[PATCH] char: don't fail when client is not connected

[PATCH] char: don't fail when client is not connected

[Pavel Dovgalyuk]

This patch checks that ioc is not null before
using it in tcp socket tcp_chr_add_watch function.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
---
 chardev/char-socket.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 213a4c8dd0..cef1d9438f 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -385,6 +385,9 @@ static ssize_t tcp_chr_recv(Chardev *chr, char *buf, size_t len)
 static GSource *tcp_chr_add_watch(Chardev *chr, GIOCondition cond)
 {
     SocketChardev *s = SOCKET_CHARDEV(chr);
+    if (!s->ioc) {
+        return NULL;
+    }
     return qio_channel_create_watch(s->ioc, cond);
 }
 

Re: [PATCH] char: don't fail when client is not connected

[Marc-André Lureau]

[-- Attachment #1: Type: text/plain, Size: 889 bytes --]

Hi

On Tue, Feb 2, 2021 at 11:18 AM Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>
wrote:

> This patch checks that ioc is not null before
> using it in tcp socket tcp_chr_add_watch function.
>
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
>

Do you have a backtrace or a reproducer when this happens?
thanks

---
>  chardev/char-socket.c |    3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/chardev/char-socket.c b/chardev/char-socket.c
> index 213a4c8dd0..cef1d9438f 100644
> --- a/chardev/char-socket.c
> +++ b/chardev/char-socket.c
> @@ -385,6 +385,9 @@ static ssize_t tcp_chr_recv(Chardev *chr, char *buf,
> size_t len)
>  static GSource *tcp_chr_add_watch(Chardev *chr, GIOCondition cond)
>  {
>      SocketChardev *s = SOCKET_CHARDEV(chr);
> +    if (!s->ioc) {
> +        return NULL;
> +    }
>      return qio_channel_create_watch(s->ioc, cond);
>  }
>
>
>

[-- Attachment #2: Type: text/html, Size: 1546 bytes --]

Re: [PATCH] char: don't fail when client is not connected

[Pavel Dovgalyuk]

On 02.02.2021 10:27, Marc-André Lureau wrote:
> Hi
> 
> On Tue, Feb 2, 2021 at 11:18 AM Pavel Dovgalyuk 
> <pavel.dovgalyuk@ispras.ru <mailto:pavel.dovgalyuk@ispras.ru>> wrote:
> 
>     This patch checks that ioc is not null before
>     using it in tcp socket tcp_chr_add_watch function.
> 
>     Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru
>     <mailto:Pavel.Dovgalyuk@ispras.ru>>
> 
> 
> Do you have a backtrace or a reproducer when this happens?
> thanks

Here is the backtrace:

