From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCHv2] x86/xen: allow privcmd hypercalls to be preempted Date: Thu, 27 Feb 2014 14:28:34 +0000 Message-ID: <530F4B92.90700@citrix.com> References: <1392310767-19347-1-git-send-email-david.vrabel@citrix.com> <20140224191810.GA7023@phenom.dumpdata.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140224191810.GA7023@phenom.dumpdata.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Konrad Rzeszutek Wilk Cc: Boris Ostrovsky , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 24/02/14 19:18, Konrad Rzeszutek Wilk wrote: > On Thu, Feb 13, 2014 at 04:59:27PM +0000, David Vrabel wrote: >> From: David Vrabel >> >> 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 preempt_schedule_irq() if the >> current task was within a preemptible hypercall. >> >> Since preempt_schedule_irq() can move the task to a different CPU, >> clear and set xen_in_preemptible_hcall around the call. >> >> Signed-off-by: David Vrabel >> --- >> Changes in v2: >> - Use per-cpu variable to mark preemptible regions >> - Call preempt_schedule_irq() from the correct place in >> xen_hypervisor_callback > > > 12929 ERROR: "xen_in_preemptible_hcall" [drivers/xen/xen-privcmd.ko] undefined! You have privcmd built as a module so xen_in_preemptible_hcall needs to be exported. I'll send a v3 shortly. David