From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net V3 2/2] ptr_ring: fail on large queue size (>64K) Date: Thu, 8 Feb 2018 17:50:54 +0200 Message-ID: <20180208173024-mutt-send-email-mst@kernel.org> References: <1518062365-8596-1-git-send-email-jasowang@redhat.com> <1518062365-8596-2-git-send-email-jasowang@redhat.com> <20180208064602-mutt-send-email-mst@kernel.org> <118d4e49-ac55-c4d3-13ed-8828b9d110a2@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org To: Jason Wang Return-path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39038 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750929AbeBHPuz (ORCPT ); Thu, 8 Feb 2018 10:50:55 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8AC5A76F94 for ; Thu, 8 Feb 2018 15:50:54 +0000 (UTC) Content-Disposition: inline In-Reply-To: <118d4e49-ac55-c4d3-13ed-8828b9d110a2@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Feb 08, 2018 at 03:11:22PM +0800, Jason Wang wrote: > > > On 2018年02月08日 12:52, Michael S. Tsirkin wrote: > > On Thu, Feb 08, 2018 at 11:59:25AM +0800, Jason Wang wrote: > > > We need limit the maximum size of queue, otherwise it may cause > > > several side effects e.g slab will warn when the size exceeds > > > KMALLOC_MAX_SIZE. Using KMALLOC_MAX_SIZE still looks too so this patch > > > tries to limit it to 64K. This value could be revisited if we found a > > > real case that needs more. > > > > > > Reported-by: syzbot+e4d4f9ddd4295539735d@syzkaller.appspotmail.com > > > Fixes: 2e0ab8ca83c12 ("ptr_ring: array based FIFO for pointers") > > > Signed-off-by: Jason Wang > > > --- > > > include/linux/ptr_ring.h | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h > > > index 2af71a7..5858d48 100644 > > > --- a/include/linux/ptr_ring.h > > > +++ b/include/linux/ptr_ring.h > > > @@ -44,6 +44,8 @@ struct ptr_ring { > > > void **queue; > > > }; > > Seems like a weird location for a define. Either put defines on > > top of the file, or near where they are used. I prefer the > > second option. > > Ok. > > > > > > +#define PTR_RING_MAX_ALLOC 65536 > > > + > > I guess it's an arbitrary number. Seems like a sufficiently large one, > > but pls add a comment so readers don't wonder. And please explain what > > it does: > > > > /* Callers can create ptr_ring structures with userspace-supplied > > * parameters. This sets a limit on the size to make that usecase > > * safe. If you ever change this, make sure to audit all callers. > > */ > > > > Also I think we should generally use either hex 0x10000 or (1 << 16). > > I agree the number is arbitrary, so I still prefer the KMALLOC_MAX_SIZE > especially consider it was used by pfifo_fast now. Try to limit it to an > arbitrary may break lots of exist setups. E.g just google "txqueuelen > 100000" can give me a lots of search results. > > We can do any kind of optimization on top but not for -net now. > > Thanks Interesting. I have an idea for fixing this, but maybe for now KMALLOC_MAX_SIZE does make sense. It's unfortunate that this value is architecture dependent. The patch still needs code comments though, and fix the math to use the proper size. > > > > > /* Note: callers invoking this in a loop must use a compiler barrier, > > > * for example cpu_relax(). > > > * > > > @@ -466,6 +468,8 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r, > > > static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp) > > > { > > > + if (size > PTR_RING_MAX_ALLOC) > > > + return NULL; > > > return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO); > > > } > > > -- > > > 2.7.4