[dpdk-dev] [PATCH 18.11] malloc: fix deadlock when using malloc stats

Thomas Monjalon thomas at monjalon.net
Fri Dec 21 13:09:23 CET 2018

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 at dpdk.org
> Signed-off-by: Anatoly Burakov <anatoly.burakov at 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)?

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