Messages in this thread | | | Date | Thu, 12 Sep 2013 17:56:08 -0700 | Subject | Re: linux-next: manual merge of the akpm tree with Linus' tree | From | Linus Torvalds <> |
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On Tue, Sep 10, 2013 at 4:37 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > From a quick look, this looks pretty broken: > > if (list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru)) > this_cpu_inc(nr_dentry_unused); > dentry->d_flags |= DCACHE_LRU_LIST; > > because if that list_lru_add() can fail, then we shouldn't set the > DCACHE_LRU_LIST bit either. > > That said, I don't see how it can fail. We only do this with the > dentry locked, and when it's not already on the LRU list. So I think > the "if()" is just misleading and unnecessary - but the code works.
So I thought you'd clean this up. Looking again, it still seems really confused, and I'm finding actual bugs.
You don't clear the DCACHE_LRU_LIST when you remove dentries from the d_lru list. In other cases (like shrink_dentry_list), you clear just the DCACHE_SHRINK_LIST.
As a result, the "if ()" isn't necessarily unnecessary, but there are actual bugs. It looks like the dentry can be removed from the d_lru lists without the bit ever getting cleared, and if that happens, it will never be moved back.
The rule for DCACHE_LRU_LIST was - and should be - that the bit is set IFF the d_lru list is not empty. So it gets set when a dentry is moved to the LRU lists, but it _stays_ set if the dentry is moved to the shrink_list. It then gets cleared when the dentry is removed from any d_lru list (ie "list_del_init()").
I'll walk through the code, it looked suspicious. Maybe there's something subtle that makes it work, but I don't see it.
Linus
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