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SubjectRe: flush_to_ldisc accesses tty after free (was: [PATCH 21/21] TTY: move tty buffers to tty_port)
On 01.12.2012 18:59, Peter Hurley wrote:
> (cc'ing Ilya Zykov <ilya@ilyx.ru> because the test jig below is based on
> his test program from https://lkml.org/lkml/2012/11/29/368 -- just want
> to give credit where credit is due)
>
> On Fri, 2012-11-30 at 18:52 -0500, Sasha Levin wrote:
>>
>> Still reproducible, I'm still seeing this with the patch above applied:
>>
>> [ 1315.419759] ------------[ cut here ]------------
>> [ 1315.420611] WARNING: at drivers/tty/tty_buffer.c:476 flush_to_ldisc+0x60/0x200()
>> [ 1315.423098] tty is NULL
>
> Thanks for sticking with this Sasha. Finally me too.
>
> ---
> [ 88.331234] WARNING: at /home/peter/src/kernels/next/drivers/tty/tty_buffer.c:435 flush_to_ldisc+0x194/0x1d0()
> [ 88.334505] Hardware name: Bochs
> [ 88.335618] tty is bad=-1
> [ 88.335703] Modules linked in: netconsole configfs bnep rfcomm bluetooth snd_hda_intel snd_hda_codec snd_hwdep
> parport_pc ppdev snd_pcm snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq snd_timer snd_seq_device mac_hid
> psmouse snd i2c_piix4 soundcore snd_page_alloc microcode serio_raw virtio_balloon lp parport floppy 8139too 8139cp
> [ 88.345272] Pid: 39, comm: kworker/1:1 Tainted: G W 3.7.0-next-20121129+ttydebug-xeon #20121129+ttydebug
> [ 88.347736] Call Trace:
> [ 88.349024] [<ffffffff81058aff>] warn_slowpath_common+0x7f/0xc0
> [ 88.350383] [<ffffffff81058bf6>] warn_slowpath_fmt+0x46/0x50
> [ 88.351745] [<ffffffff81432bd4>] flush_to_ldisc+0x194/0x1d0
> [ 88.353047] [<ffffffff816f7fe1>] ? _raw_spin_unlock_irq+0x21/0x50
> [ 88.354190] [<ffffffff8108a809>] ? finish_task_switch+0x49/0xe0
> [ 88.355436] [<ffffffff81077ad1>] process_one_work+0x121/0x490
> [ 88.357674] [<ffffffff81432a40>] ? __tty_buffer_flush+0x90/0x90
> [ 88.358954] [<ffffffff81078c84>] worker_thread+0x164/0x3e0
> [ 88.360247] [<ffffffff81078b20>] ? manage_workers+0x120/0x120
> [ 88.361282] [<ffffffff8107e230>] kthread+0xc0/0xd0
> [ 88.362284] [<ffffffff816f0000>] ? cmos_do_probe+0x2eb/0x3bf
> [ 88.363391] [<ffffffff8107e170>] ? flush_kthread_worker+0xb0/0xb0
> [ 88.364797] [<ffffffff816fff6c>] ret_from_fork+0x7c/0xb0
> [ 88.366087] [<ffffffff8107e170>] ? flush_kthread_worker+0xb0/0xb0
> [ 88.367266] ---[ end trace 453a7c9f38fbfec0 ]---
>
>
> I figured out how to make this reproduce easily. The test jig at the end
> of this email will generate this multiple times a second.
>
> The test creates a pty pair and spawns a child which writes to the slave
> pts, while the parent waits for the first write and then abruptly closes
> the master ptm and kills the child. (Just in case, I'd only run the jig
> in a disposable vm. Obviously, the vm needs multiple cores and extra pty
> serial devices ;)
>
>>From instrumenting the tty_release() path, it's clear that tty_buffer
> work is still scheduled even after tty_release_ldisc() has run. For
> example, with this patch I get the warning below it.
>
> [Further analysis to follow in subsequent mail...]
>
> --- >% ---
> [PATCH -next] tty: WARN if buffer work racing with tty free
>
>
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
> ---
> drivers/tty/tty_io.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 1ce50ec..9d53aec 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1511,6 +1511,8 @@ static void queue_release_one_tty(struct kref *kref)
> {
> struct tty_struct *tty = container_of(kref, struct tty_struct, kref);
>
> + WARN_ON(work_pending(&tty->port->buf.work));
> +
> /* The hangup queue is now free so we can reuse it rather than
> waste a chunk of memory for each port */
> INIT_WORK(&tty->hangup_work, release_one_tty);
>
> /*
> * pty_thrash.c
> *
> * Based on original test jig by Ilya Zykov <ilya@ilyx.ru>
> */

Yes, ok with me.
Signed-off-by: Ilya Zykov <ilya@ilyx.ru>

>
> #include <stdio.h>
> #include <fcntl.h>
> #include <sys/ioctl.h>
> #include <termios.h>
> #include <stdlib.h>
> #include <errno.h>
> #include <string.h>
> #include <stdarg.h>
> #include <signal.h>
>
> #define parent child_id
>
> static int fd;
>
> static void error_exit(char *f, ...)
> {
> va_list va;
>
> va_start(va, f);
> vprintf(f, va);
> printf(": %s\n", strerror(errno));
> va_end(va);
>
> if (fd >= 0)
> close(fd);
>
> exit(EXIT_FAILURE);
> }
>
> int main(int argc, char *argv[]) {
> int parent;
> char pts_name[24];
> int ptn, unlock;
>
> while (1) {
>
> fd = open("/dev/ptmx", O_RDWR);
> if (fd < 0)
> error_exit("opening pty master");
> unlock = 0;
> if (ioctl(fd, TIOCSPTLCK, &unlock) < 0)
> error_exit("unlocking pty pair");
> if (ioctl(fd, TIOCGPTN, &ptn) < 0)
> error_exit("getting pty #");
> snprintf(pts_name, sizeof(pts_name), "/dev/pts/%d", ptn);
>
> child_id = fork();
> if (child_id == -1)
> error_exit("forking child");
>
> if (parent) {
> int err, id, status;
> char buf[128];
> int n;
>
> n = read(fd, buf, sizeof(buf));
> if (n < 0)
> error_exit("master reading");
> printf("%.*s\n", n-1, buf);
>
> close(fd);
>
> err = kill(child_id, SIGKILL);
> if (err < 0)
> error_exit("killing child");
> id = waitpid(child_id, &status, 0);
> if (id < 0 || id != child_id)
> error_exit("waiting for child");
>
> } else { /* Child */
>
> close(fd);
> printf("Test cycle on slave pty %s\n", pts_name);
> fd = open(pts_name, O_RDWR);
> if (fd < 0)
> error_exit("opening pty slave");
>
> while (1) {
> char pattern[] = "test\n";
> if (write(fd, pattern, strlen(pattern)) < 0)
> error_exit("slave writing");
> }
>
> }
> }
>
> /* never gets here */
> return 0;
> }
>

Always Welcome.
Ilya.



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