[PATCH v2 0/4] ui/console: chardev backend improvements

[PATCH v2 0/4] ui/console: chardev backend improvements

[Volker Rümelin]

A few things I learnt while writing a fix for a chardev bug
in the GTK backend.

v2:
Patch "ui/console: replace QEMUFIFO with Fifo8". Renamed the
variable free to num_free to help reading the code. (Marc-André)

New patch "ui/console: prevent use after free error".
ui/gtk.c needs a similar patch. I'll take care of it.

Volker Rümelin (4):
   ui/console: replace QEMUFIFO with Fifo8
   ui/console: replace kbd_timer with chr_accept_input callback
   ui/console: remove chardev frontend connected test
   ui/console: prevent use after free error

  ui/console.c | 110 ++++++++++++++-------------------------------------
  1 file changed, 30 insertions(+), 80 deletions(-)

-- 
2.31.1

[PATCH v2 1/4] ui/console: replace QEMUFIFO with Fifo8

[Volker Rümelin]

One of the two FIFO implementations QEMUFIFO and Fifo8 is
redundant. Replace QEMUFIFO with Fifo8.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
---
 ui/console.c | 86 ++++++++++++----------------------------------------
 1 file changed, 20 insertions(+), 66 deletions(-)

diff --git a/ui/console.c b/ui/console.c
index eabbbc951c..d2433c0636 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -27,6 +27,7 @@
 #include "hw/qdev-core.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-ui.h"
+#include "qemu/fifo8.h"
 #include "qemu/module.h"
 #include "qemu/option.h"
 #include "qemu/timer.h"
@@ -62,57 +63,6 @@ enum TTYState {
     TTY_STATE_CSI,
 };
 
-typedef struct QEMUFIFO {
-    uint8_t *buf;
-    int buf_size;
-    int count, wptr, rptr;
-} QEMUFIFO;
-
-static int qemu_fifo_write(QEMUFIFO *f, const uint8_t *buf, int len1)
-{
-    int l, len;
-
-    l = f->buf_size - f->count;
-    if (len1 > l)
-        len1 = l;
-    len = len1;
-    while (len > 0) {
-        l = f->buf_size - f->wptr;
-        if (l > len)
-            l = len;
-        memcpy(f->buf + f->wptr, buf, l);
-        f->wptr += l;
-        if (f->wptr >= f->buf_size)
-            f->wptr = 0;
-        buf += l;
-        len -= l;
-    }
-    f->count += len1;
-    return len1;
-}
-
-static int qemu_fifo_read(QEMUFIFO *f, uint8_t *buf, int len1)
-{
-    int l, len;
-
-    if (len1 > f->count)
-        len1 = f->count;
-    len = len1;
-    while (len > 0) {
-        l = f->buf_size - f->rptr;
-        if (l > len)
-            l = len;
-        memcpy(buf, f->buf + f->rptr, l);
-        f->rptr += l;
-        if (f->rptr >= f->buf_size)
-            f->rptr = 0;
-        buf += l;
-        len -= l;
-    }
-    f->count -= len1;
-    return len1;
-}
-
 typedef enum {
     GRAPHIC_CONSOLE,
     TEXT_CONSOLE,
@@ -165,8 +115,7 @@ struct QemuConsole {
 
     Chardev *chr;
     /* fifo for key pressed */
-    QEMUFIFO out_fifo;
-    uint8_t out_fifo_buf[16];
+    Fifo8 out_fifo;
     QEMUTimer *kbd_timer;
     CoQueue dump_queue;
 
