Messages in this thread | | | Date | Tue, 03 Nov 2009 22:11:12 +0100 | From | Eric Dumazet <> | Subject | Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server |
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Michael S. Tsirkin a écrit : > > Paul, you acked this previously. Should I add you acked-by line so > people calm down? If you would rather I replace > rcu_dereference/rcu_assign_pointer with rmb/wmb, I can do this. > Or maybe patch Documentation to explain this RCU usage? >
So you believe I am over-reacting to this dubious use of RCU ?
RCU documentation is already very complex, we dont need to add yet another subtle use, and makes it less readable.
It seems you use 'RCU api' in drivers/vhost/net.c as convenient macros :
#define rcu_dereference(p) ({ \ typeof(p) _________p1 = ACCESS_ONCE(p); \ smp_read_barrier_depends(); \ (_________p1); \ })
#define rcu_assign_pointer(p, v) \ ({ \ if (!__builtin_constant_p(v) || \ ((v) != NULL)) \ smp_wmb(); \ (p) = (v); \ })
There are plenty regular uses of smp_wmb() in kernel, not related to Read Copy Update, there is nothing wrong to use barriers with appropriate comments.
(And you already use mb(), wmb(), rmb(), smp_wmb() in your patch)
BTW there is at least one locking bug in vhost_net_set_features()
Apparently, mutex_unlock() doesnt trigger a fault if mutex is not locked by current thread... even with DEBUG_MUTEXES / DEBUG_LOCK_ALLOC
static void vhost_net_set_features(struct vhost_net *n, u64 features) { size_t hdr_size = features & (1 << VHOST_NET_F_VIRTIO_NET_HDR) ? sizeof(struct virtio_net_hdr) : 0; int i; <<!>> mutex_unlock(&n->dev.mutex); n->dev.acked_features = features; smp_wmb(); for (i = 0; i < VHOST_NET_VQ_MAX; ++i) { mutex_lock(&n->vqs[i].mutex); n->vqs[i].hdr_size = hdr_size; mutex_unlock(&n->vqs[i].mutex); } mutex_unlock(&n->dev.mutex); vhost_net_flush(n); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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