Thread 4 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff2506700 (LWP 64988)]
object_get_class (obj=obj@entry=0x0) at ../qom/object.c:999
999	    return obj->class;
(gdb) bt
#0  object_get_class (obj=obj@entry=0x0) at ../qom/object.c:999
#1  0x0000555555b70e26 in QIO_CHANNEL_GET_CLASS (obj=0x0) at 
/home/pasha/ispras/qemu-test/include/io/channel.h:29
#2  qio_channel_create_watch (ioc=0x0, condition=(G_IO_OUT | G_IO_HUP)) 
at ../io/channel.c:281
#3  0x0000555555c1bf9b in qemu_chr_fe_add_watch
     (be=be@entry=0x555556981648, cond=cond@entry=(G_IO_OUT | G_IO_HUP), 
func=func@entry=0x55555597f170 <serial_watch_cb>, 
user_data=user_data@entry=0x5555569815a0)
     at /home/pasha/ispras/qemu-test/include/chardev/char.h:229
#4  0x000055555597f042 in serial_xmit (s=s@entry=0x5555569815a0) at 
../hw/char/serial.c:265
#5  0x000055555597f437 in serial_ioport_write (opaque=0x5555569815a0, 
addr=<optimized out>, val=91, size=<optimized out>) at 
../hw/char/serial.c:359
#6  0x0000555555ab95e0 in memory_region_write_accessor 
(mr=mr@entry=0x555556981700, addr=0, value=value@entry=0x7ffff2504fc8, 
size=size@entry=1, shift=<optimized out>, mask=mask@entry=255, attrs=...)
     at ../softmmu/memory.c:491
#7  0x0000555555ab807e in access_with_adjusted_size
     (addr=addr@entry=0, value=value@entry=0x7ffff2504fc8, 
size=size@entry=1, access_size_min=<optimized out>, 
access_size_max=<optimized out>, access_fn=access_fn@entry=
     0x555555ab9550 <memory_region_write_accessor>, mr=0x555556981700, 
attrs=...) at ../softmmu/memory.c:552
#8  0x0000555555abb947 in memory_region_dispatch_write 
(mr=mr@entry=0x555556981700, addr=0, data=<optimized out>, 
data@entry=91, op=op@entry=MO_8, attrs=attrs@entry=...) at 
../softmmu/memory.c:1501
#9  0x0000555555a721d8 in address_space_stb (as=<optimized out>, 
addr=<optimized out>, val=91, attrs=..., result=0x0) at 
/home/pasha/ispras/qemu-test/memory_ldst.c.inc:382
#10 0x00007fffa8b63022 in code_gen_buffer ()
#11 0x0000555555b10ab0 in cpu_tb_exec (tb_exit=<synthetic pointer>, 
itb=<optimized out>, cpu=0x7fffa8635b00 <code_gen_buffer+73620179>) at 
../accel/tcg/cpu-exec.c:188
#12 cpu_loop_exec_tb (tb_exit=<synthetic pointer>, last_tb=<synthetic 
pointer>, tb=<optimized out>, cpu=0x7fffa8635b00 
<code_gen_buffer+73620179>) at ../accel/tcg/cpu-exec.c:700
#13 cpu_exec (cpu=cpu@entry=0x5555566b4350) at ../accel/tcg/cpu-exec.c:811
#14 0x0000555555b0ce97 in tcg_cpus_exec (cpu=cpu@entry=0x5555566b4350) 
at ../accel/tcg/tcg-cpus.c:57
#15 0x0000555555abfa73 in rr_cpu_thread_fn 
(arg=arg@entry=0x5555566b4350) at ../accel/tcg/tcg-cpus-rr.c:217
#16 0x0000555555c80573 in qemu_thread_start (args=<optimized out>) at 
../util/qemu-thread-posix.c:521
#17 0x00007ffff6302609 in start_thread (arg=<optimized out>) at 
pthread_create.c:477
#18 0x00007ffff6229293 in clone () at 
../sysdeps/unix/sysv/linux/x86_64/clone.S:95


> 
>     ---
>       chardev/char-socket.c |    3 +++
>       1 file changed, 3 insertions(+)
> 
>     diff --git a/chardev/char-socket.c b/chardev/char-socket.c
>     index 213a4c8dd0..cef1d9438f 100644
>     --- a/chardev/char-socket.c
>     +++ b/chardev/char-socket.c
>     @@ -385,6 +385,9 @@ static ssize_t tcp_chr_recv(Chardev *chr, char
>     *buf, size_t len)
>       static GSource *tcp_chr_add_watch(Chardev *chr, GIOCondition cond)
>       {
>           SocketChardev *s = SOCKET_CHARDEV(chr);
>     +    if (!s->ioc) {
>     +        return NULL;
>     +    }
>           return qio_channel_create_watch(s->ioc, cond);
>       }
> 
> 

Re: [PATCH] char: don't fail when client is not connected

[Marc-André Lureau]

[-- Attachment #1: Type: text/plain, Size: 3150 bytes --]

Hi

On Tue, Feb 2, 2021 at 11:33 AM Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>
wrote:

