Re: [Xen-devel] [PATCH v6 3/4] xen/rcu: add assertions to debug build

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.03.2020 14:06, Juergen Gross wrote:
> Xen's RCU implementation relies on no softirq handling taking place
> while being in a RCU critical section. Add ASSERT()s in debug builds
> in order to catch any violations.
> 
> For that purpose modify rcu_read_[un]lock() to use a dedicated percpu
> counter additional to preempt_[en|dis]able() as this enables to test
> that condition in __do_softirq() (ASSERT_NOT_IN_ATOMIC() is not
> usable there due to __cpu_up() calling process_pending_softirqs()
> while holding the cpu hotplug lock).
> 
> While at it switch the rcu_read_[un]lock() implementation to static
> inline functions instead of macros.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with one remark:

> @@ -91,16 +114,23 @@ typedef struct _rcu_read_lock rcu_read_lock_t;
>   * will be deferred until the outermost RCU read-side critical section
>   * completes.
>   *
> - * It is illegal to block while in an RCU read-side critical section.
> + * It is illegal to process softirqs while in an RCU read-side critical 
> section.

The latest with the re-added preempt_disable(), wouldn't this better
say "... to process softirqs or block ..."?

Jan

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