Messages in this thread |  | | Date | 3 Feb 2013 20:03:03 -0500 | From | "George Spelvin" <> | Subject | 3.8-rc regression with pps-ldisc due to 70ece7a731 |
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"TTY: n_tty, add ldisc data to n_tty"
The PPS line discipline has incestuous relations with the n_tty line discipline, using some hooks to call internal routines.
However, I started noticing violent kernel explosions when testing 3.8-rc, and after a bit of digging, I think it's due to the fact that the PPS code assumes that the ->ldisc pointer is available to hold a pointer to a "pps" structure, but this commit started using it in the core n_tty discipline.
If you look at pps_tty_open in drivers/pps/clients/pps-ldisc.c, you can see it does:
pps = pps_register_source(&info, PPS_CAPTUREBOTH | \ PPS_OFFSETASSERT | PPS_OFFSETCLEAR); if (pps == NULL) { pr_err("cannot register PPS source \"%s\"\n", info.path); return -ENOMEM; } tty->disc_data = pps;
/* Should open N_TTY ldisc too */ ret = alias_n_tty_open(tty);
Where "alias_n_tty_open" is filled in by n_tty_inherit_ops() to be n_tty_open(). However, in this commit, n_tty_open() now allocates its own structure and overwrites the disc_data pointer, leading to an earth-shattering kaboom as NULL pointers are dereferenced in interrupt handlers.
My first thought is to reserve a pointer in n_tty_data for the pps structure and update the pps code to chase pointers one more level. But I wanted to solicit opinions.
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