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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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