[PATCH 3.16 054/254] dm: fix various targets to dm_register_target after module __init resources created

Ben Hutchings
2018-02-28T15:58:33Z

From: "monty_pavel@sina.com" <monty_pavel@sina.com>

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.

Signed-off-by: monty <monty_pavel@sina.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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(-)

--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -3108,18 +3108,18 @@ 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;
}

--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1688,13 +1688,6 @@ static int __init dm_multipath_init(void
if (!_mpio_cache)
return -ENOMEM;

- r = dm_register_target(&multipath_target);
- if (r < 0) {
- DMERR("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");
@@ -1716,17 +1709,24 @@ static int __init dm_multipath_init(void
goto bad_alloc_kmpath_handlerd;
}

+ r = dm_register_target(&multipath_target);
+ if (r < 0) {
+ DMERR("register failed %d", r);
+ r = -EINVAL;
+ goto bad_register_target;
+ }
+
DMINFO("version %u.%u.%u loaded",
multipath_target.version[0], multipath_target.version[1],
multipath_target.version[2]);

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:
kmem_cache_destroy(_mpio_cache);

return r;
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -2404,24 +2404,6 @@ static int __init dm_snapshot_init(void)
return r;
}

- r = dm_register_target(&snapshot_target);
- if (r < 0) {
- DMERR("snapshot target register failed %d", r);
- goto bad_register_snapshot_target;
- }
-
- r = dm_register_target(&origin_target);
- if (r < 0) {
- DMERR("Origin target register failed %d", r);
- goto bad_register_origin_target;
- }
-
- r = dm_register_target(&merge_target);
- if (r < 0) {
- DMERR("Merge target register failed %d", r);
- goto bad_register_merge_target;
- }
-
r = init_origin_hash();
if (r) {
DMERR("init_origin_hash failed.");
@@ -2442,19 +2424,37 @@ static int __init dm_snapshot_init(void)
goto bad_pending_cache;
}

+ r = dm_register_target(&snapshot_target);
+ if (r < 0) {
+ DMERR("snapshot target register failed %d", r);
+ goto bad_register_snapshot_target;
+ }
+
+ r = dm_register_target(&origin_target);
+ if (r < 0) {
+ DMERR("Origin target register failed %d", r);
+ goto bad_register_origin_target;
+ }
+
+ r = dm_register_target(&merge_target);
+ if (r < 0) {
+ DMERR("Merge target register failed %d", r);
+ goto bad_register_merge_target;
+ }
+
return 0;

-bad_pending_cache:
- kmem_cache_destroy(exception_cache);
-bad_exception_cache:
- exit_origin_hash();
-bad_origin_hash:
- dm_unregister_target(&merge_target);
bad_register_merge_target:
dm_unregister_target(&origin_target);
bad_register_origin_target:
dm_unregister_target(&snapshot_target);
bad_register_snapshot_target:
+ kmem_cache_destroy(pending_cache);
+bad_pending_cache:
+ kmem_cache_destroy(exception_cache);
+bad_exception_cache:
+ exit_origin_hash();
+bad_origin_hash:
dm_exception_store_exit();

return r;
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3521,30 +3521,28 @@ 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;
}