@@ -1160,21 +1109,25 @@ static int vc_chr_write(Chardev *chr, const uint8_t *buf, int len)
 static void kbd_send_chars(void *opaque)
 {
     QemuConsole *s = opaque;
-    int len;
-    uint8_t buf[16];
+    uint32_t len, avail;
 
     len = qemu_chr_be_can_write(s->chr);
-    if (len > s->out_fifo.count)
-        len = s->out_fifo.count;
-    if (len > 0) {
-        if (len > sizeof(buf))
-            len = sizeof(buf);
-        qemu_fifo_read(&s->out_fifo, buf, len);
-        qemu_chr_be_write(s->chr, buf, len);
+    avail = fifo8_num_used(&s->out_fifo);
+    if (len > avail) {
+        len = avail;
+    }
+    while (len > 0) {
+        const uint8_t *buf;
+        uint32_t size;
+
+        buf = fifo8_pop_buf(&s->out_fifo, len, &size);
+        qemu_chr_be_write(s->chr, (uint8_t *)buf, size);
+        len -= size;
+        avail -= size;
     }
     /* characters are pending: we send them a bit later (XXX:
        horrible, should change char device API) */
-    if (s->out_fifo.count > 0) {
+    if (avail > 0) {
         timer_mod(s->kbd_timer, qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + 1);
     }
 }
@@ -1185,6 +1138,7 @@ void kbd_put_keysym_console(QemuConsole *s, int keysym)
     uint8_t buf[16], *q;
     CharBackend *be;
     int c;
+    uint32_t num_free;
 
     if (!s || (s->console_type == GRAPHIC_CONSOLE))
         return;
@@ -1228,7 +1182,8 @@ void kbd_put_keysym_console(QemuConsole *s, int keysym)
         }
         be = s->chr->be;
         if (be && be->chr_read) {
-            qemu_fifo_write(&s->out_fifo, buf, q - buf);
+            num_free = fifo8_num_free(&s->out_fifo);
+            fifo8_push_all(&s->out_fifo, buf, MIN(num_free, q - buf));
             kbd_send_chars(s);
         }
         break;
@@ -2233,8 +2188,7 @@ static void text_console_do_init(Chardev *chr, DisplayState *ds)
     int g_width = 80 * FONT_WIDTH;
     int g_height = 24 * FONT_HEIGHT;
 
-    s->out_fifo.buf = s->out_fifo_buf;
-    s->out_fifo.buf_size = sizeof(s->out_fifo_buf);
+    fifo8_create(&s->out_fifo, 16);
     s->kbd_timer = timer_new_ms(QEMU_CLOCK_REALTIME, kbd_send_chars, s);
     s->ds = ds;
 
-- 
2.31.1

Re: [PATCH v2 1/4] ui/console: replace QEMUFIFO with Fifo8

[Marc-André Lureau]

[-- Attachment #1: Type: text/plain, Size: 4793 bytes --]

On Thu, Sep 16, 2021 at 11:22 PM Volker Rümelin <vr_qemu@t-online.de> wrote:

> One of the two FIFO implementations QEMUFIFO and Fifo8 is
> redundant. Replace QEMUFIFO with Fifo8.
>
> Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

