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

[Peter Lieven <pl@dlh.net>]

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