Messages in this thread Patch in this message |  | | Date | Tue, 17 Feb 2015 16:06:09 -0500 | From | Aristeu Rozanski <> | Subject | [PATCH] n_tty_read: check for hanging tty while waiting for input |
| |
If the console has a canonical reader and the respective tty hangs up, it'll waste a wake up and will never release the last ldisc reference so the hangup process can finish:
n_tty_read(): (..) add_wait_queue(&tty->read_wait, &wait); while (nr) { (..) if (!input_available_p(tty, 0)) { if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) { up_read(&tty->termios_rwsem); tty_flush_to_ldisc(tty); down_read(&tty->termios_rwsem); if (!input_available_p(tty, 0)) { retval = -EIO; break; } } else { -> if (tty_hung_up_p(file)) break; this won't work because file->f_op never gets set to &hung_up_tty_fops: __tty_hangup():
spin_lock(&tty_files_lock); /* This breaks for file handles being sent over AF_UNIX sockets ? */ list_for_each_entry(priv, &tty->tty_files, list) { filp = priv->file; if (filp->f_op->write == redirected_tty_write) cons_filp = filp; -> if (filp->f_op->write != tty_write) -> continue; closecount++; __tty_fasync(-1, filp, 0); /* can't block */ -> filp->f_op = &hung_up_tty_fops; } spin_unlock(&tty_files_lock);
refs = tty_signal_session_leader(tty, exit_session); /* Account for the p->signal references we killed */ while (refs--) tty_kref_put(tty);
/* * it drops BTM and thus races with reopen * we protect the race by TTY_HUPPING */ -> tty_ldisc_hangup(tty);
So while the canonical read waits for input, it'll sleep, be awaken by tty_ldisc_hangup() and then immediately going back to sleep without dropping the reference to the ldisc gained on tty_read(). This isn't noticiable in a non canonical read due that it'll eventually timeout.
The proposed patch checks for TTY_HUPPING flag in order to leave if there's no input.
This is easily reproduced by opening /dev/console (my test case was a virtual machine with serial console), setting as canonical and waiting on a read(). Then, in another session, killing agetty that is running on ttyS0 which will issue a hangup.
[ 240.439045] INFO: task (agetty):1323 blocked for more than 120 seconds. [ 240.439569] Not tainted 3.13.0-rc3+ #11 [ 240.439972] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 240.440596] (agetty) D ffff88007fd94440 0 1323 1 0x00000080 [ 240.441253] ffff88007bca1c50 0000000000000086 ffff88007989b0c0 0000000000014440 [ 240.441857] ffff88007bca1fd8 0000000000014440 ffff88007989b0c0 ffff88007989b0c0 [ 240.442561] ffff88007ad46c30 7fffffffffffffff 0000000000000001 ffff88007ad46c28 [ 240.443296] Call Trace: [ 240.443506] [<ffffffff815c8c99>] schedule+0x29/0x70 [ 240.443883] [<ffffffff815c7f59>] schedule_timeout+0x209/0x2d0 [ 240.444395] [<ffffffff810974b5>] ? check_preempt_curr+0x85/0xa0 [ 240.444850] [<ffffffff810974e9>] ? ttwu_do_wakeup+0x19/0xd0 [ 240.445343] [<ffffffff8109764d>] ? ttwu_do_activate.constprop.80+0x5d/0x70 [ 240.445868] [<ffffffff810995eb>] ? try_to_wake_up+0xeb/0x2b0 [ 240.446363] [<ffffffff815cbdaa>] ldsem_down_write+0xda/0x227 [ 240.446797] [<ffffffff81099822>] ? default_wake_function+0x12/0x20 [ 240.447359] [<ffffffff815cc43d>] tty_ldisc_lock_pair_timeout+0x7d/0x100 [ 240.447861] [<ffffffff8136e519>] tty_ldisc_hangup+0xc9/0x220 [ 240.448355] [<ffffffff81365463>] __tty_hangup+0x363/0x4b0 [ 240.448768] [<ffffffff81367cc5>] tty_ioctl+0x865/0xbb0 [ 240.449219] [<ffffffff811bb52a>] ? do_filp_open+0x3a/0x90 [ 240.449634] [<ffffffff811bd900>] do_vfs_ioctl+0x2e0/0x4c0 [ 240.450066] [<ffffffff8124ea76>] ? file_has_perm+0x86/0xa0 [ 240.450543] [<ffffffff811bdb61>] SyS_ioctl+0x81/0xa0 [ 240.450921] [<ffffffff815d4b69>] system_call_fastpath+0x16/0x1b
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Aristeu Rozanski <aris@redhat.com>
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 0f74945..4fb909d 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -2189,6 +2189,8 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, } else { if (tty_hung_up_p(file)) break; + if (test_bit(TTY_HUPPING, &tty->flags)) + break; if (!timeout) break; if (file->f_flags & O_NONBLOCK) {
|  |