From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f54.google.com (mail-pa0-f54.google.com [209.85.220.54]) by kanga.kvack.org (Postfix) with ESMTP id B85A26B0035 for ; Thu, 30 Jan 2014 16:29:42 -0500 (EST) Received: by mail-pa0-f54.google.com with SMTP id fa1so3637027pad.13 for ; Thu, 30 Jan 2014 13:29:42 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id tq5si7914079pac.211.2014.01.30.13.29.41 for ; Thu, 30 Jan 2014 13:29:41 -0800 (PST) Date: Thu, 30 Jan 2014 13:29:39 -0800 From: Andrew Morton Subject: Re: [PATCH] memcg: fix mutex not unlocked on memcg_create_kmem_cache fail path Message-Id: <20140130132939.96a25a37016a12f9a0093a90@linux-foundation.org> In-Reply-To: References: <1391097693-31401-1-git-send-email-vdavydov@parallels.com> <20140130130129.6f8bd7fd9da55d17a9338443@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Vladimir Davydov , mhocko@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, 30 Jan 2014 13:14:46 -0800 (PST) David Rientjes wrote: > On Thu, 30 Jan 2014, Andrew Morton wrote: > > > Well gee, how did that one get through? > > > > What was the point in permanently allocating tmp_name, btw? "This > > static temporary buffer is used to prevent from pointless shortliving > > allocation"? That's daft - memcg_create_kmem_cache() is not a fastpath > > and there are a million places in the kernel where we could permanently > > leak memory because it is "pointless" to allocate on demand. > > > > The allocation of PATH_MAX bytes is unfortunate - kasprintf() wouild > > work well here, but cgroup_name()'s need for rcu_read_lock() screws us > > up. > > > > What's funnier is that tmp_name isn't required at all since > kmem_cache_create_memcg() is just going to do a kstrdup() on it anyway, so > you could easily just pass in the pointer to memory that has been > allocated for s->name rather than allocating memory twice. We need a buffer to sprintf() into. > > --- a/mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks > > +++ a/mm/memcontrol.c > > @@ -3401,17 +3401,14 @@ static struct kmem_cache *memcg_create_k > > struct kmem_cache *s) > > { > > struct kmem_cache *new = NULL; > > - static char *tmp_name = NULL; > > + static char *tmp_name; > > You're keeping it static and the mutex so you're still keeping it global, > ok... oop, I forgot to remove the `static'. And I suppose the mutex now doesn't do anything, so... From: Andrew Morton Subject: mm/memcontrol.c: memcg_create_kmem_cache() tweaks Allocate tmp_name on demand rather than permanently consuming PATH_MAX bytes of memory. Remove the mutex which protected the static tmp_name. Cc: Glauber Costa Cc: Johannes Weiner Cc: Michal Hocko Cc: Vladimir Davydov Signed-off-by: Andrew Morton --- mm/memcontrol.c | 23 ++++++++--------------- 1 file changed, 8 insertions(+), 15 deletions(-) diff -puN mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks mm/memcontrol.c --- a/mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks +++ a/mm/memcontrol.c @@ -3400,24 +3400,18 @@ void mem_cgroup_destroy_cache(struct kme static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg, struct kmem_cache *s) { - struct kmem_cache *new = NULL; - static char *tmp_name = NULL; - static DEFINE_MUTEX(mutex); /* protects tmp_name */ + struct kmem_cache *new; + char *tmp_name; BUG_ON(!memcg_can_account_kmem(memcg)); - mutex_lock(&mutex); /* - * kmem_cache_create_memcg duplicates the given name and - * cgroup_name for this name requires RCU context. - * This static temporary buffer is used to prevent from - * pointless shortliving allocation. + * kmem_cache_create_memcg duplicates the given name and cgroup_name() + * for this name requires rcu_read_lock(). */ - if (!tmp_name) { - tmp_name = kmalloc(PATH_MAX, GFP_KERNEL); - if (!tmp_name) - goto out; - } + tmp_name = kmalloc(PATH_MAX, GFP_KERNEL); + if (!tmp_name) + return NULL; rcu_read_lock(); snprintf(tmp_name, PATH_MAX, "%s(%d:%s)", s->name, @@ -3430,8 +3424,7 @@ static struct kmem_cache *memcg_create_k new->allocflags |= __GFP_KMEMCG; else new = s; -out: - mutex_unlock(&mutex); + kfree(tmp_name); return new; } _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org