Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 9 Jan 2012 11:18:13 -0800 | Subject | Re: [RFC PATCH] shrink_dcache_parent() deadlock |
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On Mon, Jan 9, 2012 at 11:04 AM, Christoph Hellwig <hch@infradead.org> wrote: > > After Dave's patch select_parent isolates dentries that are going to > be dropped directly to an on-stack list instead of abusing the LRU. > > With that scheme the trylock and retry loop in __shrink_dcache_sb > goes away completely for this caller.
Yes, but it still exists for the prune_dcache_sb() case.
So prune_dcache_sb() puts random dentries on its own private lists, and drops the lru_lock (and the dentry lock).
In the meantime, what protects us from select_parent() finding those *same* dentries, and doing
dentry_lru_move_list(dentry, dispose);
which - despite the name - moves the dentry not from the lru list, but from the prune_dcache_sb local list to the select_parent() local list..
Hmm. I guess the endless "move back-and-forth" thing is gone, but the random "move from one private list to another" makes me worry about the confusion.
But I guess we don't care - the same thing is going to happen to the dentry regardless of which of the local lists it is on.
And in any case, I think Dave's patch looks like a nice cleanup. Does it work for people in that forward-ported-alone version I sent out?
And Miklos, does it fix your test-case? Because if so, I think Dave's patch is nicer, and avoids adding a new state bit by just cleaning things up in general.
Linus
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