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[Qemu-devel] [Bug 1617929] Re: qemu hangs in pselect syscall

From: Peter Maydell
Subject: [Qemu-devel] [Bug 1617929] Re: qemu hangs in pselect syscall
Date: Mon, 06 Nov 2017 17:03:16 -0000

I can't reproduce this with current git master, and I know we fixed a
lot of race conditions in linux-user. So I'm going to close this bug --
if it's still a problem for you with new QEMU, please reopen, preferably
with a repro case that's more frequent than 1-in-50-or-less.

** Changed in: qemu
       Status: New => Fix Committed

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  qemu hangs in pselect syscall

Status in QEMU:
  Fix Committed

Bug description:
  I'm using git commit d75aa4372f0414c9960534026a562b0302fcff29 (v2.7.0-rc4) 
configured with;
      --enable-linux-user \
      --disable-system \
      --disable-tools \
      --disable-guest-agent \
      --static --disable-linux-aio \
      --disable-fdt \
      --without-pixman \
      --disable-blobs \
  Stable version (v2.6.0) also have the same problem.

  In a chroot environment I ran below command-line to compile some things, 
different sources each time.
      /usr/bin/qemu-arm -0 /usr/bin/edje_cc /usr/bin/edje_cc -id 

  Here is back trace with gdb;
  #0  safe_syscall_end () at 
  #1  0x60049370 in safe_pselect6 (nfds=10, readfds=0xffa31b5c, 
writefds=0xffa31bdc, exceptfds=0xffa31c5c, timeout=0x0, sig=0x0)
      at /usr/src/debug/qemu-2.6.94/linux-user/syscall.c:855
  #2  0x6004b2fe in do_select (n=10, rfd_addr=1082122232, wfd_addr=1082122360, 
efd_addr=1082122488, target_tv_addr=0)
      at /usr/src/debug/qemu-2.6.94/linux-user/syscall.c:1386
  #3  0x6005e5ba in do_syscall (cpu_env=0x640d0454, num=142, arg1=10, 
arg2=1082122232, arg3=1082122360, arg4=1082122488, arg5=0, arg6=1087473216, 
      arg8=0) at /usr/src/debug/qemu-2.6.94/linux-user/syscall.c:9690
  #4  0x60045def in cpu_loop (env=0x640d0454) at 
  #5  0x60047640 in main (argc=10, argv=0xffa33c84, envp=0xffa33cb0) at 

  Attached core file taken from gdb. To see the stack frame, you could try; 
  $ tar -xf reproduced_118_04.tar.bz2; gdb --core core.1823 qemu-arm

  And recent strace log for PID 1823(stucked one);
  79965 [  313s] 1823 :0x8e _newselect(10,[9,3,],[],[],NULL)
  79966 [  313s]  ==>[pselect6(0xa)=]
  79967 [  313s]  [pselect6=0x1]<==
  79968 [  313s] 1823 :0x8e _newselect(10,[9,],[],[],NULL)
  79969 [  313s] 1823 :0x8e =>  = 0x00000001 ([9,],[],[],NULL)
  79970 [  313s] 1823 :0xfc epoll_wait(3,1082121456,32,0,1082121456,3)
  79971 [  313s] 1823 :0xfc epoll_wait(3,1082121456,32,0,1082121456,3)
  79972 [  313s] 1823 :0xfc =>  = 0
  79973 [  313s] 1823 :0x3 read(9,0x407fdeec,16)
  79974 [  313s] 1823 :0x3 read(9,0x407fdeec,16)
  79975 [  313s] 1823 :0x3 =>  = 8
  79976 [  313s] 1823 :0x107 
  79977 [  313s] 1823 :0x107 
  79978 [  313s] 1823 :0x107 =>  = 0
  79979 [  313s] 1823 :0x8e _newselect(10,[9,3,],[],[],NULL)
  79980 [  313s]  ==>[pselect6(0xa)=]

  I'm using 64-bit Ubuntu with kernel release Linux 3.19.0-25-generic 
  Reproducibility is low. One occurrence out of 50+ trials.

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