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Date: Mon, 23 Feb 2009 14:58:28 +0900 From: Daisuke Nishimura <nishimura@....nes.nec.co.jp> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>, "balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>, "lizf@...fujitsu.com" <lizf@...fujitsu.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, nishimura@....nes.nec.co.jp Subject: Re: [RFC][PATCH] Reduce size of swap_cgroup by CSS ID v2 I'm sorry for my late reply. It looks good basically, but I have 1 comment. > static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page) > { > - struct mem_cgroup *mem; > + unsigned short id; > + struct mem_cgroup *mem = NULL; > swp_entry_t ent; > > if (!PageSwapCache(page)) > return NULL; > > ent.val = page_private(page); > - mem = lookup_swap_cgroup(ent); > - if (!mem) > - return NULL; > + id = lookup_swap_cgroup(ent); > + rcu_read_lock(); > + mem = mem_cgroup_lookup(id); > if (!css_tryget(&mem->css)) We should check whether "mem" is NULL or not before css_tryget, because "mem" can be NULL(or "id" can be 0) if the page is on swapcache, that is, remove_from_swap_cache has not been called yet. Actually, I got NULL pointer dereference bug here. > - return NULL; > + mem = NULL; > + rcu_read_unlock(); > return mem; > } > Thanks, Daisuke Nishimura. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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