Re: locking question: do_mmap(), do_munmap()

Ralf Baechle
1999-10-15T17:14:02Z

On Wed, Oct 13, 1999 at 09:32:54AM +0200, Manfred Spraul wrote:

> Kanoj Sarcar wrote:
> > Here's a primitive patch showing the direction I am thinking of. I do not
> > have any problem with a spinning lock, but I coded this against 2.2.10,
> > where insert_vm_struct could go to sleep, hence I had to use sleeping
> > locks to protect the vma chain.
>
> I found a few places where I don't know how to change them.
>
> 1) arch/mips/mm/r4xx0.c:
> their flush_cache_range() function internally calls find_vma().
> flush_cache_range() is called by proc/mem.c, and it seems that this
> function cannot get the mmap semaphore.
> Currently, every caller of flush_cache_range() either owns the kernel
> lock or the mmap_sem.
> OTHO, this function contains a race anyway [src_vma can go away if
> handle_mm_fault() sleeps, src_vma is used at the end of the function.]

The sole reason for fiddling with the VMA is that we try to optimize
icache flushing for non-VM_EXEC vmas. This optimization is broken
as the MIPS hardware doesn't make a difference between read and execute
in page permissions, so the icache might be dirty even though the vma
has no exec permission. So I'll have to re-implement this whole things
anyway. The other problem is an efficience problem. A call like
flush_cache_range(some_mm_ptr, 0, TASK_SIZE) would take a minor eternity
and for MIPS64 a full eternity ...

Ralf