Imported linux-2.6.27.39 suse/xen patches.

[ipfire-2.x.git] / src / patches / suse-2.6.27.39 / patches.fixes / dm-path-selector-ref-count

diff --git a/src/patches/suse-2.6.27.39/patches.fixes/dm-path-selector-ref-count b/src/patches/suse-2.6.27.39/patches.fixes/dm-path-selector-ref-count
new file mode 100644 (file)
index 0000000..8696401
--- /dev/null
+++ b/src/patches/suse-2.6.27.39/patches.fixes/dm-path-selector-ref-count
@@ -0,0 +1,124 @@
+From: "Jun'ichi Nomura" <j-nomura@ce.jp.nec.com>
+Subject: dm-path-selector: fix refcount corruption
+
+Hi,
+
+Refcounting of path-selector module is not safe in SMP environment.
+The counter may corrupt and trigger BUG() like this:
+  kernel BUG at linux-2.6.29-rc3/drivers/md/dm-path-selector.c:90!
+though it's rare under normal usage.
+
+The bug is here:
+  void dm_put_path_selector(struct path_selector_type *pst)
+  {
+  ...
+        down_read(&_ps_lock);
+        psi = __find_path_selector_type(pst->name);
+        if (!psi)
+                goto out;
+
+        if (--psi->use == 0)
+                module_put(psi->pst.module);
+
+        BUG_ON(psi->use < 0);
+
+The code manipulates the counter without exclusive lock or atomic ops.
+So if 2 processors come in, the counter may corrupt.
+
+While it could be fixed using atomic ops for the counter manipulation,
+we can just drop the 'use' counter like Cheng Renquan did for dm-target:
+https://www.redhat.com/archives/dm-devel/2008-December/msg00075.html
+
+(Actually, without his patch, dm-target.c hits the same problem.)
+
+Signed-off-by: Hannes Reinecke <hare@suse.de>
+
+-- 
+Jun'ichi Nomura, NEC Corporation
+
+
+Fix refcount corruption in dm-path-selector
+
+Refcounting with non-atomic ops under shared lock will corrupt the counter
+in multi-processor system and may trigger BUG_ON().
+Use module refcount.
+# same approach as dm-target-use-module-refcount-directly.patch here
+# https://www.redhat.com/archives/dm-devel/2008-December/msg00075.html
+
+Typical oops:
+  kernel BUG at linux-2.6.29-rc3/drivers/md/dm-path-selector.c:90!
+  Pid: 11148, comm: dmsetup Not tainted 2.6.29-rc3-nm #1
+  dm_put_path_selector+0x4d/0x61 [dm_multipath]
+  Call Trace:
+   [<ffffffffa031d3f9>] free_priority_group+0x33/0xb3 [dm_multipath]
+   [<ffffffffa031d4aa>] free_multipath+0x31/0x67 [dm_multipath]
+   [<ffffffffa031d50d>] multipath_dtr+0x2d/0x32 [dm_multipath]
+   [<ffffffffa015d6c2>] dm_table_destroy+0x64/0xd8 [dm_mod]
+   [<ffffffffa015b73a>] __unbind+0x46/0x4b [dm_mod]
+   [<ffffffffa015b79f>] dm_swap_table+0x60/0x14d [dm_mod]
+   [<ffffffffa015f963>] dev_suspend+0xfd/0x177 [dm_mod]
+   [<ffffffffa0160250>] dm_ctl_ioctl+0x24c/0x29c [dm_mod]
+   [<ffffffff80288cd3>] ? get_page_from_freelist+0x49c/0x61d
+   [<ffffffffa015f866>] ? dev_suspend+0x0/0x177 [dm_mod]
+   [<ffffffff802bf05c>] vfs_ioctl+0x2a/0x77
+   [<ffffffff802bf4f1>] do_vfs_ioctl+0x448/0x4a0
+   [<ffffffff802bf5a0>] sys_ioctl+0x57/0x7a
+   [<ffffffff8020c05b>] system_call_fastpath+0x16/0x1b
+
+Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
+---
+ drivers/md/dm-path-selector.c |   21 +++------------------
+ 1 file changed, 3 insertions(+), 18 deletions(-)
+
+--- a/drivers/md/dm-path-selector.c
++++ b/drivers/md/dm-path-selector.c
+@@ -16,9 +16,7 @@
+ 
+ struct ps_internal {
+       struct path_selector_type pst;
+-
+       struct list_head list;
+-      long use;
+ };
+ 
+ #define pst_to_psi(__pst) container_of((__pst), struct ps_internal, pst)
+@@ -44,12 +42,8 @@ static struct ps_internal *get_path_sele
+ 
+       down_read(&_ps_lock);
+       psi = __find_path_selector_type(name);
+-      if (psi) {
+-              if ((psi->use == 0) && !try_module_get(psi->pst.module))
+-                      psi = NULL;
+-              else
+-                      psi->use++;
+-      }
++      if (psi && !try_module_get(psi->pst.module))
++              psi = NULL;
+       up_read(&_ps_lock);
+ 
+       return psi;
+@@ -83,11 +77,7 @@ void dm_put_path_selector(struct path_se
+       if (!psi)
+               goto out;
+ 
+-      if (--psi->use == 0)
+-              module_put(psi->pst.module);
+-
+-      BUG_ON(psi->use < 0);
+-
++      module_put(psi->pst.module);
+ out:
+       up_read(&_ps_lock);
+ }
+@@ -135,11 +125,6 @@ int dm_unregister_path_selector(struct p
+               return -EINVAL;
+       }
+ 
+-      if (psi->use) {
+-              up_write(&_ps_lock);
+-              return -ETXTBSY;
+-      }
+-
+       list_del(&psi->list);
+ 
+       up_write(&_ps_lock);