net/9p/client.c: put refcount of trans_mod in error case in parse_opts()

[ Upstream commit c290fba8c4ce6530cd941ea14db5a4ac2f77183f ]

In my testing, the second mount will fail after umounting successfully.
The reason is that we put refcount of trans_mod in the correct case
rather than the error case in parse_opts() at last.  That will cause the
refcount decrease to -1, and when we try to get trans_mod again in
try_module_get(), we could only increase refcount to 0 which will cause
failure as follows:

parse_opts
  v9fs_get_trans_by_name
    try_module_get : return NULL to caller which cause error

So we should put refcount of trans_mod in error case.

Link: http://lkml.kernel.org/r/5B3F39A0.2030509@huawei.com
Fixes: 9421c3e64137ec ("net/9p/client.c: fix potential refcnt problem of trans module")
Signed-off-by: Jun Piao <piaojun@huawei.com>
Reviewed-by: Yiwen Jiang <jiangyiwen@huawei.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Dominique Martinet <dominique.martinet@cea.fr>
Tested-by: Dominique Martinet <dominique.martinet@cea.fr>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/9p/client.c b/net/9p/client.c
index 21e6df1cc70f407a85e486d2e26ec7254a6d399b..0ad6993aaa9b5ee1e7bb27379bc6985fb8dfeecb 100644 (file)
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -228,7 +228,8 @@ static int parse_opts(char *opts, struct p9_client *clnt)
        }
 
 free_and_return:
-       v9fs_put_trans(clnt->trans_mod);
+       if (ret)
+               v9fs_put_trans(clnt->trans_mod);
        kfree(tmp_options);
        return ret;
 }