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Re: [Qemu-devel] segmentation fault in qemu-kvm-0.14.0

From: Stefan Weil
Subject: Re: [Qemu-devel] segmentation fault in qemu-kvm-0.14.0
Date: Tue, 15 Mar 2011 19:52:27 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20101226 Iceowl/1.0b1 Icedove/3.0.11 
Am 15.03.2011 13:53, schrieb Peter Lieven:

On 09.03.2011 08:26, Stefan Weil wrote:

Am 08.03.2011 23:53, schrieb Peter Lieven:

Hi,
during testing of qemu-kvm-0.14.0 i can reproduce the following segfault. i have seen similar crash already in 0.13.0, but had no time to debug. my guess is that this segfault is related to the threaded vnc server which was introduced in qemu 0.13.0. the bug is only triggerable if a vnc client is attached. it might also be connected to a resolution change in the guest. i have a backtrace attached. the debugger is still running if someone 
needs more output

Reading symbols from /usr/local/bin/qemu-system-x86_64...done.
(gdb) r -net tap,vlan=141,script=no,downscript=no,ifname=tap0 -net nic,vlan=141,model=rtl8139,macaddr=52:54:00:ff:00:93 -drive format=host_device,file=/dev/mapper/iqn.2001-05.co m.equallogic:0-8a0906-e6b70e107-e87000e7acf4d4e5-lieven-winxp-r17453,if=ide,boot=on,cache=none,aio=native -m 1024 -monitor tcp:0:4001,server,nowait -vnc :1 -name 'lieven-winxp-te st' -boot order=c,menu=on -k de -pidfile /var/run/qemu/vm-265.pid -mem-path /hugepages -mem-prealloc -cpu qemu64,model_id='Intel(R) Xeon(R) CPU E5640 @ 2.67GHz',-n 
x -rtc base=localtime,clock=vm -vga cirrus -usb -usbdevice tablet
Starting program: /usr/local/bin/qemu-system-x86_64 -net tap,vlan=141,script=no,downscript=no,ifname=tap0 -net nic,vlan=141,model=rtl8139,macaddr=52:54:00:ff:00:93 -drive format =host_device,file=/dev/mapper/iqn.2001-05.com.equallogic:0-8a0906-e6b70e107-e87000e7acf4d4e5-lieven-winxp-r17453,if=ide,boot=on,cache=none,aio=native -m 1024 -monitor tcp:0:4001, server,nowait -vnc :1 -name 'lieven-winxp-test' -boot order=c,menu=on -k de -pidfile /var/run/qemu/vm-265.pid -mem-path /hugepages -mem-prealloc -cpu qemu64,model_id='Intel(R ) Xeon(R) CPU E5640 @ 2.67GHz',-nx -rtc base=localtime,clock=vm -vga cirrus -usb -usbdevice tablet 
[Thread debugging using libthread_db enabled]

[New Thread 0x7ffff694e700 (LWP 29042)]
[New Thread 0x7ffff6020700 (LWP 29043)]
[New Thread 0x7ffff581f700 (LWP 29074)]
[Thread 0x7ffff581f700 (LWP 29074) exited]
[New Thread 0x7ffff581f700 (LWP 29124)]
[Thread 0x7ffff581f700 (LWP 29124) exited]
[New Thread 0x7ffff581f700 (LWP 29170)]
[Thread 0x7ffff581f700 (LWP 29170) exited]
[New Thread 0x7ffff581f700 (LWP 29246)]
[Thread 0x7ffff581f700 (LWP 29246) exited]
[New Thread 0x7ffff581f700 (LWP 29303)]
[Thread 0x7ffff581f700 (LWP 29303) exited]
[New Thread 0x7ffff581f700 (LWP 29349)]
[Thread 0x7ffff581f700 (LWP 29349) exited]
[New Thread 0x7ffff581f700 (LWP 29399)]
[Thread 0x7ffff581f700 (LWP 29399) exited]
[New Thread 0x7ffff581f700 (LWP 29471)]
[Thread 0x7ffff581f700 (LWP 29471) exited]
[New Thread 0x7ffff581f700 (LWP 29521)]
[Thread 0x7ffff581f700 (LWP 29521) exited]
[New Thread 0x7ffff581f700 (LWP 29593)]
[Thread 0x7ffff581f700 (LWP 29593) exited]
[New Thread 0x7ffff581f700 (LWP 29703)]
[Thread 0x7ffff581f700 (LWP 29703) exited]