---
>  ui/console.c | 86 ++++++++++++----------------------------------------
>  1 file changed, 20 insertions(+), 66 deletions(-)
>
> diff --git a/ui/console.c b/ui/console.c
> index eabbbc951c..d2433c0636 100644
> --- a/ui/console.c
> +++ b/ui/console.c
> @@ -27,6 +27,7 @@
>  #include "hw/qdev-core.h"
>  #include "qapi/error.h"
>  #include "qapi/qapi-commands-ui.h"
> +#include "qemu/fifo8.h"
>  #include "qemu/module.h"
>  #include "qemu/option.h"
>  #include "qemu/timer.h"
> @@ -62,57 +63,6 @@ enum TTYState {
>      TTY_STATE_CSI,
>  };
>
> -typedef struct QEMUFIFO {
> -    uint8_t *buf;
> -    int buf_size;
> -    int count, wptr, rptr;
> -} QEMUFIFO;
> -
> -static int qemu_fifo_write(QEMUFIFO *f, const uint8_t *buf, int len1)
> -{
> -    int l, len;
> -
> -    l = f->buf_size - f->count;
> -    if (len1 > l)
> -        len1 = l;
> -    len = len1;
> -    while (len > 0) {
> -        l = f->buf_size - f->wptr;
> -        if (l > len)
> -            l = len;
> -        memcpy(f->buf + f->wptr, buf, l);
> -        f->wptr += l;
> -        if (f->wptr >= f->buf_size)
> -            f->wptr = 0;
> -        buf += l;
> -        len -= l;
> -    }
> -    f->count += len1;
> -    return len1;
> -}
> -
> -static int qemu_fifo_read(QEMUFIFO *f, uint8_t *buf, int len1)
> -{
> -    int l, len;
> -
> -    if (len1 > f->count)
> -        len1 = f->count;
> -    len = len1;
> -    while (len > 0) {
> -        l = f->buf_size - f->rptr;
> -        if (l > len)
> -            l = len;
> -        memcpy(buf, f->buf + f->rptr, l);
> -        f->rptr += l;
> -        if (f->rptr >= f->buf_size)
> -            f->rptr = 0;
> -        buf += l;
> -        len -= l;
> -    }
> -    f->count -= len1;
> -    return len1;
> -}
> -
>  typedef enum {
>      GRAPHIC_CONSOLE,
>      TEXT_CONSOLE,
> @@ -165,8 +115,7 @@ struct QemuConsole {
>
>      Chardev *chr;
>      /* fifo for key pressed */
> -    QEMUFIFO out_fifo;
> -    uint8_t out_fifo_buf[16];
> +    Fifo8 out_fifo;
>      QEMUTimer *kbd_timer;
>      CoQueue dump_queue;
>
> @@ -1160,21 +1109,25 @@ static int vc_chr_write(Chardev *chr, const
> uint8_t *buf, int len)
>  static void kbd_send_chars(void *opaque)
>  {
>      QemuConsole *s = opaque;
> -    int len;
> -    uint8_t buf[16];
> +    uint32_t len, avail;
>
>      len = qemu_chr_be_can_write(s->chr);
> -    if (len > s->out_fifo.count)
> -        len = s->out_fifo.count;
> -    if (len > 0) {
> -        if (len > sizeof(buf))
> -            len = sizeof(buf);
> -        qemu_fifo_read(&s->out_fifo, buf, len);
> -        qemu_chr_be_write(s->chr, buf, len);
> +    avail = fifo8_num_used(&s->out_fifo);
> +    if (len > avail) {
> +        len = avail;
> +    }
> +    while (len > 0) {
> +        const uint8_t *buf;
> +        uint32_t size;
> +
> +        buf = fifo8_pop_buf(&s->out_fifo, len, &size);
> +        qemu_chr_be_write(s->chr, (uint8_t *)buf, size);
> +        len -= size;
> +        avail -= size;
>      }
>      /* characters are pending: we send them a bit later (XXX:
>         horrible, should change char device API) */
> -    if (s->out_fifo.count > 0) {
> +    if (avail > 0) {
>          timer_mod(s->kbd_timer, qemu_clock_get_ms(QEMU_CLOCK_REALTIME) +
> 1);
>      }
>  }
> @@ -1185,6 +1138,7 @@ void kbd_put_keysym_console(QemuConsole *s, int
> keysym)
>      uint8_t buf[16], *q;
>      CharBackend *be;
>      int c;
> +    uint32_t num_free;
>
>      if (!s || (s->console_type == GRAPHIC_CONSOLE))
>          return;
> @@ -1228,7 +1182,8 @@ void kbd_put_keysym_console(QemuConsole *s, int
> keysym)
>          }
>          be = s->chr->be;
>          if (be && be->chr_read) {
> -            qemu_fifo_write(&s->out_fifo, buf, q - buf);
> +            num_free = fifo8_num_free(&s->out_fifo);
> +            fifo8_push_all(&s->out_fifo, buf, MIN(num_free, q - buf));
>              kbd_send_chars(s);
>          }
>          break;
> @@ -2233,8 +2188,7 @@ static void text_console_do_init(Chardev *chr,
> DisplayState *ds)
>      int g_width = 80 * FONT_WIDTH;
>      int g_height = 24 * FONT_HEIGHT;
>
> -    s->out_fifo.buf = s->out_fifo_buf;
> -    s->out_fifo.buf_size = sizeof(s->out_fifo_buf);
> +    fifo8_create(&s->out_fifo, 16);
>      s->kbd_timer = timer_new_ms(QEMU_CLOCK_REALTIME, kbd_send_chars, s);
>      s->ds = ds;
>
> --
> 2.31.1
>
>