> On 02.02.2021 10:27, Marc-André Lureau wrote:
> > Hi
> >
> > On Tue, Feb 2, 2021 at 11:18 AM Pavel Dovgalyuk
> > <pavel.dovgalyuk@ispras.ru <mailto:pavel.dovgalyuk@ispras.ru>> wrote:
> >
> >     This patch checks that ioc is not null before
> >     using it in tcp socket tcp_chr_add_watch function.
> >
> >     Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru
> >     <mailto:Pavel.Dovgalyuk@ispras.ru>>
> >
> >
> > Do you have a backtrace or a reproducer when this happens?
> > thanks
>
> Here is the backtrace:
>
> Thread 4 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7ffff2506700 (LWP 64988)]
> object_get_class (obj=obj@entry=0x0) at ../qom/object.c:999
> 999         return obj->class;
> (gdb) bt
> #0  object_get_class (obj=obj@entry=0x0) at ../qom/object.c:999
> #1  0x0000555555b70e26 in QIO_CHANNEL_GET_CLASS (obj=0x0) at
> /home/pasha/ispras/qemu-test/include/io/channel.h:29
> #2  qio_channel_create_watch (ioc=0x0, condition=(G_IO_OUT | G_IO_HUP))
> at ../io/channel.c:281
> #3  0x0000555555c1bf9b in qemu_chr_fe_add_watch
>      (be=be@entry=0x555556981648, cond=cond@entry=(G_IO_OUT | G_IO_HUP),
> func=func@entry=0x55555597f170 <serial_watch_cb>,
> user_data=user_data@entry=0x5555569815a0)
>      at /home/pasha/ispras/qemu-test/include/chardev/char.h:229
> #4  0x000055555597f042 in serial_xmit (s=s@entry=0x5555569815a0) at
> ../hw/char/serial.c:265
> #5  0x000055555597f437 in serial_ioport_write (opaque=0x5555569815a0,
> addr=<optimized out>, val=91, size=<optimized out>) at
> ../hw/char/serial.c:359
>

Thanks, I don't understand how this could happen.

serial_xmit:
           int rc = qemu_chr_fe_write(&s->chr, &s->tsr, 1);

            if ((rc == 0 ||
                 (rc == -1 && errno == EAGAIN)) &&
                s->tsr_retry < MAX_XMIT_RETRY) {
                assert(s->watch_tag == 0);
                s->watch_tag =
                    qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
                                          serial_watch_cb, s);

The watch is added only if fe_write() returned 0 || -1 with EAGAIN.

But tcp_chr_write() should return -1 with EIO if the state is disconnected
(and ioc is NULL), or other errors on disconnect.

Can you provide a reproducer?

thanks


> >
> >     ---
> >       chardev/char-socket.c |    3 +++
> >       1 file changed, 3 insertions(+)
> >
> >     diff --git a/chardev/char-socket.c b/chardev/char-socket.c
> >     index 213a4c8dd0..cef1d9438f 100644
> >     --- a/chardev/char-socket.c
> >     +++ b/chardev/char-socket.c
> >     @@ -385,6 +385,9 @@ static ssize_t tcp_chr_recv(Chardev *chr, char
> >     *buf, size_t len)
> >       static GSource *tcp_chr_add_watch(Chardev *chr, GIOCondition cond)
> >       {
> >           SocketChardev *s = SOCKET_CHARDEV(chr);
> >     +    if (!s->ioc) {
> >     +        return NULL;
> >     +    }
> >           return qio_channel_create_watch(s->ioc, cond);
> >       }
> >
> >
>
>

[-- Attachment #2: Type: text/html, Size: 4863 bytes --]

Re: [PATCH] char: don't fail when client is not connected

[Pavel Dovgalyuk]

