ttyA has ld associated to n_gsm, when ttyA is closing, it triggers
to release gsmttyB's ld data dlci[B], then race would happen if gsmttyB
is opening in parallel.
Here are race cases we found recently in test:
CASE #1
====================================================================
releasing dlci[B] race with gsmtty_install(gsmttyB), then panic
in gsmtty_open(gsmttyB), as below:
tty_release(ttyA) tty_open(gsmttyB)
| |
----- gsmtty_install(gsmttyB)
| |
----- gsm_dlci_alloc(gsmttyB) => alloc dlci[B]
tty_ldisc_release(ttyA) -----
| |
gsm_dlci_release(dlci[B]) -----
| |
gsm_dlci_free(dlci[B]) -----
| |
----- gsmtty_open(gsmttyB)
gsmtty_open()
{
struct gsm_dlci *dlci = tty->driver_data; => here it uses dlci[B]
...
}
In gsmtty_open(gsmttyA), it uses dlci[B] which was release, so hit a panic.
=====================================================================
CASE #2
=====================================================================
releasing dlci[0] race with gsmtty_install(gsmttyB), then panic
in gsmtty_open(), as below:
tty_release(ttyA) tty_open(gsmttyB)
| |
----- gsmtty_install(gsmttyB)
| |
----- gsm_dlci_alloc(gsmttyB) => alloc dlci[B]
| |
----- gsmtty_open(gsmttyB) fail
| |
----- tty_release(gsmttyB)
| |
----- gsmtty_close(gsmttyB)
| |
----- gsmtty_detach_dlci(dlci[B])
| |
----- dlci_put(dlci[B])
| |
tty_ldisc_release(ttyA) -----
| |
gsm_dlci_release(dlci[0]) -----
| |
gsm_dlci_free(dlci[0]) -----
| |
----- dlci_put(dlci[0])
In gsmtty_detach_dlci(dlci[B]), it tries to use dlci[0] which was released,
then hit panic.
=====================================================================
IMHO, n_gsm tty operations would refer released ldisc, as long as
gsm_dlci_release() has chance to release ldisc data when some gsmtty operations
are not completed..
This patch is try to avoid it by:
1) in n_gsm driver, use a global gsm spin lock to avoid gsm_dlci_release() run in
parallel with gsmtty_install();
2) Increase dlci's ref count in gsmtty_install() instead of in gsmtty_open(), the
purpose is to prevent gsm_dlci_release() releasing dlci after gsmtty_install()
allocats dlci but before gsmtty_open increases dlci's ref count;
3) Decrease dlci's ref count in gsmtty_remove(), which is a tty framework api, and
this is the opposite process of step 2).
Signed-off-by: Chao Bi <chao.bi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
c284ee2cf1