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb)

(gdb) thread apply all bt full

Thread 3 (Thread 0x7ffff6020700 (LWP 29043)):
#0 0x00007ffff79c385c in pthread_cond_wait@@GLIBC_2.3.2 ()
from /lib/libpthread.so.0
No symbol table info available.
#1 0x00000000004d3ae1 in qemu_cond_wait (cond=0x1612d50, mutex=0x1612d80) 
at qemu-thread.c:133
err = 0
__func__ = "qemu_cond_wait"
#2 0x00000000004d2b39 in vnc_worker_thread_loop (queue=0x1612d50)
at ui/vnc-jobs-async.c:198
job = 0x7ffff058cd20
entry = 0x0
tmp = 0x0
vs = {csock = -1, ds = 0x15cb380, dirty = {{0, 0, 0, 0,
0} <repeats 2048 times>}, vd = 0x1607ff0, need_update = 0,
force_update = 0, features = 243, absolute = 0, last_x = 0,
last_y = 0, client_width = 0, client_height = 0, vnc_encoding = 7,
major = 0, minor = 0, challenge = '\000' <repeats 15 times>,
info = 0x0, output = {capacity = 3194, offset = 2723,
buffer = 0x1fbbfd0 ""}, input = {capacity = 0, offset = 0,
buffer = 0x0}, write_pixels = 0x4c4bc9 <vnc_write_pixels_generic>,
clientds = {flags = 0 '\000', width = 720, height = 400,
linesize = 2880,
data = 0x7ffff6021010 <Address 0x7ffff6021010 out of bounds>,
pf = {bits_per_pixel = 32 ' ', bytes_per_pixel = 4 '\004',
depth = 24 '\030', rmask = 0, gmask = 0, bmask = 0, amask = 0,
rshift = 16 '\020', gshift = 8 '\b', bshift = 0 '\000',
ashift = 24 '\030', rmax = 255 '\377', gmax = 255 '\377',
bmax = 255 '\377', amax = 255 '\377', rbits = 8 '\b',
gbits = 8 '\b', bbits = 8 '\b', abits = 8 '\b'}},
audio_cap = 0x0, as = {freq = 0, nchannels = 0, fmt = AUD_FMT_U8,
endianness = 0}, read_handler = 0, read_handler_expect = 0,
modifiers_state = '\000' <repeats 255 times>, led = 0x0,
abort = false, output_mutex = {lock = {__data = {__lock = 0,
__count = 0, __owner = 0, __nusers = 0, __kind = 0,
__spins = 0, __list = {__prev = 0x0, __next = 0x0}},
__size = '\000' <repeats 39 times>, __align = 0}}, tight = {
type = 7, quality = 255 '\377', compression = 9 '\t',
pixel24 = 1 '\001', tight = {capacity = 3146708, offset = 1376,
buffer = 0x7ffff4684010 ""}, tmp = {capacity = 3194,
offset = 2672, buffer = 0x1fbbfd0 ""}, zlib = {
capacity = 141451, offset = 0,
buffer = 0x1805da0 "B--G\317\253\031=\257f\364\274\232\321\363jF\317\253\241\326y5"}, gradient = {capacity = 0, offset = 0, buffer = 0x0}, 
levels = {9, 9, 9, 0}, stream = {{
next_in = 0x7ffff4684460 "\002\003\002\003\002\002\002\002\002\002\002\002\002", avail_in = 0, total_in = 9048240, next_out = 0x1805df6 "d\276\345c\363\216\237\212\377\314\003\236\246\\$\361\025~\032\311\232\067q&_$\231\251y\262*!\231\067\236\067\363\214\347\315\240\361\221,\274T\257\221\314\333\341\251\362R\373\232_\311a\272\002\061sgt\317\030\332\262~\300\063\267]\307\267\343\033", avail_out = 141365, 
total_out = 1034664, msg = 0x0, state = 0x16ea550,
zalloc = 0x4ca2d8 <vnc_zlib_zalloc>,
zfree = 0x4ca315 <vnc_zlib_zfree>, opaque = 0x7ffff6015920,
data_type = 0, adler = 1285581469, reserved = 0}, {
next_in = 0x7ffff4684022 "\002\002", avail_in = 0,
total_in = 46491,
next_out = 0x1805da8 "\257f\364\274\232\321\363jF\317\253\241\326y5", avail_out = 141443, total_out = 9905, msg = 0x0, state = 0x17a3f00, 
zalloc = 0x4ca2d8 <vnc_zlib_zalloc>,
zfree = 0x4ca315 <vnc_zlib_zfree>, opaque = 0x7ffff6015920,
data_type = 0, adler = 2415253306, reserved = 0}, {
next_in = 0x7ffff4684570 "\017(`", avail_in = 0,
total_in = 2188024,
next_out = 0x1805dbd "z\222\024#\233O\214g\341\352\211/U\310s\017\361\245\020\262\343\211TO\222\371\304\207\fryK|\251E\222\343\311+\237\351`>\355\312sR\265\320\272~\001", avail_out = 141422, total_out = 100512, msg = 0x0, 
state = 0x1682950, zalloc = 0x4ca2d8 <vnc_zlib_zalloc>,
zfree = 0x4ca315 <vnc_zlib_zfree>, opaque = 0x7ffff6015920,
data_type = 0, adler = 3999694267, reserved = 0}, {
next_in = 0x0, avail_in = 0, total_in = 0, next_out = 0x0,
avail_out = 0, total_out = 0, msg = 0x0, state = 0x0,
zalloc = 0, zfree = 0, opaque = 0x0, data_type = 0, adler = 0,
reserved = 0}}}, zlib = {zlib = {capacity = 0, offset = 0,
buffer = 0x0}, tmp = {capacity = 0, offset = 0, buffer = 0x0},
stream = {next_in = 0x0, avail_in = 0, total_in = 0,
next_out = 0x0, avail_out = 0, total_out = 0, msg = 0x0,
state = 0x0, zalloc = 0, zfree = 0, opaque = 0x0, data_type = 0,
adler = 0, reserved = 0}, level = 0}, hextile = {
send_tile = 0x4cd21d <send_hextile_tile_generic_32>},
mouse_mode_notifier = {notify = 0x80, node = {tqe_next = 0x1612da8,
tqe_prev = 0x7ffff6020700}}, next = {tqe_next = 0x7ffff6020700,
tqe_prev = 0x7ffff7ffe128}}
n_rectangles = 40
saved_offset = 2
flush = true
#3 0x00000000004d302c in vnc_worker_thread (arg=0x1612d50)
at ui/vnc-jobs-async.c:302
queue = 0x1612d50
#4 0x00007ffff79be9ca in start_thread () from /lib/libpthread.so.0
No symbol table info available.
#5 0x00007ffff6c3970d in clone () from /lib/libc.so.6
No symbol table info available.
#6 0x0000000000000000 in ?? ()
No symbol table info available.

