From mboxrd@z Thu Jan 1 00:00:00 1970 From: Amos Kong Subject: Re: [PATCH 2/2] virtio-rng: fix stuck in catting hwrng attributes Date: Sun, 14 Sep 2014 09:16:17 +0800 Message-ID: <20140914011617.GB1032@zen.redhat.com> References: <1410340027-15373-1-git-send-email-akong@redhat.com> <1410340027-15373-3-git-send-email-akong@redhat.com> <20140911060838.GF19202@grmbl.mre> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: herbert.xu@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org To: Amit Shah Return-path: Content-Disposition: inline In-Reply-To: <20140911060838.GF19202@grmbl.mre> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: kvm.vger.kernel.org On Thu, Sep 11, 2014 at 11:38:38AM +0530, Amit Shah wrote: > On (Wed) 10 Sep 2014 [17:07:07], Amos Kong wrote: > > When I check hwrng attributes in sysfs, cat process always gets > > stuck if guest has only 1 vcpu and uses a slow rng backend. > > > > Currently we check if there is any tasks waiting to be run on > > current cpu in rng_dev_read() by need_resched(). But need_resched() > > doesn't work because rng_dev_read() is executing in user context. > > > > This patch removed need_resched() and increase delay to 10 jiffies, > > then other tasks can have chance to execute protected code. > > Delaying 1 jiffy also works, but 10 jiffies is safer. Hi Amit, > I'd prefer two patches for this one: one to remove the need_resched() > check, and the other to increase the timeout. If Rusty agrees with this fix, I will respin to update the commitlog with clear description and split the patches to 3. Thanks for the review. > Anyway, > > Reviewed-by: Amit Shah -- Amos.