From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: linux-next: manual merge of the akpm tree with Linus' tree Date: Thu, 12 Sep 2013 17:56:08 -0700 Message-ID: References: <20130910143807.4c32d548e08d2184061f52cb@canb.auug.org.au> <20130910152753.662599171456233c5f91edb4@linux-foundation.org> <20130910222924.GB13318@ZenIV.linux.org.uk> <20130910153520.14e49cd32feb16d45eb8abac@linux-foundation.org> <20130910223624.GC13318@ZenIV.linux.org.uk> <20130910154116.cc4afe048213a779040ea3cc@linux-foundation.org> <20130910224823.GE13318@ZenIV.linux.org.uk> <20130910225934.GF13318@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Al Viro Cc: Andrew Morton , Stephen Rothwell , linux-next , Linux Kernel Mailing List , Dave Chinner , Glauber Costa List-Id: linux-next.vger.kernel.org On Tue, Sep 10, 2013 at 4:37 PM, Linus Torvalds 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