On Mon, 2009-01-05 at 09:07 -0800, Nishanth Aravamudan wrote: > On 05.01.2009 [06:26:55 -0800], mehul vora wrote: > > Nishanth, > > > > I went through "munmap" code and found that core kernel (arch > > independent) code removes all "vma" references of the passed vaddr and > > then it calls arch dependent hooks. MIPS code removes all pagetable > > reference of the passed vaddr and flushes tlbs on all cpus. So after > > munmap returns, if process will try to access the same address again > > then it will receive a SIGSEGV signal. > > We do call it a black hole, as I've said :) It's hairy code. > > > I wrote a simple program (not linked with libhugetlbfs - see > > attachment) to cross check this on MIPS. The moment program does the > > "munmap" of the code segment it immediately receives a SIGSEGV. Same > > program also crashes on x86 with SIGSEGV. > > Right, I see that. > > > Is this program, at a high level, very similar to libhugetlb init > > (constructor - munmap/mmap sequence) code ? If yes, then, Is there > > anything specific libhugetlbfs does before unmapping the code segment > > apart from copying all segments in to hugepages to make this work ? > > A few thoughts: we don't unmap all segments, only those that need to be > remapped. Not sure if that matters. The only external reference we > resolve between unmapping and mapping is mmap(), which is why we have > that false mmap() call. So, nothing else should access the text segment > between unmap and map in libhugetlbfs. I know libhugetlbfs works on x86 > :) I'll think about it further. Maybe someone else will have some ideas.
You are not allowed to call libc functions while segments are unmapped. Calling printf (for example) will cause a lookup of the symbol stdout and may trigger dynamic symbol lookups. ------------------------------------------------------------------------------ _______________________________________________ Libhugetlbfs-devel mailing list Libhugetlbfs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libhugetlbfs-devel
