Messages in this thread | | | Date | Wed, 17 May 2017 15:44:56 +0200 | From | Sascha Hauer <> | Subject | tty: closing n_gsm line discipline always times out |
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Hi All,
When the n_gsm line discipline is closed it wants to shutdown the line discipline properly and asks the link partner to end the mux protocol. This is done in gsm_cleanup_mux() around line 2050 in n_gsm.c:
if (dlci) { gc = gsm_control_send(gsm, CMD_CLD, NULL, 0); if (gc) gsm_control_wait(gsm, gc); }
The call stack is like this:
(struct tty_ldisc_ops).close -> gsmld_close -> gsmld_detach_gsm -> gsm_cleanup_mux
(struct tty_ldisc_ops).close is called at tty_release time or when the line discipline is changed. At tty_release time the tty is already shutdown, so we cannot send anything anymore. In this case our link partner never closes the mux protocol, which means we can never re-open it again. When instead the line discipline is changed back to N_TTY to close the protocol, gsm_control_send works fine, but the tty_ldisc is locked and thus the chars received by the UART never make it to the line discipline and gsm_control_wait times out.
There's obviously something wrong here. Any ideas how to fix that? When we are not allowed to send/receive at tty_release time, do we need a new n_gsm specific ioctl to shutdown the mux?
Sascha
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