[CRIU] [PATCH] pages: Share page_ids between ns dump-helpers

[Dmitry Safonov]

After the commit 9d2e1dfebedf ("ipc: Keep shmem segments contents into
pagemap/page images"), SysV shmem pages are stored in the pages-<n>.img
files.  Where <n> is page_ids number.

The problem here is that we dump namespaces with a helper after fork().
This results in non-shared between child(s) and parent-criu counter
with the result of overwriting pages-*.img files later by helpers/criu.
This resulted in restore with corrupted shmem segments or
in the following failures on restore:
> (04.501019)      1: Error (criu/pagemap.c:265): Can't read mapping page 0: No such file or directory
> (04.637516)      1: Error (criu/pagemap.c:265): Can't read mapping page 0: No such file or directory

Allocate page_ids with shmalloc() and make it atomic.
As we need it in pre-dump, dump, page-server and rpc,
init it early in the main().

Cc: Pavel Emelyanov <xemul at virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov at virtuozzo.com>
---
 criu/crtools.c       |  3 +++
 criu/image.c         | 25 +++++++++++++++++++++----
 criu/include/image.h |  2 ++
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/criu/crtools.c b/criu/crtools.c
index b0f7b946cc56..a3dbbcb10668 100644
--- a/criu/crtools.c
+++ b/criu/crtools.c
@@ -325,6 +325,9 @@ int main(int argc, char *argv[], char *envp[])
 	if (fault_injection_init())
 		return 1;
 
+	if (images_init())
+		return 1;
+
 	cr_pb_init();
 	setproctitle_init(argc, argv, envp);
 
diff --git a/criu/image.c b/criu/image.c
index 62e8e7109e65..59b9dad5458d 100644
--- a/criu/image.c
+++ b/criu/image.c
@@ -17,6 +17,7 @@
 #include "images/inventory.pb-c.h"
 #include "images/pagemap.pb-c.h"
 #include "img-remote.h"
+#include "rst-malloc.h"
 
 bool ns_per_id = false;
 bool img_common_magic = true;
@@ -505,7 +506,23 @@ void close_image_dir(void)
 	close_service_fd(IMG_FD_OFF);
 }
 
-static unsigned long page_ids = 1;
+/*
+ * As we dump SysV shmem IPC into pages-<page_ids>.img,
+ * the keys should be shared in each dump ns-helpers and in criu.
+ */
+static atomic_t *page_ids;
+
+int images_init(void)
+{
+	page_ids = shmalloc(sizeof(*page_ids));
+	if (!page_ids) {
+		pr_err("Failed to shmalloc page_ids\n");
+		return -1;
+	}
+	atomic_set(page_ids, 1);
+
+	return 0;
+}
 
 void up_page_ids_base(void)
 {
@@ -517,8 +534,8 @@ void up_page_ids_base(void)
 	 * higher IDs.
 	 */
 
-	BUG_ON(page_ids != 1);
-	page_ids += 0x10000;
+	BUG_ON(atomic_read(page_ids) != 1);
+	atomic_add(0x10000, page_ids);
 }
 
 struct cr_img *open_pages_image_at(int dfd, unsigned long flags, struct cr_img *pmi, u32 *id)
@@ -531,7 +548,7 @@ struct cr_img *open_pages_image_at(int dfd, unsigned long flags, struct cr_img *
 		pagemap_head__free_unpacked(h, NULL);
 	} else {
 		PagemapHead h = PAGEMAP_HEAD__INIT;
-		*id = h.pages_id = page_ids++;
+		*id = h.pages_id = atomic_inc_return(page_ids);
 		if (pb_write_one(pmi, &h, PB_PAGEMAP_HEAD) < 0)
 			return NULL;
 	}
diff --git a/criu/include/image.h b/criu/include/image.h
index d9c4bdbc8da4..60e44297a858 100644
--- a/criu/include/image.h
+++ b/criu/include/image.h
@@ -170,4 +170,6 @@ extern int read_img_str(struct cr_img *, char **pstr, int size);
 
 extern void close_image(struct cr_img *);
 
+extern int images_init(void);
+
 #endif /* __CR_IMAGE_H__ */
-- 
2.13.1