTfdEntry *)__b;
+
+	if (a->tfd > b->tfd)
+		return 1;
+	if (a->tfd < b->tfd)
+		return -1;
+	if (a->pid < b->pid)
+		return 1;
+	if (a->pid > b->pid)
+		return -1;
+	return 0;
+}
+
 int flush_eventpoll_dinfo_queue(void)
 {
 	struct eventpoll_dinfo *dinfo, *tmp;
-	ssize_t i;
+	size_t i, j;
 
 	list_for_each_entry_safe(dinfo, tmp, &dinfo_list, list) {
 		EventpollFileEntry *e = dinfo->e;
+		EventpollTfdEntry *tfde_copy = NULL;
+		size_t n_tfd_copy = e->n_tfd;
+		int ret;
 
 		for (i = 0; i < e->n_tfd; i++) {
 			EventpollTfdEntry *tfde = e->tfd[i];
@@ -154,22 +173,70 @@ int flush_eventpoll_dinfo_queue(void)
 			pr_debug("kid_lookup_epoll: rbsearch match pid %d efd %d tfd %d toff %u -> %d\n",
 				 dinfo->pid, dinfo->efd, tfde->tfd, dinfo->toff[i].off, t->idx);
 
-			/* Make sure the pid matches */
+			/*
+			 * If PIDs are mismatched it means the target file is
+			 * came from another process (either by SCM or via
+			 * inheritance: epoll inhereted but new targed in child
+			 * opened and added).
+			 */
 			if (t->pid != dinfo->pid) {
-				pr_debug("kid_lookup_epoll: pid mismatch %d %d efd %d tfd %d toff %u\n",
-					 dinfo->pid, t->pid, dinfo->efd, tfde->tfd, dinfo->toff[i].off);
+				pr_err("kid_lookup_epoll: pid mismatch %d %d efd %d tfd %d toff %u\n",
+				       dinfo->pid, t->pid, dinfo->efd, tfde->tfd, dinfo->toff[i].off);
+				tfde->has_pid = true;
+				tfde->pid = t->pid;
 				goto err;
 			}
 
 			tfde->tfd = t->idx;
 		}
 
+		/*
+		 * Once we've resolved all targets we should drop those
+		 * which are in state of dup/add/close (epoll kernel engine
+		 * saves all records while the target may simply not exist).
+		 *
+		 * tfd:        4 events:       1d data: ...
+		 * tfd:      704 events:       1d data: ...
+		 *
+		 * Here an application added fd=4 to an epoll, then dup'ed
+		 * fd=4 to fd=704, added it to the epoll and then closed fd=704.
+		 * Thus after resolve we will have two tf=4 records in
+		 * the queue.
+		 */
+		if (e->n_tfd) {
+			qsort(e->tfd, e->n_tfd, sizeof(e->tfd[0]), etfd_cmp);
+			tfde_copy = xmemdup(e->tfd, sizeof(e->tfd[0]) * n_tfd_copy);
+			if (!tfde_copy) {
+				pr_err("kid_lookup_epoll: Can't allocate copy of tfds\n");
+				goto err;
+			}
+
+			for (j = i = 1; i < n_tfd_copy; i++) {
+				if (!etfd_cmp(e->tfd[i], e->tfd[i-1])) {
+					pr_debug("kid_lookup_epoll: id %#x same tfd %u pid %d\n",
+						 e->id, e->tfd[i]->pid, e->tfd[i]->tfd);
+					continue;
+				}
+				e->tfd[j++] = e->tfd[i];
+			}
+			e->n_tfd = j;
+		}
+
 		pr_info_eventpoll("Dumping ", e);
-		if (pb_write_one(img_from_set(glob_imgset, CR_FD_FILES), dinfo->fe, PB_FILE))
-			goto err;
+		ret = pb_write_one(img_from_set(glob_imgset, CR_FD_FILES), dinfo->fe, PB_FILE);
+		if (!ret) {
+			for (i = 0; i < e->n_tfd; i++)
+				pr_info_eventpoll_tfd("Dumping: ", e->id, e->tfd[i]);
+		}
 
-		for (i = 0; i < e->n_tfd; i++)
-			pr_info_eventpoll_tfd("Dumping: ", e->id, e->tfd[i]);
+		if (tfde_copy) {
+			memcpy(e->tfd, tfde_copy, sizeof(e->tfd[0]) * n_tfd_copy);
+			e->n_tfd = n_tfd_copy;
+			xfree(tfde_copy);
+		}
+
+		if (ret)
+			goto err;
 
 		dequeue_dinfo(dinfo);
 	}
diff --git a/images/eventpoll.proto b/images/eventpoll.proto
index 4a8d1b834ef8..24909c695398 100644
--- a/images/eventpoll.proto
+++ b/images/eventpoll.proto
@@ -12,6 +12,8 @@ message eventpoll_tfd_entry {
 	optional uint32		dev	= 5;
 	optional uint64		inode	= 6;
 	optional uint64		pos	= 7;
+	/* to find foreigner targets */
+	optional uint32		pid	= 8;
 }
 
 message eventpoll_file_entry {
-- 
2.17.2