[-- Attachment #2: Type: text/html, Size: 6327 bytes --]

[PATCH v2 2/4] ui/console: replace kbd_timer with chr_accept_input callback

[Volker Rümelin]

There's a ChardevClass chr_accept_input() callback function that
can replace the write retry timer.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
---
 ui/console.c | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/ui/console.c b/ui/console.c
index d2433c0636..dda1e6861d 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -116,7 +116,6 @@ struct QemuConsole {
     Chardev *chr;
     /* fifo for key pressed */
     Fifo8 out_fifo;
-    QEMUTimer *kbd_timer;
     CoQueue dump_queue;
 
     QTAILQ_ENTRY(QemuConsole) next;
@@ -1106,30 +1105,21 @@ static int vc_chr_write(Chardev *chr, const uint8_t *buf, int len)
     return len;
 }
 
-static void kbd_send_chars(void *opaque)
+static void kbd_send_chars(QemuConsole *s)
 {
-    QemuConsole *s = opaque;
     uint32_t len, avail;
 
     len = qemu_chr_be_can_write(s->chr);
     avail = fifo8_num_used(&s->out_fifo);
-    if (len > avail) {
-        len = avail;
-    }
-    while (len > 0) {
+    while (len > 0 && avail > 0) {
         const uint8_t *buf;
         uint32_t size;
 
-        buf = fifo8_pop_buf(&s->out_fifo, len, &size);
+        buf = fifo8_pop_buf(&s->out_fifo, MIN(len, avail), &size);
         qemu_chr_be_write(s->chr, (uint8_t *)buf, size);
-        len -= size;
+        len = qemu_chr_be_can_write(s->chr);
         avail -= size;
     }
-    /* characters are pending: we send them a bit later (XXX:
-       horrible, should change char device API) */
-    if (avail > 0) {
-        timer_mod(s->kbd_timer, qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + 1);
-    }
 }
 
 /* called when an ascii key is pressed */
@@ -2141,6 +2131,14 @@ int qemu_console_get_height(QemuConsole *con, int fallback)
     return con ? surface_height(con->surface) : fallback;
 }
 
+static void vc_chr_accept_input(Chardev *chr)
+{
+    VCChardev *drv = VC_CHARDEV(chr);
+    QemuConsole *s = drv->console;
+
+    kbd_send_chars(s);
+}
+
 static void vc_chr_set_echo(Chardev *chr, bool echo)
 {
     VCChardev *drv = VC_CHARDEV(chr);
@@ -2189,7 +2187,6 @@ static void text_console_do_init(Chardev *chr, DisplayState *ds)
     int g_height = 24 * FONT_HEIGHT;
 
     fifo8_create(&s->out_fifo, 16);
-    s->kbd_timer = timer_new_ms(QEMU_CLOCK_REALTIME, kbd_send_chars, s);
     s->ds = ds;
 
     s->y_displayed = 0;
@@ -2439,6 +2436,7 @@ static void char_vc_class_init(ObjectClass *oc, void *data)
     cc->parse = qemu_chr_parse_vc;
     cc->open = vc_chr_open;
     cc->chr_write = vc_chr_write;
+    cc->chr_accept_input = vc_chr_accept_input;
     cc->chr_set_echo = vc_chr_set_echo;
 }
 
-- 
2.31.1

[PATCH v2 3/4] ui/console: remove chardev frontend connected test

[Volker Rümelin]

The test if the chardev frontend is connected in
kbd_put_keysym_console() is redundant, because the call
to qemu_chr_be_can_write() in kbd_send_chars() tests
the connected condition again.

