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Re: [PATCH 2/2] xen: privcmd: Add support for ioeventfd
- To: Viresh Kumar <viresh.kumar@xxxxxxxxxx>, Alex Bennée <alex.bennee@xxxxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Mon, 9 Oct 2023 12:58:24 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, Vincent Guittot <vincent.guittot@xxxxxxxxxx>, stratos-dev@xxxxxxxxxxxxxxxxxxx, Erik Schilling <erik.schilling@xxxxxxxxxx>, Manos Pitsidianakis <manos.pitsidianakis@xxxxxxxxxx>, Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 09 Oct 2023 10:58:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09.10.23 12:53, Viresh Kumar wrote:
On 09-10-23, 10:40, Alex Bennée wrote:
I thought generally sync points act as full barriers. Doing a bunch of
grepping I think ends at:
static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
{
unsigned long curr = (unsigned long)current;
return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
}
so you should already have completed your writes by that point.
I am not sure if depending on such indirect mechanisms to implement
barriers for you is a good idea.
The situation here probably requires explicit barriers to make sure it
doesn't break in future ?
Depending on lock implementations to include the needed barriers is fine IMO.
That is one central objective locks must ensure: to make sure any updates in
a locked region are operating on consistent data and being observable by
others after leaving the locked region.
Juergen
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