Re: [PATCH] IB core: Fix locking on device numbers allocation

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

 > When the driver needs to dynamically allocate char device numbers in systems
 > with more than IB_UVERBS_MAX_DEVICES, it releases map lock, allocates a new
 > range and a new device number from that range, and only then re-acquires the
 > lock. This must be protected for the same reasoning that the map_lock spinlock
 > is used. Without protecting we could also end up calling alloc_chrdev_region()
 > a nubmer of times and cause a leakage. Fix this by replacing map_lock with a
 > mutex and apply on the all the allocation code.

Looks like a good catch.  I assume you found this through inspection and
not hitting it practice?  Also it seems user_mad.c would need the same fix.

Although looking at this I wonder if we do need that lock... we don't
seem to do any locking when we do the clear_bit in the dev_map, and all
of this is done through the device add/remove callback, which seems to
be serialized by the device_mutex in device.c.  But we probably don't
want to make that a requirement in case we parallelize in the future.

 - R.
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Roland Dreier  <rolandd-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>
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