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Re: [Xen-devel] [PATCHv6] x86/xen: allow privcmd hypercalls to be preempted

On 19/02/15 16:50, Boris Ostrovsky wrote:
> On 02/19/2015 10:23 AM, David Vrabel wrote:
>> Hypercalls submitted by user space tools via the privcmd driver can
>> take a long time (potentially many 10s of seconds) if the hypercall
>> has many sub-operations.
>> A fully preemptible kernel may deschedule such as task in any upcall
>> called from a hypercall continuation.
>> However, in a kernel with voluntary or no preemption, hypercall
>> continuations in Xen allow event handlers to be run but the task
>> issuing the hypercall will not be descheduled until the hypercall is
>> complete and the ioctl returns to user space.  These long running
>> tasks may also trigger the kernel's soft lockup detection.
>> Add xen_preemptible_hcall_begin() and xen_preemptible_hcall_end() to
>> bracket hypercalls that may be preempted.  Use these in the privcmd
>> driver.
>> When returning from an upcall, call xen_maybe_preempt_hcall() which
>> adds a schedule point if if the current task was within a preemptible
>> hypercall.
>> Since _cond_resched() can move the task to a different CPU, clear and
>> set xen_in_preemptible_hcall around the call.
>> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

Thanks.  Applied to stable/for-linus-3.20.


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