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    SubjectRe: [PATCH RFC tip/core/rcu 23/23] vhost: add __rcu annotations
    On Thu, May 13, 2010 at 07:50:50AM +0300, Michael S. Tsirkin wrote:
    > On Wed, May 12, 2010 at 04:00:57PM -0700, Paul E. McKenney wrote:
    > > On Thu, May 13, 2010 at 12:48:47AM +0300, Michael S. Tsirkin wrote:
    > > > On Wed, May 12, 2010 at 02:33:42PM -0700, Paul E. McKenney wrote:
    > > > > From: Arnd Bergmann <arnd@relay.de.ibm.com>
    > > > >
    > > > > Also add rcu_dreference_protected() for code paths where locks are held.
    > > > >
    > > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > > > > Cc: "Michael S. Tsirkin" <mst@redhat.com>
    > > >
    > > > Maybe long lines can be fixed? Otherwise looks ok.
    > >
    > > Done. I introduced locals to make it fit.
    >
    > Just pls check this does not lead to unused variable
    > warnings when the whole lockdep is off.

    Will do! It should not, because the assignment happens independently
    of lockdep, but I will nevertheless build both ways.

    I am also merging in Peter Zijlstra's suggestion of leveraging the
    existing lockdep on workqueues.

    Thanx, Paul

    > > One other thing... We need some API that says "we are running in the
    > > context of a work queue." Otherwise, we will get false positives when
    > > called in a work queue without locks held.
    > >
    > > Any thoughts? One approach would be to create a separate lockdep class
    > > for vhost workqueue state, similar to the approach used in instrument
    > > rcu_read_lock() and friends.
    > >
    > > Thanx, Paul
    > >
    > > > > ---
    > > > > drivers/vhost/net.c | 11 ++++++++---
    > > > > drivers/vhost/vhost.c | 14 ++++++++------
    > > > > drivers/vhost/vhost.h | 4 ++--
    > > > > 3 files changed, 18 insertions(+), 11 deletions(-)
    > > > >
    > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
    > > > > index 9777583..945c5cb 100644
    > > > > --- a/drivers/vhost/net.c
    > > > > +++ b/drivers/vhost/net.c
    > > > > @@ -364,7 +364,10 @@ static void vhost_net_disable_vq(struct vhost_net *n,
    > > > > static void vhost_net_enable_vq(struct vhost_net *n,
    > > > > struct vhost_virtqueue *vq)
    > > > > {
    > > > > - struct socket *sock = vq->private_data;
    > > > > + struct socket *sock;
    > > > > +
    > > > > + sock = rcu_dereference_protected(vq->private_data,
    > > > > + lockdep_is_held(&vq->mutex));
    > > > > if (!sock)
    > > > > return;
    > > > > if (vq == n->vqs + VHOST_NET_VQ_TX) {
    > > > > @@ -380,7 +383,8 @@ static struct socket *vhost_net_stop_vq(struct vhost_net *n,
    > > > > struct socket *sock;
    > > > >
    > > > > mutex_lock(&vq->mutex);
    > > > > - sock = vq->private_data;
    > > > > + sock = rcu_dereference_protected(vq->private_data,
    > > > > + lockdep_is_held(&vq->mutex));
    > > > > vhost_net_disable_vq(n, vq);
    > > > > rcu_assign_pointer(vq->private_data, NULL);
    > > > > mutex_unlock(&vq->mutex);
    > > > > @@ -518,7 +522,8 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
    > > > > }
    > > > >
    > > > > /* start polling new socket */
    > > > > - oldsock = vq->private_data;
    > > > > + oldsock = rcu_dereference_protected(vq->private_data,
    > > > > + lockdep_is_held(&vq->mutex));
    > > > > if (sock == oldsock)
    > > > > goto done;
    > > > >
    > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
    > > > > index e69d238..fc0c077 100644
    > > > > --- a/drivers/vhost/vhost.c
    > > > > +++ b/drivers/vhost/vhost.c
    > > > > @@ -180,7 +180,7 @@ long vhost_dev_reset_owner(struct vhost_dev *dev)
    > > > > vhost_dev_cleanup(dev);
    > > > >
    > > > > memory->nregions = 0;
    > > > > - dev->memory = memory;
    > > > > + RCU_INIT_POINTER(dev->memory, memory);
    > > > > return 0;
    > > > > }
    > > > >
    > > > > @@ -212,8 +212,9 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
    > > > > fput(dev->log_file);
    > > > > dev->log_file = NULL;
    > > > > /* No one will access memory at this point */
    > > > > - kfree(dev->memory);
    > > > > - dev->memory = NULL;
    > > > > + kfree(rcu_dereference_protected(dev->memory,
    > > > > + lockdep_is_held(&dev->mutex)));
    > > > > + RCU_INIT_POINTER(dev->memory, NULL);
    > > > > if (dev->mm)
    > > > > mmput(dev->mm);
    > > > > dev->mm = NULL;
    > > > > @@ -294,14 +295,14 @@ static int vq_access_ok(unsigned int num,
    > > > > /* Caller should have device mutex but not vq mutex */
    > > > > int vhost_log_access_ok(struct vhost_dev *dev)
    > > > > {
    > > > > - return memory_access_ok(dev, dev->memory, 1);
    > > > > + return memory_access_ok(dev, rcu_dereference_protected(dev->memory, lockdep_is_held(&dev->mutex)), 1);
    > > > > }
    > > > >
    > > > > /* Verify access for write logging. */
    > > > > /* Caller should have vq mutex and device mutex */
    > > > > static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base)
    > > > > {
    > > > > - return vq_memory_access_ok(log_base, vq->dev->memory,
    > > > > + return vq_memory_access_ok(log_base, rcu_dereference_protected(vq->dev->memory, lockdep_is_held(&dev->mutex)),
    > > > > vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
    > > > > (!vq->log_used || log_access_ok(log_base, vq->log_addr,
    > > > > sizeof *vq->used +
    > > > > @@ -342,7 +343,8 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
    > > > >
    > > > > if (!memory_access_ok(d, newmem, vhost_has_feature(d, VHOST_F_LOG_ALL)))
    > > > > return -EFAULT;
    > > > > - oldmem = d->memory;
    > > > > + oldmem = rcu_dereference_protected(d->memory,
    > > > > + lockdep_is_held(&d->mutex));
    > > > > rcu_assign_pointer(d->memory, newmem);
    > > > > synchronize_rcu();
    > > > > kfree(oldmem);
    > > > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
    > > > > index 44591ba..240396c 100644
    > > > > --- a/drivers/vhost/vhost.h
    > > > > +++ b/drivers/vhost/vhost.h
    > > > > @@ -92,7 +92,7 @@ struct vhost_virtqueue {
    > > > > * work item execution acts instead of rcu_read_lock() and the end of
    > > > > * work item execution acts instead of rcu_read_lock().
    > > > > * Writers use virtqueue mutex. */
    > > > > - void *private_data;
    > > > > + void __rcu *private_data;
    > > > > /* Log write descriptors */
    > > > > void __user *log_base;
    > > > > struct vhost_log log[VHOST_NET_MAX_SG];
    > > > > @@ -102,7 +102,7 @@ struct vhost_dev {
    > > > > /* Readers use RCU to access memory table pointer
    > > > > * log base pointer and features.
    > > > > * Writers use mutex below.*/
    > > > > - struct vhost_memory *memory;
    > > > > + struct vhost_memory __rcu *memory;
    > > > > struct mm_struct *mm;
    > > > > struct mutex mutex;
    > > > > unsigned acked_features;
    > > > > --
    > > > > 1.7.0.6


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