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authorChao Bi <chao.bi@intel.com>2013-10-17 15:08:27 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-11-25 08:52:53 -0800
commitc284ee2cf12b55fa8496b2d098bf0938688f1c1c (patch)
tree5f553255c2b1dd33f6dcab7434ea2d7673bbb71b /drivers/tty/serial/lpc32xx_hs.c
parentf3014127ada32f51ce0baf0bee4c6324a601ef59 (diff)
n_gsm: race between ld close and gsmtty open
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>
Diffstat (limited to 'drivers/tty/serial/lpc32xx_hs.c')
0 files changed, 0 insertions, 0 deletions