Thread 2 (Thread 0x7ffff694e700 (LWP 29042)):
#0 0x00007ffff6c31197 in ioctl () from /lib/libc.so.6
No symbol table info available.
#1 0x0000000000434c12 in kvm_run (env=0x118c2e0)
at /usr/src/qemu-kvm-0.14.0/qemu-kvm.c:582
r = 0
kvm = 0x1172538
run = 0x7ffff7fc7000
fd = 15
#2 0x0000000000435ed4 in kvm_cpu_exec (env=0x118c2e0)
at /usr/src/qemu-kvm-0.14.0/qemu-kvm.c:1233
r = 0
#3 0x00000000004364f7 in kvm_main_loop_cpu (env=0x118c2e0)
at /usr/src/qemu-kvm-0.14.0/qemu-kvm.c:1419
run_cpu = 1
#4 0x0000000000436640 in ap_main_loop (_env=0x118c2e0)
at /usr/src/qemu-kvm-0.14.0/qemu-kvm.c:1466
env = 0x118c2e0
signals = {__val = {18446744067267100671,
18446744073709551615 <repeats 15 times>}}
data = 0x0
#5 0x00007ffff79be9ca in start_thread () from /lib/libpthread.so.0
No symbol table info available.
#6 0x00007ffff6c3970d in clone () from /lib/libc.so.6
No symbol table info available.
#7 0x0000000000000000 in ?? ()
No symbol table info available.

