Re: [Xen-devel] [PATCH 2/2] smp: convert cpu_hotplug_begin into a blocking lock acquisition

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Feb 19, 2020 at 01:59:51PM +0100, Jan Beulich wrote:
> On 13.02.2020 12:32, Roger Pau Monne wrote:
> > Don't allow cpu_hotplug_begin to fail by converting the trylock into a
> > blocking lock acquisition. Write users of the cpu_add_remove_lock are
> > limited to CPU plug/unplug operations, and cannot deadlock between
> > themselves or other users taking the lock in read mode as
> > cpu_add_remove_lock is always locked with interrupts enabled. There
> > are also no other locks taken during the plug/unplug operations.
> 
> I don't think the goal was deadlock avoidance, but rather limiting
> of the time spent spinning while trying to acquire the lock, in
> favor of having the caller retry.

Now that the contention between read-only users is reduced as those
can take the lock in parallel I think it's safe to switch writers to
blocking mode.

Thanks, Roger.

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