On an 8GB dual cpu opteron (Tyan S2884) 2.6.10 kernel I can reproduce a crash within
several minutes by creating/mapping/deleting/unmapping 512MB files using the
code below. On a IA32 box (Xeon 2.4GHz, 3GB SuperMicro X5DA8) the crash is
fatal (no /var/log/messages) and immediate. Executables for x86_64 and i386
from either FC3 or Redhat ES3.0 available on request. GCC is 3.4.2 on both
machines and O/S releases.


Feb  2 11:28:49 noreaster kernel: ----------- [cut here ] --------- [please bite here ] ---------
Feb  2 11:28:49 noreaster kernel: Kernel BUG at hugetlbpage:212
Feb  2 11:28:49 noreaster kernel: invalid operand: 0000 [1] SMP
Feb  2 11:28:49 noreaster kernel: CPU 1
Feb  2 11:28:49 noreaster kernel: Modules linked in:
Feb  2 11:28:49 noreaster kernel: Pid: 15687, comm: DssiEPSearch Not tainted 2.6.10
Feb  2 11:28:49 noreaster kernel: RIP: 0010:[<ffffffff8011e3cb>] <ffffffff8011e3cb>{unmap_hugepage_range+75}
Feb  2 11:28:49 noreaster kernel: RSP: 0018:00000100d7701dd8  EFLAGS: 00010206
Feb  2 11:28:49 noreaster kernel: RAX: 000001012eee98e0 RBX: 000001001000a0c0 RCX: 0000000061001000
Feb  2 11:28:49 noreaster kernel: RDX: 0000000061001000 RSI: 0000000041000000 RDI: 000001012eee98e0
Feb  2 11:28:49 noreaster kernel: RBP: 0000000041000000 R08: 0000000061200000 R09: 00000100d7701f10
Feb  2 11:28:49 noreaster kernel: R10: 0000000000000000 R11: 0000000000000202 R12: 0000000061001000
Feb  2 11:28:49 noreaster kernel: R13: 00000101f6ee0040 R14: 0000000041000000 R15: 000001012eee98e0
Feb  2 11:28:49 noreaster kernel: FS:  0000002a96b88080(0000) GS:ffffffff80611c00(0000) knlGS:0000000000000000
Feb  2 11:28:49 noreaster kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
Feb  2 11:28:49 noreaster kernel: CR2: 0000002a9632e970 CR3: 000000001184a000 CR4: 00000000000006e0
Feb  2 11:28:49 noreaster kernel: Process DssiEPSearch (pid: 15687, threadinfo 00000100d7700000, task 00000101215c63f0)
Feb  2 11:28:49 noreaster kernel: Stack: 0000000000000206 000001001000a0c0 0000000041000000 000001012eee9838
Feb  2 11:28:49 noreaster kernel:        00000101f6ee0040 0000000061200000 000001012eee98e0 ffffffff8015d800
Feb  2 11:28:49 noreaster kernel:        0000000000000000 ffffffff802bf59b
Feb  2 11:28:49 noreaster kernel: Call Trace:<ffffffff8015d800>{unmap_vmas+320} <ffffffff802bf59b>{fpga_ioctl+2171}
Feb  2 11:28:49 noreaster kernel:        <ffffffff802c141b>{fpga_read+555} <ffffffff80161a23>{do_munmap+547}
Feb  2 11:28:49 noreaster kernel:        <ffffffff801627a8>{sys_munmap+72} <ffffffff8010d216>{system_call+126}
Feb  2 11:28:49 noreaster kernel:
Feb  2 11:28:49 noreaster kernel:
Feb  2 11:28:49 noreaster kernel: Code: 0f 0b 33 1f 49 80 ff ff ff ff d4 00 4c 89 f5 4d 39 e6 66 66
Feb  2 11:28:49 noreaster kernel: RIP <ffffffff8011e3cb>{unmap_hugepage_range+75} RSP <00000100d7701dd8>
Feb  2 11:32:32 noreaster kernel: Linux version 2.6.10 (root@noreaster) (gcc version 3.4.2) #47 SMP Wed Feb 2 08:01:40 CST 2005

// code to access a huge tlb filesystem

#if defined(__linux__) && defined(__x86_64__)
   HugePageFileName_ = new char[64];
   ::sprintf(HugePageFileName_, "/mnt/huge/Silo_XXXXXX");
   ::mkstemp(HugePageFileName_);			// randomize this name
   Mmap_Fd_ = ::open(HugePageFileName_, O_CREAT | O_RDWR | O_LARGEFILE | O_TRUNC, 0755);
   if (Mmap_Fd_ != -1)
   {
      LONG64 MyBig = Big * sizeof(LONG64) + ((2UL * 1024UL * 1024UL) - 1);
      MyBig &= ~((2UL * 1024UL * 1024UL) - 1);
      BigBlock0_ = (LONG64 *) ::mmap(NULL, MyBig, 
      		(PROT_READ | PROT_WRITE), 
      		MAP_SHARED, Mmap_Fd_, 0);
      if (BigBlock0_ == MAP_FAILED || !BigBlock0_)
      {
         ::perror("mmap failed for huge pages");
	 ::cerr << "Asked for ";
	 printHRNumber(MyBig, cerr);
	 ::cerr << endl;
	 ::close(Mmap_Fd_);
	 ::unlink(HugePageFileName_);
	 delete [] HugePageFileName_;
	 HugePageFileName_ = NULL;
	 Mmap_Fd_ = -1;
	 BigBlock0_ = NULL;
	 BigBlock_ = NULL;
      }
      else
      {
      BigBlock_ = BigBlock0_;
      BigSize_ = MyBig;			// remember this size
      ::unlink(HugePageFileName_);	// pre-delete this file so segfaults
      					// do not leave huge pages tied up.
      }
   }
   else
   {
      if (Debug_)
      {
         ::perror("Sorry, no HUGE pages today");
      }
   }
#endif

// snip from /etc/rc.local

#
# setup the huge file system space pages are 2MB each
#
if [-f /proc/fpga0]; then
   echo "Allocating huge file system"
   echo 1536 > /proc/sys/vm/nr_hugepages
   mount none /mnt/huge -t hugetlbfs -o size=3G,mode=0777
   fi