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Subject[patch 042/100] dm: path selector use module refcount directly
-stable review patch.  If anyone has any objections, please let us know.
---------------------

From: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>

upstream commit: aea9058801c0acfa2831af1714da412dfb0018c2

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

Cc: stable@kernel.org
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
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
@@ -17,9 +17,7 @@

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)
@@ -45,12 +43,8 @@ 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;
@@ -84,11 +78,7 @@ 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);
}
@@ -136,11 +126,6 @@ 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);


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