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Date: Wed, 5 May 2010 02:59:56 +0300 From: "Michael S. Tsirkin" <mst@...hat.com> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com, eric.dumazet@...il.com, Arnd Bergmann <arnd@...ay.de.ibm.com>, Arnd Bergmann <arnd@...db.de> Subject: Re: [PATCH tip/core/rcu 43/48] vhost: add __rcu annotations On Tue, May 04, 2010 at 04:57:50PM -0700, Paul E. McKenney wrote: > On Wed, May 05, 2010 at 12:39:36AM +0300, Michael S. Tsirkin wrote: > > On Tue, May 04, 2010 at 01:19:53PM -0700, Paul E. McKenney wrote: > > > From: Arnd Bergmann <arnd@...ay.de.ibm.com> > > > > > > Signed-off-by: Arnd Bergmann <arnd@...db.de> > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > > > Cc: "Michael S. Tsirkin" <mst@...hat.com> > > > --- > > > drivers/vhost/net.c | 6 +++--- > > > drivers/vhost/vhost.c | 12 ++++++------ > > > drivers/vhost/vhost.h | 4 ++-- > > > 3 files changed, 11 insertions(+), 11 deletions(-) > > > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > > index 9777583..36e8dec 100644 > > > --- a/drivers/vhost/net.c > > > +++ b/drivers/vhost/net.c > > > @@ -364,7 +364,7 @@ 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 = rcu_dereference(vq->private_data); > > > > This should be rcu_dereference_const as well: it is called > > with vq mutex held. > > How about the following? > > struct socket *sock; > > sock = rcu_dereference_protected(vq->private_data, > lockdep_is_held(&vq->mutex)); > > This could be used for some (though not all) of these situations. > > And just so you know... The fact that this is here in the first > place is actually my mistake -- my intention was to include the __rcu > annotations and nothing else, then follow up with bug fixes. In fact, > the alert reader will have noted that there is in fact no such thing > as rcu_dereference_const(). And have concluded that none of my test > machines use vhost. :-/ > > But as long as we are here, might as well complete the annotation... > > So I have inserted guesses for the lockdep_is_held() expressions below > for your amusement. Please let me know what I should be using instead. I'll go over it. Could you point me to documentation to the API I should use with this patch? > > > if (!sock) > > > return; > > > if (vq == n->vqs + VHOST_NET_VQ_TX) { > > > @@ -380,7 +380,7 @@ 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_const(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 +518,7 @@ 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_const(vq->private_data); > > oldsock = rcu_dereference_protected(vq->private_data, > lockdep_is_held(&vq->mutex)); > > Though I can't say I see where this lock is actually acquired in this > case... Just above: mutex_lock(&vq->mutex); /* Verify that ring has been setup correctly. */ if (!vhost_vq_access_ok(vq)) { r = -EFAULT; goto err_vq; } sock = get_socket(fd); if (IS_ERR(sock)) { r = PTR_ERR(sock); goto err_vq; } /* start polling new socket */ > > > if (sock == oldsock) > > > goto done; > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index e69d238..fc9bde2 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_assign_pointer(dev->memory, memory); > > > > This is called when there can be no active readers, so the smp_wmb > > inside rcu_assign_pointer isn't really needed. > > Use RCU_INIT_POINTER or something like this instead? > > Good point! Fixed. > > > > return 0; > > > } > > > > > > @@ -212,8 +212,8 @@ 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_const(dev->memory)); > > kfree(rcu_dereference_protected(dev->memory, > lockdep_is_held(&dev->mutex)); > > > > + rcu_assign_pointer(dev->memory, NULL); > > > > Same here. > > Fixed -- any in any case, we can always use RCU_INIT_POINTER() when > assigning NULL. > > > > if (dev->mm) > > > mmput(dev->mm); > > > dev->mm = NULL; > > > @@ -294,14 +294,14 @@ 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_const(dev->memory), 1); > > return memory_access_ok(dev, rcu_dereference_protected(dev->memory, lockdep_is_held(&dev->mutex)), 1); > > And yes, we do need an rcu_dereference_vqdev() wrapper function, but just > want to identify the mutexes for the moment. > > Maybe a separate rcu_dereference_vq() as well -- but you tell me! > > > > } > > > > > > /* 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(vq->dev->memory), > > > > rcu_dereference_const. This is called under vq mutex and the comment > > above it says as much. > > return memory_access_ok(dev, rcu_dereference_protected(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 +342,7 @@ 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_const(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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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