On Thu, 2011-11-24 at 08:16 -0500, John David Anglin wrote: > As GCC has gotten larger with time, I started seeing hangs in the > stage1 compilers when they are compiled > with no optimization. This first was seen with gnat1. I now see it > with cc1 and cc1plus. > > The hangs always occur at the same place (ldw,s instruction) in the > GCC casesi insn pattern: > > (gdb) disass $pc-16,$pc+16 > Dump of assembler code from 0x45fbec4 to 0x45fbee4: > 0x045fbec4 <cpp_spell_token+68>: ldw 0(ret0),ret0 > 0x045fbec8 <cpp_spell_token+72>: cmpib,<<,n 3,ret0,0x45fc168 > <cpp_spell_token+744> > 0x045fbecc <cpp_spell_token+76>: ldil L%45fb800,r19 > 0x045fbed0 <cpp_spell_token+80>: ldo 6dc(r19),r19 > => 0x045fbed4 <cpp_spell_token+84>: ldw,s ret0(r19),r19 > 0x045fbed8 <cpp_spell_token+88>: bv,n r0(r19) > 0x045fbedc <cpp_spell_token+92>: # 45fbeec > 0x045fbee0 <cpp_spell_token+96>: # 45fbfc8 > > What is interesting about this instruction is that it usually involves > an I and D access to the same page. > strace shows nothing for process. gdb can't single step from the > instruction. A break at the next > instruction is never hit. > > I see the following with sysrq-trigger: > > cc1plus R running task 0 16932 16931 0x00000010 > Backtrace: > timer_interrupt(CPU 1): delayed! cycles 77ED56D2 rem BD46F next/now > 411D1E1AE13C/411D1E0F0CCD > > Note the delayed timer interrupt "always" seems to occur. Also, see > that the program isn't running kernel > code. > > So, my theory is there is a bug in the TLB miss handling. Somehow a > data miss ejects the instruction entry, > and we get into a loop inserting I and D TLB entries. Sometimes the > machine gets out of the loop but it takes > hours. I'm still a bit Jetlagged from a customer trip to Germany, but this looks entirely possible: Appendix F says that a later TLB insertion purges an earlier one, so I'd say in a combined I/D TLB inserting consecutive I and D entries purges the I. It looks like a fix might be to insert TLB entries supporting both data and instruction access in the combined TLB case. James -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
