Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 26 Apr 2010 11:53:47 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [BUGFIX][mm][PATCH] fix migration race in rmap_walk |
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On Mon, 26 Apr 2010 08:49:01 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Sat, 24 Apr 2010 11:43:24 +0100 > Mel Gorman <mel@csn.ul.ie> wrote:
> > It looks nice but it still broke after 28 hours of running. The > > seq-counter is still insufficient to catch all changes that are made to > > the list. I'm beginning to wonder if a) this really can be fully safely > > locked with the anon_vma changes and b) if it has to be a spinlock to > > catch the majority of cases but still a lazy cleanup if there happens to > > be a race. It's unsatisfactory and I'm expecting I'll either have some > > insight to the new anon_vma changes that allow it to be locked or Rik > > knows how to restore the original behaviour which as Andrea pointed out > > was safe. > > > Ouch. Hmm, how about the race in fork() I pointed out ? > Forget this. Sorry for noise.
== This is a memo for myself.
*) at fork, when copying a vma for file, vma_prio_tree_add() is called before copying page tables. There are several patterns.
Assume tasks named as t1,t2,t3,t4,t5 and their own vmas v1,v2,v3,v4,v5 which map a range in address spaces.
(a) t1 forks t2. v1 is in prio_tree, v2 for t2 will be pointed by ->head pointer.
\ v1 --(head)---> v2 / \ ? ?
vma_prio_tree_foreach() order : v1->v2.
(b) after (a), t2 forks t3. (list_add() is used.)
\ v1 --(head)--> v2 ->(list.next)->v3 / \ ? ?
vma_prio_tree_foreach() order : v1->v2->v3
(c) after (b), t1 forks t4.
\ v1 --(head)--> v2 ->(list.next)->v3->v4 / \ ? ?
vma_prio_tree_foreach() order : v1->v2->v3->v4
(d) after (c), t4 forks t5.
\ v1 --(head)--> v2 ->(list.next)->v3->v4->v5 / \ ? ? vma_prio_tree_foreach() order : v1->v2->v3->v4->v5
(e) after (c), t3 forks t5. \ v1 --(head)--> v2 ->(list.next)->v3->v5->v4- / \ ? ? vma_prio_tree_foreach() order : v1->v2->v3->v5->v4
.....in any case, it seems vma_prio_tree_foreach() finds the parent's vma 1st.
Thx, -Kame
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