Thread 1 (Thread 0x7ffff7ff0700 (LWP 29038)):
#0 0x0000000000000000 in ?? ()
No symbol table info available.
#1 0x000000000041d669 in main_loop_wait (nonblocking=0)
at /usr/src/qemu-kvm-0.14.0/vl.c:1388
pioh = 0x1652870
ioh = 0x1613330
rfds = {fds_bits = {0 <repeats 16 times>}}
wfds = {fds_bits = {1048576, 0 <repeats 15 times>}}
xfds = {fds_bits = {0 <repeats 16 times>}}
ret = 1
nfds = 21
tv = {tv_sec = 0, tv_usec = 999998}
timeout = 1000
#2 0x0000000000436a4a in kvm_main_loop ()
at /usr/src/qemu-kvm-0.14.0/qemu-kvm.c:1589
mask = {__val = {268443712, 0 <repeats 15 times>}}
sigfd = 19
#3 0x000000000041d785 in main_loop () at /usr/src/qemu-kvm-0.14.0/vl.c:1429 
r = 0
#4 0x000000000042166a in main (argc=33, argv=0x7fffffffe658,
envp=0x7fffffffe768) at /usr/src/qemu-kvm-0.14.0/vl.c:3201
gdbstub_dev = 0x0
i = 64
snapshot = 0
linux_boot = 0
icount_option = 0x0
initrd_filename = 0x0
kernel_filename = 0x0
kernel_cmdline = 0x5e57a3 ""
boot_devices = "c\000d", '\000' <repeats 29 times>
ds = 0x15cb380
dcl = 0x0
cyls = 0
heads = 0
secs = 0
translation = 0
hda_opts = 0x0
opts = 0x1171a80
olist = 0x7fffffffe3f0
optind = 33
optarg = 0x7fffffffebce "tablet"
loadvm = 0x0
machine = 0x962cc0
cpu_model = 0x7fffffffeb51 "qemu64,model_id=Intel(R) Xeon(R) CPU", ' ' <repeats 11 times>, "E5640 @ 2.67GHz,-nx" 
tb_size = 0
pid_file = 0x7fffffffeb10 "/var/run/qemu/vm-265.pid"
incoming = 0x0
show_vnc_port = 0
defconfig = 1
(gdb) info threads
3 Thread 0x7ffff6020700 (LWP 29043) 0x00007ffff79c385c in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/libpthread.so.0 
2 Thread 0x7ffff694e700 (LWP 29042) 0x00007ffff6c31197 in ioctl ()
from /lib/libc.so.6
* 1 Thread 0x7ffff7ff0700 (LWP 29038) 0x0000000000000000 in ?? ()
(gdb)


Help appreciated!

Thanks,
Peter


Hi Peter,

did you apply this patch which fixes one of the known vnc problems
(but is still missing in qemu git master):

http://lists.nongnu.org/archive/html/qemu-devel/2011-03/msg00256.html

Then you can read this thread:

http://lists.nongnu.org/archive/html/qemu-devel/2011-03/msg00313.html

And finally the following modifications of ui/vnc.c might help to see
whether you experience the same kind of crash as I get here in
my environment. They add assertions for bad memory access
which occurs sometimes when a vnc client-server connection exists and
the screen is refreshed after a resolution change.
The code line with the //~ comment also includes a fix which
works for me.

Regards,
Stefan W.
@@ -2382,6 +2384,10 @@ static int vnc_refresh_server_surface(VncDisplay *vd) 
     int y;
     uint8_t *guest_row;
     uint8_t *server_row;
+
+    size_t guest_size = vd->guest.ds->linesize * vd->guest.ds->height;
+    size_t server_size = vd->server->linesize * vd->server->height;
+
     int cmp_bytes;
     VncState *vs;
     int has_dirty = 0;
@@ -2399,11 +2405,15 @@ static int vnc_refresh_server_surface(VncDisplay *vd) 
      * Update server dirty map.
      */
     cmp_bytes = 16 * ds_get_bytes_per_pixel(vd->ds);
+    if (cmp_bytes > vd->ds->surface->linesize) {
+        //~ fix crash: cmp_bytes = vd->ds->surface->linesize;
+    }


Stefan, I can confirm that I ran into issues if this is check is missing:
qemu-kvm-0.14.0: ui/vnc.c:2292: vnc_refresh_server_surface: Assertion `cmp_bytes <= vd->ds->surface->linesize' failed.
Somebody should definetly look into the root cause or at least your proposed check+fix should be added. 

Peter



Hi Peter,

I just sent the patch which limits cmp_bytes to qemu-devel
(two mails: for stable-0.14 and for master).

The bug is triggered by certain strange screen resolutions,
for example while booting MIPS Malta with a Debian Linux kernel.

Regards,
Stefan
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