Remove the redundant test whether the chardev frontend
is connected.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
---
 ui/console.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/ui/console.c b/ui/console.c
index dda1e6861d..29a3e3f0f5 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -28,10 +28,11 @@
 #include "qapi/error.h"
 #include "qapi/qapi-commands-ui.h"
 #include "qemu/fifo8.h"
+#include "qemu/main-loop.h"
 #include "qemu/module.h"
 #include "qemu/option.h"
 #include "qemu/timer.h"
-#include "chardev/char-fe.h"
+#include "chardev/char.h"
 #include "trace.h"
 #include "exec/memory.h"
 #include "io/channel-file.h"
@@ -1126,7 +1127,6 @@ static void kbd_send_chars(QemuConsole *s)
 void kbd_put_keysym_console(QemuConsole *s, int keysym)
 {
     uint8_t buf[16], *q;
-    CharBackend *be;
     int c;
     uint32_t num_free;
 
@@ -1170,12 +1170,9 @@ void kbd_put_keysym_console(QemuConsole *s, int keysym)
         if (s->echo) {
             vc_chr_write(s->chr, buf, q - buf);
         }
-        be = s->chr->be;
-        if (be && be->chr_read) {
-            num_free = fifo8_num_free(&s->out_fifo);
-            fifo8_push_all(&s->out_fifo, buf, MIN(num_free, q - buf));
-            kbd_send_chars(s);
-        }
+        num_free = fifo8_num_free(&s->out_fifo);
+        fifo8_push_all(&s->out_fifo, buf, MIN(num_free, q - buf));
+        kbd_send_chars(s);
         break;
     }
 }
-- 
2.31.1

[PATCH v2 4/4] ui/console: prevent use after free error

[Volker Rümelin]

Make chr in the QemuConsole object a strong reference to the
referenced chardev device. This prevents a use after free error
if the chardev device goes away unexpectedly.

To reproduce the error start qemu-system built with address
sanitizer with the the following command line options.

-display sdl -chardev vc,id=test0,cols=132,rows=50.

Open the monitor console with CTRL-ALT-3 and remove the
unconnected chardev device test0.

(qemu) chardev-remove test0

Open the text console test0 with CTRL-ALT-2 and type a character.
QEMU immediately exits with this error message.

==28148==ERROR: AddressSanitizer: heap-use-after-free
  on address 0x60e000043778 at pc 0x558712ba7125
  bp 0x7fff270980b0 sp 0x7fff270980a8
READ of size 8 at 0x60e000043778 thread T0
    #0 0x558712ba7124 in qemu_chr_be_can_write
      ../qemu-master/chardev/char.c:188
    #1 0x558711624770 in kbd_send_chars
      ../qemu-master/ui/console.c:1113
    #2 0x558711634e91 in kbd_put_keysym_console
      ../qemu-master/ui/console.c:1175
    #3 0x55871163532a in kbd_put_string_console
      ../qemu-master/ui/console.c:1221
    #4 0x5587120a21e4 in handle_textinput
      ../qemu-master/ui/sdl2.c:464
    #5 0x5587120a21e4 in sdl2_poll_events
      ../qemu-master/ui/sdl2.c:650
    #6 0x5587116269c3 in dpy_refresh
      ../qemu-master/ui/console.c:1673
    #7 0x5587116269c3 in gui_update
      ../qemu-master/ui/console.c:158
    #8 0x558712d3a919 in timerlist_run_timers
      ../qemu-master/util/qemu-timer.c:573
    #9 0x558712d3b183 in qemu_clock_run_timers
      ../qemu-master/util/qemu-timer.c:587
    #10 0x558712d3b183 in qemu_clock_run_all_timers
      ../qemu-master/util/qemu-timer.c:669
    #11 0x558712d286d9 in main_loop_wait
      ../qemu-master/util/main-loop.c:542
    #12 0x5587123d313b in qemu_main_loop
      ../qemu-master/softmmu/runstate.c:726
    #13 0x5587115f989d in main
      ../qemu-master/softmmu/main.c:50
    #14 0x7f832ee0934c in __libc_start_main
      (/lib64/libc.so.6+0x2534c)
    #15 0x55871160b6e9 in _start
      (/home/ruemelin/rpmbuild/BUILD/qemu-6.1.50-build/
      qemu-system-x86_64+0x1f4f6e9)

