Patch "dm: fix various targets to dm_register_target after module __init resources created" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

dm: fix various targets to dm_register_target after module __init resources created

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dm-fix-various-targets-to-dm_register_target-after-module-__init-resources-created.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "[email protected]" <[email protected]>
Date: Sat, 25 Nov 2017 01:43:50 +0800
Subject: dm: fix various targets to dm_register_target after module __init resources created

From: [email protected] <[email protected]>

commit 7e6358d244e4706fe612a77b9c36519a33600ac0 upstream.

A NULL pointer is seen if two concurrent "vgchange -ay -K <vg name>" processes race to load the dm-thin-pool module:

PID: 25992 TASK: ffff883cd7d23500 CPU: 4 COMMAND: "vgchange"
#0 [ffff883cd743d600] machine_kexec at ffffffff81038fa9 0000001 [ffff883cd743d660] crash_kexec at ffffffff810c5992 0000002 [ffff883cd743d730] oops_end at ffffffff81515c90 0000003 [ffff883cd743d760] no_context at ffffffff81049f1b 0000004 [ffff883cd743d7b0] __bad_area_nosemaphore at ffffffff8104a1a5 0000005 [ffff883cd743d800] bad_area at ffffffff8104a2ce 0000006 [ffff883cd743d830] __do_page_fault at ffffffff8104aa6f 0000007 [ffff883cd743d950] do_page_fault at ffffffff81517bae 0000008 [ffff883cd743d980] page_fault at ffffffff81514f95

     [exception RIP: kmem_cache_alloc+108]
     RIP: ffffffff8116ef3c RSP: ffff883cd743da38 RFLAGS: 00010046
     RAX: 0000000000000004 RBX: ffffffff81121b90 RCX: ffff881bf1e78cc0
     RDX: 0000000000000000 RSI: 00000000000000d0 RDI: 0000000000000000
     RBP: ffff883cd743da68 R8: ffff881bf1a4eb00 R9: 0000000080042000
     R10: 0000000000002000 R11: 0000000000000000 R12: 00000000000000d0
     R13: 0000000000000000 R14: 00000000000000d0 R15: 0000000000000246
     ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018

0000009 [ffff883cd743da70] mempool_alloc_slab at ffffffff81121ba5
0000010 [ffff883cd743da80] mempool_create_node at ffffffff81122083 0000011 [ffff883cd743dad0] mempool_create at ffffffff811220f4 0000012 [ffff883cd743dae0] pool_ctr at ffffffffa08de049 [dm_thin_pool] 0000013 [ffff883cd743dbd0] dm_table_add_target at ffffffffa0005f2f [dm_mod] 0000014 [ffff883cd743dc30] table_load at ffffffffa0008ba9 [dm_mod] 0000015 [ffff883cd743dc90] ctl_ioctl at ffffffffa0009dc4 [dm_mod]

The race results in a NULL pointer because:

Process A (vgchange -ay -K):
a. send DM_LIST_VERSIONS_CMD ioctl; b. pool_target not registered;
c. modprobe dm_thin_pool and wait until end.

Process B (vgchange -ay -K):
a. send DM_LIST_VERSIONS_CMD ioctl;
b. pool_target registered;
c. table_load->dm_table_add_target->pool_ctr; d. _new_mapping_cache is NULL and panic.
Note:
1. process A and process B are two concurrent processes.
2. pool_target can be detected by process B but _new_mapping_cache initialization has not ended.

To fix dm-thin-pool, and other targets (cache, multipath, and snapshot) with the same problem, simply dm_register_target() after all resources created during module init (as labelled with __init) are finished.

---
 drivers/md/dm-cache-target.c |   12 +++++-----
 drivers/md/dm-mpath.c        |   18 ++++++++--------
 drivers/md/dm-snap.c         |   48 +++++++++++++++++++++----------------------
 drivers/md/dm-thin.c         |   22 ++++++++-----------
 4 files changed, 49 insertions(+), 51 deletions(-)

@@ -3554,18 +3554,18 @@ static int __init dm_cache_init(void)
 {
 	int r;
 
-	r = dm_register_target(&cache_target);
-	if (r) {
-		DMERR("cache target registration failed: %d", r);
-		return r;
-	}
-
 	migration_cache = KMEM_CACHE(dm_cache_migration, 0);
 	if (!migration_cache) {
 		dm_unregister_target(&cache_target);
 		return -ENOMEM;
 	}
 
+	r = dm_register_target(&cache_target);
+	if (r) {
+		DMERR("cache target registration failed: %d", r);
+		return r;
+	}
+
 	return 0;
 }
 

@@ -1965,13 +1965,6 @@ static int __init dm_multipath_init(void
 {
 	int r;
 
-	r = dm_register_target(&multipath_target);
-	if (r < 0) {
-		DMERR("request-based register failed %d", r);
-		r = -EINVAL;
-		goto bad_register_target;
-	}
-
 	kmultipathd = alloc_workqueue("kmpathd", WQ_MEM_RECLAIM, 0);
 	if (!kmultipathd) {
 		DMERR("failed to create workqueue kmpathd");

@@ -1993,13 +1986,20 @@ static int __init dm_multipath_init(void
 		goto bad_alloc_kmpath_handlerd;
 	}
 
+	r = dm_register_target(&multipath_target);
+	if (r < 0) {
+		DMERR("request-based register failed %d", r);
+		r = -EINVAL;
+		goto bad_register_target;
+	}
+
 	return 0;
 
+bad_register_target:
+	destroy_workqueue(kmpath_handlerd);
 bad_alloc_kmpath_handlerd:
 	destroy_workqueue(kmultipathd);
 bad_alloc_kmultipathd:
-	dm_unregister_target(&multipath_target);
-bad_register_target:
 	return r;
 }
 

@@ -4355,30 +4355,28 @@ static struct target_type thin_target =
 
 static int __init dm_thin_init(void)
 {
-	int r;
+	int r = -ENOMEM;
 
 	pool_table_init();
 
+	_new_mapping_cache = KMEM_CACHE(dm_thin_new_mapping, 0);
+	if (!_new_mapping_cache)
+		return r;
+
 	r = dm_register_target(&thin_target);
 	if (r)
-		return r;
+		goto bad_new_mapping_cache;
 
 	r = dm_register_target(&pool_target);
 	if (r)
-		goto bad_pool_target;
-
-	r = -ENOMEM;
-
-	_new_mapping_cache = KMEM_CACHE(dm_thin_new_mapping, 0);
-	if (!_new_mapping_cache)
-		goto bad_new_mapping_cache;
+		goto bad_thin_target;
 
 	return 0;
 
-bad_new_mapping_cache:
-	dm_unregister_target(&pool_target);
-bad_pool_target:
+bad_thin_target:
 	dm_unregister_target(&thin_target);
+bad_new_mapping_cache:
+	kmem_cache_destroy(_new_mapping_cache);
 
 	return r;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/dm-fix-various-targets-to-dm_register_target-after-module-__init-resources-created.patch