On 03.02.2021 11:13, Marc-André Lureau wrote:
> Hi
> 
> On Tue, Feb 2, 2021 at 11:33 AM Pavel Dovgalyuk 
> <pavel.dovgalyuk@ispras.ru <mailto:pavel.dovgalyuk@ispras.ru>> wrote:
> 
>     On 02.02.2021 10:27, Marc-André Lureau wrote:
>      > Hi
>      >
>      > On Tue, Feb 2, 2021 at 11:18 AM Pavel Dovgalyuk
>      > <pavel.dovgalyuk@ispras.ru <mailto:pavel.dovgalyuk@ispras.ru>
>     <mailto:pavel.dovgalyuk@ispras.ru
>     <mailto:pavel.dovgalyuk@ispras.ru>>> wrote:
>      >
>      >     This patch checks that ioc is not null before
>      >     using it in tcp socket tcp_chr_add_watch function.
>      >
>      >     Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru
>     <mailto:Pavel.Dovgalyuk@ispras.ru>
>      >     <mailto:Pavel.Dovgalyuk@ispras.ru
>     <mailto:Pavel.Dovgalyuk@ispras.ru>>>
>      >
>      >
>      > Do you have a backtrace or a reproducer when this happens?
>      > thanks
> 
>     Here is the backtrace:
> 
>     Thread 4 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
>     [Switching to Thread 0x7ffff2506700 (LWP 64988)]
>     object_get_class (obj=obj@entry=0x0) at ../qom/object.c:999
>     999         return obj->class;
>     (gdb) bt
>     #0  object_get_class (obj=obj@entry=0x0) at ../qom/object.c:999
>     #1  0x0000555555b70e26 in QIO_CHANNEL_GET_CLASS (obj=0x0) at
>     /home/pasha/ispras/qemu-test/include/io/channel.h:29
>     #2  qio_channel_create_watch (ioc=0x0, condition=(G_IO_OUT | G_IO_HUP))
>     at ../io/channel.c:281
>     #3  0x0000555555c1bf9b in qemu_chr_fe_add_watch
>           (be=be@entry=0x555556981648, cond=cond@entry=(G_IO_OUT |
>     G_IO_HUP),
>     func=func@entry=0x55555597f170 <serial_watch_cb>,
>     user_data=user_data@entry=0x5555569815a0)
>           at /home/pasha/ispras/qemu-test/include/chardev/char.h:229
>     #4  0x000055555597f042 in serial_xmit (s=s@entry=0x5555569815a0) at
>     ../hw/char/serial.c:265
>     #5  0x000055555597f437 in serial_ioport_write (opaque=0x5555569815a0,
>     addr=<optimized out>, val=91, size=<optimized out>) at
>     ../hw/char/serial.c:359
> 
> 
> Thanks, I don't understand how this could happen.
> 
> serial_xmit:
>             int rc = qemu_chr_fe_write(&s->chr, &s->tsr, 1);
> 
>              if ((rc == 0 ||
>                   (rc == -1 && errno == EAGAIN)) &&
>                  s->tsr_retry < MAX_XMIT_RETRY) {
>                  assert(s->watch_tag == 0);
>                  s->watch_tag =
>                      qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
>                                            serial_watch_cb, s);
> 
> The watch is added only if fe_write() returned 0 || -1 with EAGAIN.
> 
> But tcp_chr_write() should return -1 with EIO if the state is 
> disconnected (and ioc is NULL), or other errors on disconnect.
> 
> Can you provide a reproducer?


That was a record/replay scenario. I've used Fedora cloudinit images, 
that are used in acceptance tests:

qemu-system-x86_64 \
  -display none -vga none -machine pc -smp 1 -m 1024 \
  -monitor tcp:127.0.0.1:8081,server,nowait \
  -serial tcp:127.0.0.1:8082,server,nowait \
  -object filter-replay,id=replay,netdev=hub0port0 \
  -drive 
file=Fedora-Cloud-Base-31-1.9.x86_64.qcow2,snapshot,id=disk0,if=none \
  -drive driver=blkreplay,id=disk0-rr,if=none,image=disk0 \
  -device virtio-blk-pci,drive=disk0-rr,ioeventfd=false \
  -icount shift=1,rr=record,rrfile=replay.bin \
  -drive file=cloudinit.iso,snapshot,id=disk1,if=none \
  -drive driver=blkreplay,id=disk1-rr,if=none,image=disk1 \
  -device virtio-blk-pci,drive=disk1-rr,ioeventfd=false


The failure occurred on replay stage:

qemu-system-x86_64 \
  -display none -vga none -machine pc -smp 1 -m 1024 \
  -monitor tcp:127.0.0.1:8081,server,nowait \
  -serial tcp:127.0.0.1:8082,server,nowait \
  -object filter-replay,id=replay,netdev=hub0port0 \
  -drive 
file=Fedora-Cloud-Base-31-1.9.x86_64.qcow2,snapshot,id=disk0,if=none \
  -drive driver=blkreplay,id=disk0-rr,if=none,image=disk0 \
  -device virtio-blk-pci,drive=disk0-rr,ioeventfd=false \
  -icount shift=1,rr=replay,rrfile=replay.bin \
  -drive file=cloudinit.iso,snapshot,id=disk1,if=none \
  -drive driver=blkreplay,id=disk1-rr,if=none,image=disk1 \
  -device virtio-blk-pci,drive=disk1-rr,ioeventfd=false

