From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas@monjalon.net>
Subject: Re: [PATCH 18.11] malloc: fix deadlock when using malloc
	stats
Date: Fri, 21 Dec 2018 13:09:23 +0100
Message-ID: <8322983.QTS3aZyW4V@xps>
References: <884a355bde19652d57c253c6b36036571c4f46ee.1543926108.git.anatoly.burakov@intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7Bit
Cc: dev@dpdk.org, stable@dpdk.org, ferruh.yigit@intel.com,
 bruce.richardson@intel.com, arybchenko@solarflare.com, olivier.matz@6wind.com
To: Anatoly Burakov <anatoly.burakov@intel.com>
Return-path: <dev-bounces@dpdk.org>
In-Reply-To: <884a355bde19652d57c253c6b36036571c4f46ee.1543926108.git.anatoly.burakov@intel.com>
List-Id: DPDK patches and discussions <dev.dpdk.org>
List-Unsubscribe: <https://mails.dpdk.org/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://mails.dpdk.org/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <https://mails.dpdk.org/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

04/12/2018 13:22, Anatoly Burakov:
> Currently, malloc statistics and external heap creation code
> use memory hotplug lock as a way to synchronize accesses to
> heaps (as in, locking the hotplug lock to prevent list of heaps
> from changing under our feet). At the same time, malloc
> statistics code will also lock the heap because it needs to
> access heap data and does not want any other thread to allocate
> anything from that heap.
> 
> In such scheme, it is possible to enter a deadlock with the
> following sequence of events:
> 
> thread 1		thread 2
> rte_malloc()
> 			rte_malloc_dump_stats()
> take heap lock
> 			take hotplug lock
> failed to allocate,
> attempt to take
> hotplug lock
> 			attempt to take heap lock
> 
> Neither thread will be able to continue, as both of them are
> waiting for the other one to drop the lock. Adding an
> additional lock will require an ABI change, so instead of
> that, make malloc statistics calls thread-unsafe with
> respect to creating/destroying heaps.
> 
> Fixes: 72cf92b31855 ("malloc: index heaps using heap ID rather than NUMA node")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---
> 
> Notes:
>     IMO this is the best we can do for 18.11 without breaking ABI.
>     For 19.02, we can introduce a new global heap lock (something
>     i should've done in the first place...), so this patch is
>     not applicable to 19.02. For 19.02, we can fix this properly
>     by introducing another lock and breaking the EAL ABI.
>     
>     Not sure where to put docs update, feedback welcome.

This patch is also changing the API, because functions become not thread-safe.
I think you should note it in the release notes.
About 19.02, do we want to take this patch (with release notes updated)?