Messages in this thread |  | | Date | Thu, 23 Oct 2014 13:03:46 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 4/6] SRCU free VMAs |
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On Thu, Oct 23, 2014 at 06:14:45PM +0800, Lai Jiangshan wrote: > > > > > +struct vm_area_struct *find_vma_srcu(struct mm_struct *mm, unsigned long addr) > > +{ > > + struct vm_area_struct *vma; > > + unsigned int seq; > > + > > + WARN_ON_ONCE(!srcu_read_lock_held(&vma_srcu)); > > + > > + do { > > + seq = read_seqbegin(&mm->mm_seq); > > + vma = __find_vma(mm, addr); > > will the __find_vma() loops for ever due to the rotations in the RBtree?
No, a rotation takes a tree and generates a tree, furthermore the rotation has a fairly strict fwd progress guarantee seeing how its now done with preemption disabled.
Therefore, even if we're in a node that's being rotated up, we can only 'loop' for as long as it takes for the new pointer stores to become visible on our CPU.
Thus we have a tree descent termination guarantee.
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