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authorHou Tao <houtao1@huawei.com>2017-11-01 15:42:36 +0800
committerMike Snitzer <snitzer@redhat.com>2017-11-10 15:44:56 -0500
commitb9a41d21dceadf8104812626ef85dc56ee8a60ed (patch)
tree29d6c8b92379abcf9a78af22379cbac2ec3d37b1
parent856eb0916d181da6d043cc33e03f54d5c5bbe54a (diff)
dm: fix race between dm_get_from_kobject() and __dm_destroy()
The following BUG_ON was hit when testing repeat creation and removal of DM devices: kernel BUG at drivers/md/dm.c:2919! CPU: 7 PID: 750 Comm: systemd-udevd Not tainted 4.1.44 Call Trace: [<ffffffff81649e8b>] dm_get_from_kobject+0x34/0x3a [<ffffffff81650ef1>] dm_attr_show+0x2b/0x5e [<ffffffff817b46d1>] ? mutex_lock+0x26/0x44 [<ffffffff811df7f5>] sysfs_kf_seq_show+0x83/0xcf [<ffffffff811de257>] kernfs_seq_show+0x23/0x25 [<ffffffff81199118>] seq_read+0x16f/0x325 [<ffffffff811de994>] kernfs_fop_read+0x3a/0x13f [<ffffffff8117b625>] __vfs_read+0x26/0x9d [<ffffffff8130eb59>] ? security_file_permission+0x3c/0x44 [<ffffffff8117bdb8>] ? rw_verify_area+0x83/0xd9 [<ffffffff8117be9d>] vfs_read+0x8f/0xcf [<ffffffff81193e34>] ? __fdget_pos+0x12/0x41 [<ffffffff8117c686>] SyS_read+0x4b/0x76 [<ffffffff817b606e>] system_call_fastpath+0x12/0x71 The bug can be easily triggered, if an extra delay (e.g. 10ms) is added between the test of DMF_FREEING & DMF_DELETING and dm_get() in dm_get_from_kobject(). To fix it, we need to ensure the test of DMF_FREEING & DMF_DELETING and dm_get() are done in an atomic way, so _minor_lock is used. The other callers of dm_get() have also been checked to be OK: some callers invoke dm_get() under _minor_lock, some callers invoke it under _hash_lock, and dm_start_request() invoke it after increasing md->open_count. Cc: stable@vger.kernel.org Signed-off-by: Hou Tao <houtao1@huawei.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
-rw-r--r--drivers/md/dm.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index adb874c2411b..dcfa1a8c9390 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2711,11 +2711,15 @@ struct mapped_device *dm_get_from_kobject(struct kobject *kobj)
md = container_of(kobj, struct mapped_device, kobj_holder.kobj);
- if (test_bit(DMF_FREEING, &md->flags) ||
- dm_deleting_md(md))
- return NULL;
-
+ spin_lock(&_minor_lock);
+ if (test_bit(DMF_FREEING, &md->flags) || dm_deleting_md(md)) {
+ md = NULL;
+ goto out;
+ }
dm_get(md);
+out:
+ spin_unlock(&_minor_lock);
+
return md;
}