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
---
 ui/console.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/ui/console.c b/ui/console.c
index 29a3e3f0f5..1ef5a96295 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -2264,6 +2264,7 @@ static void vc_chr_open(Chardev *chr,
     }
 
     s->chr = chr;
+    object_ref(chr);
     drv->console = s;
 
     if (display_state) {
-- 
2.31.1

Re: [PATCH v2 4/4] ui/console: prevent use after free error

[Marc-André Lureau]

[-- Attachment #1: Type: text/plain, Size: 3058 bytes --]

Hi

On Thu, Sep 16, 2021 at 11:29 PM Volker Rümelin <vr_qemu@t-online.de> wrote:

> Make chr in the QemuConsole object a strong reference to the
> referenced chardev device. This prevents a use after free error
> if the chardev device goes away unexpectedly.
>
> To reproduce the error start qemu-system built with address
> sanitizer with the the following command line options.
>
> -display sdl -chardev vc,id=test0,cols=132,rows=50.
>
> Open the monitor console with CTRL-ALT-3 and remove the
> unconnected chardev device test0.
>
> (qemu) chardev-remove test0
>
> Open the text console test0 with CTRL-ALT-2 and type a character.
> QEMU immediately exits with this error message.
>

Hmm, why is it not busy like the other chardevs?


> ==28148==ERROR: AddressSanitizer: heap-use-after-free
>   on address 0x60e000043778 at pc 0x558712ba7125
>   bp 0x7fff270980b0 sp 0x7fff270980a8
> READ of size 8 at 0x60e000043778 thread T0
>     #0 0x558712ba7124 in qemu_chr_be_can_write
>       ../qemu-master/chardev/char.c:188
>     #1 0x558711624770 in kbd_send_chars
>       ../qemu-master/ui/console.c:1113
>     #2 0x558711634e91 in kbd_put_keysym_console
>       ../qemu-master/ui/console.c:1175
>     #3 0x55871163532a in kbd_put_string_console
>       ../qemu-master/ui/console.c:1221
>     #4 0x5587120a21e4 in handle_textinput
>       ../qemu-master/ui/sdl2.c:464
>     #5 0x5587120a21e4 in sdl2_poll_events
>       ../qemu-master/ui/sdl2.c:650
>     #6 0x5587116269c3 in dpy_refresh
>       ../qemu-master/ui/console.c:1673
>     #7 0x5587116269c3 in gui_update
>       ../qemu-master/ui/console.c:158
>     #8 0x558712d3a919 in timerlist_run_timers
>       ../qemu-master/util/qemu-timer.c:573
>     #9 0x558712d3b183 in qemu_clock_run_timers
>       ../qemu-master/util/qemu-timer.c:587
>     #10 0x558712d3b183 in qemu_clock_run_all_timers
>       ../qemu-master/util/qemu-timer.c:669
>     #11 0x558712d286d9 in main_loop_wait
>       ../qemu-master/util/main-loop.c:542
>     #12 0x5587123d313b in qemu_main_loop
>       ../qemu-master/softmmu/runstate.c:726
>     #13 0x5587115f989d in main
>       ../qemu-master/softmmu/main.c:50
>     #14 0x7f832ee0934c in __libc_start_main
>       (/lib64/libc.so.6+0x2534c)
>     #15 0x55871160b6e9 in _start
>       (/home/ruemelin/rpmbuild/BUILD/qemu-6.1.50-build/
>       qemu-system-x86_64+0x1f4f6e9)
>
> Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
> ---
>  ui/console.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/ui/console.c b/ui/console.c
> index 29a3e3f0f5..1ef5a96295 100644
> --- a/ui/console.c
> +++ b/ui/console.c
> @@ -2264,6 +2264,7 @@ static void vc_chr_open(Chardev *chr,
>      }
>
>      s->chr = chr;
> +    object_ref(chr);
>      drv->console = s;
>
>      if (display_state) {
>

Isn't this effectively preventing removing the chardev? Hence, it should
either be made busy, or keeping a weak pointer invalidated on
instance_finalize imho.

thanks


-- 
Marc-André Lureau

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