> 
> thanks
> 
> 
>      >
>      >     ---
>      >       chardev/char-socket.c |    3 +++
>      >       1 file changed, 3 insertions(+)
>      >
>      >     diff --git a/chardev/char-socket.c b/chardev/char-socket.c
>      >     index 213a4c8dd0..cef1d9438f 100644
>      >     --- a/chardev/char-socket.c
>      >     +++ b/chardev/char-socket.c
>      >     @@ -385,6 +385,9 @@ static ssize_t tcp_chr_recv(Chardev *chr,
>     char
>      >     *buf, size_t len)
>      >       static GSource *tcp_chr_add_watch(Chardev *chr,
>     GIOCondition cond)
>      >       {
>      >           SocketChardev *s = SOCKET_CHARDEV(chr);
>      >     +    if (!s->ioc) {
>      >     +        return NULL;
>      >     +    }
>      >           return qio_channel_create_watch(s->ioc, cond);
>      >       }
>      >
>      >
> 

Re: [PATCH] char: don't fail when client is not connected

[Marc-André Lureau]

[-- Attachment #1: Type: text/plain, Size: 2205 bytes --]

Hi

On Wed, Feb 3, 2021 at 12:22 PM Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>
wrote:

> On 03.02.2021 11:13, Marc-André Lureau wrote:
>
> > Can you provide a reproducer?
>
>
> That was a record/replay scenario. I've used Fedora cloudinit images,
> that are used in acceptance tests:
>
> qemu-system-x86_64 \
>   -display none -vga none -machine pc -smp 1 -m 1024 \
>   -monitor tcp:127.0.0.1:8081,server,nowait \
>   -serial tcp:127.0.0.1:8082,server,nowait \
>   -object filter-replay,id=replay,netdev=hub0port0 \
>   -drive
> file=Fedora-Cloud-Base-31-1.9.x86_64.qcow2,snapshot,id=disk0,if=none \
>   -drive driver=blkreplay,id=disk0-rr,if=none,image=disk0 \
>   -device virtio-blk-pci,drive=disk0-rr,ioeventfd=false \
>   -icount shift=1,rr=record,rrfile=replay.bin \
>   -drive file=cloudinit.iso,snapshot,id=disk1,if=none \
>   -drive driver=blkreplay,id=disk1-rr,if=none,image=disk1 \
>   -device virtio-blk-pci,drive=disk1-rr,ioeventfd=false
>
>
> The failure occurred on replay stage:
>
> qemu-system-x86_64 \
>   -display none -vga none -machine pc -smp 1 -m 1024 \
>   -monitor tcp:127.0.0.1:8081,server,nowait \
>   -serial tcp:127.0.0.1:8082,server,nowait \
>   -object filter-replay,id=replay,netdev=hub0port0 \
>   -drive
> file=Fedora-Cloud-Base-31-1.9.x86_64.qcow2,snapshot,id=disk0,if=none \
>   -drive driver=blkreplay,id=disk0-rr,if=none,image=disk0 \
>   -device virtio-blk-pci,drive=disk0-rr,ioeventfd=false \
>   -icount shift=1,rr=replay,rrfile=replay.bin \
>   -drive file=cloudinit.iso,snapshot,id=disk1,if=none \
>   -drive driver=blkreplay,id=disk1-rr,if=none,image=disk1 \
>   -device virtio-blk-pci,drive=disk1-rr,ioeventfd=false
>

Ah, that helps. qemu_chr_write() will return
replay_char_write_event_load(), bypassing the current state. If the
connected state during replay doesn't match the state during recording, it
is possible to reach the bad condition. (there are probably many such
corner-cases situations with replay..)

Can you update the commit message to explain the relation with replay? with
that:
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Daniel, could you review it too?
thanks

[-- Attachment #2: Type: text/html, Size: 3047 bytes --]