Messages in this thread |  | | Date | Wed, 22 Oct 2014 09:57:52 -0700 | From | Laura Abbott <> | Subject | Deadlock with CMA and CPU hotplug |
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Hi,
We've run into a AB/BA deadlock situation involving a driver lock and the CPU hotplug lock on a 3.10 based kernel. The situation is this:
CPU 0 CPU 1 ----- ---- Start CPU hotplug mutex_lock(&cpu_hotplug.lock) Run CPU hotplug notifier data for driver comes in mutex_lock(&driver_lock) driver calls dma_alloc_coherent alloc_contig_range lru_add_drain_all get_online_cpus() mutex_lock(&cpu_hotplug.lock)
Driver hotplug notifier runs mutex_lock(&driver_lock)
The driver itself is out of tree right now[1] and we're looking at ways to rework the driver. The best option for rework right now though might result in some performance penalties. The size that's being allocated can't easily be converted to an atomic allocation either It seems like this might be a limitation of where CMA/ dma_alloc_coherent could potentially be used and make drivers unnecessarily aware of CPU hotplug locking.
Does this seem like an actual problem that needs to be fixed or is trying to use CMA in a CPU hotplug notifier path just asking for trouble?
Thanks, Laura
[1] For reference, the driver is a version of https://lkml.org/lkml/2014/10/7/495 although that particular posted version allocates memory at probe instead of runtime and probably doesn't have the deadlock.
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