Messages in this thread |  | | From | Rusty Russell <> | Subject | Re: [PATCH 1 of 9] Lock the entire mm to prevent any mmu related operation to happen | Date | Tue, 22 Apr 2008 15:06:24 +1000 |
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On Wednesday 09 April 2008 01:44:04 Andrea Arcangeli wrote: > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1050,6 +1050,15 @@ > unsigned long addr, unsigned long len, > unsigned long flags, struct page **pages); > > +struct mm_lock_data { > + spinlock_t **i_mmap_locks; > + spinlock_t **anon_vma_locks; > + unsigned long nr_i_mmap_locks; > + unsigned long nr_anon_vma_locks; > +}; > +extern struct mm_lock_data *mm_lock(struct mm_struct * mm); > +extern void mm_unlock(struct mm_struct *mm, struct mm_lock_data *data);
As far as I can tell you don't actually need to expose this struct at all?
> + data->i_mmap_locks = vmalloc(nr_i_mmap_locks * > + sizeof(spinlock_t));
This is why non-typesafe allocators suck. You want 'sizeof(spinlock_t *)' here.
> + data->anon_vma_locks = vmalloc(nr_anon_vma_locks * > + sizeof(spinlock_t));
and here.
> + err = -EINTR; > + i_mmap_lock_last = NULL; > + nr_i_mmap_locks = 0; > + for (;;) { > + spinlock_t *i_mmap_lock = (spinlock_t *) -1UL; > + for (vma = mm->mmap; vma; vma = vma->vm_next) { ... > + data->i_mmap_locks[nr_i_mmap_locks++] = i_mmap_lock; > + } > + data->nr_i_mmap_locks = nr_i_mmap_locks;
How about you track your running counter in data->nr_i_mmap_locks, leave nr_i_mmap_locks alone, and BUG_ON(data->nr_i_mmap_locks != nr_i_mmap_locks)?
Even nicer would be to wrap this in a "get_sorted_mmap_locks()" function.
Similarly for anon_vma locks.
Unfortunately, I just don't think we can fail locking like this. In your next patch unregistering a notifier can fail because of it: that not usable.
I think it means you need to add a linked list element to the vma for the CONFIG_MMU_NOTIFIER case. Or track the max number of vmas for any mm, and keep a pool to handle mm_lock for this number (ie. if you can't enlarge the pool, fail the vma allocation).
Both have their problems though... Rusty.
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