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Commit 1f979b11 authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'ipv6_percpu_rt_deadlock' 

Martin KaFai Lau says:

====================
ipv6: Fix a potential deadlock when creating pcpu rt

v1 -> v2:
A minor change in the commit message of patch 2.

This patch series fixes a potential deadlock when creating a pcpu rt.
It happens when dst_alloc() decided to run gc. Something like this:

read_lock(&table->tb6_lock);
ip6_rt_pcpu_alloc()
=> dst_alloc()
=> ip6_dst_gc()
=> write_lock(&table->tb6_lock); /* oops */

Patch 1 and 2 are some prep works.
Patch 3 is the fix.

Original report: https://bugzilla.kernel.org/show_bug.cgi?id=102291


====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 776829de 9c7370a1

net/ipv6/ip6_fib.c

+2 −0
Original line number Diff line number Diff line
@@ -172,6 +172,8 @@ static void rt6_free_pcpu(struct rt6_info *non_pcpu_rt) 
			*ppcpu_rt = NULL;

		}

	}



	non_pcpu_rt->rt6i_pcpu = NULL;

}



static void rt6_release(struct rt6_info *rt)

net/ipv6/route.c

+55 −24
Original line number Diff line number Diff line
@@ -318,8 +318,7 @@ static const struct rt6_info ip6_blk_hole_entry_template = { 
/* allocate dst with ip6_dst_ops */

static struct rt6_info *__ip6_dst_alloc(struct net *net,

					struct net_device *dev,

					int flags,

					struct fib6_table *table)

					int flags)

{

	struct rt6_info *rt = dst_alloc(&net->ipv6.ip6_dst_ops, dev,

					0, DST_OBSOLETE_FORCE_CHK, flags);
@@ -336,10 +335,9 @@ static struct rt6_info *__ip6_dst_alloc(struct net *net, 


static struct rt6_info *ip6_dst_alloc(struct net *net,

				      struct net_device *dev,

				      int flags,

				      struct fib6_table *table)

				      int flags)

{

	struct rt6_info *rt = __ip6_dst_alloc(net, dev, flags, table);

	struct rt6_info *rt = __ip6_dst_alloc(net, dev, flags);



	if (rt) {

		rt->rt6i_pcpu = alloc_percpu_gfp(struct rt6_info *, GFP_ATOMIC);
@@ -950,8 +948,7 @@ static struct rt6_info *ip6_rt_cache_alloc(struct rt6_info *ort, 
	if (ort->rt6i_flags & (RTF_CACHE | RTF_PCPU))

		ort = (struct rt6_info *)ort->dst.from;



	rt = __ip6_dst_alloc(dev_net(ort->dst.dev), ort->dst.dev,

			     0, ort->rt6i_table);

	rt = __ip6_dst_alloc(dev_net(ort->dst.dev), ort->dst.dev, 0);



	if (!rt)

		return NULL;
@@ -983,8 +980,7 @@ static struct rt6_info *ip6_rt_pcpu_alloc(struct rt6_info *rt) 
	struct rt6_info *pcpu_rt;



	pcpu_rt = __ip6_dst_alloc(dev_net(rt->dst.dev),

				  rt->dst.dev, rt->dst.flags,

				  rt->rt6i_table);

				  rt->dst.dev, rt->dst.flags);



	if (!pcpu_rt)

		return NULL;
@@ -997,32 +993,53 @@ static struct rt6_info *ip6_rt_pcpu_alloc(struct rt6_info *rt) 
/* It should be called with read_lock_bh(&tb6_lock) acquired */

static struct rt6_info *rt6_get_pcpu_route(struct rt6_info *rt)

{

	struct rt6_info *pcpu_rt, *prev, **p;

	struct rt6_info *pcpu_rt, **p;



	p = this_cpu_ptr(rt->rt6i_pcpu);

	pcpu_rt = *p;



	if (pcpu_rt)

		goto done;

	if (pcpu_rt) {

		dst_hold(&pcpu_rt->dst);

		rt6_dst_from_metrics_check(pcpu_rt);

	}

	return pcpu_rt;

}



static struct rt6_info *rt6_make_pcpu_route(struct rt6_info *rt)

{

	struct fib6_table *table = rt->rt6i_table;

	struct rt6_info *pcpu_rt, *prev, **p;



	pcpu_rt = ip6_rt_pcpu_alloc(rt);

	if (!pcpu_rt) {

		struct net *net = dev_net(rt->dst.dev);



		pcpu_rt = net->ipv6.ip6_null_entry;

		goto done;

		dst_hold(&net->ipv6.ip6_null_entry->dst);

		return net->ipv6.ip6_null_entry;

	}



	read_lock_bh(&table->tb6_lock);

	if (rt->rt6i_pcpu) {

		p = this_cpu_ptr(rt->rt6i_pcpu);

		prev = cmpxchg(p, NULL, pcpu_rt);

		if (prev) {

			/* If someone did it before us, return prev instead */

			dst_destroy(&pcpu_rt->dst);

			pcpu_rt = prev;

		}



done:

	} else {

		/* rt has been removed from the fib6 tree

		 * before we have a chance to acquire the read_lock.

		 * In this case, don't brother to create a pcpu rt

		 * since rt is going away anyway.  The next

		 * dst_check() will trigger a re-lookup.

		 */

		dst_destroy(&pcpu_rt->dst);

		pcpu_rt = rt;

	}

	dst_hold(&pcpu_rt->dst);

	rt6_dst_from_metrics_check(pcpu_rt);

	read_unlock_bh(&table->tb6_lock);

	return pcpu_rt;

}
@@ -1097,9 +1114,22 @@ static struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table, 
		rt->dst.lastuse = jiffies;

		rt->dst.__use++;

		pcpu_rt = rt6_get_pcpu_route(rt);



		if (pcpu_rt) {

			read_unlock_bh(&table->tb6_lock);

		} else {

			/* We have to do the read_unlock first

			 * because rt6_make_pcpu_route() may trigger

			 * ip6_dst_gc() which will take the write_lock.

			 */

			dst_hold(&rt->dst);

			read_unlock_bh(&table->tb6_lock);

			pcpu_rt = rt6_make_pcpu_route(rt);

			dst_release(&rt->dst);

		}



		return pcpu_rt;



	}

}
@@ -1555,7 +1585,7 @@ struct dst_entry *icmp6_dst_alloc(struct net_device *dev, 
	if (unlikely(!idev))

		return ERR_PTR(-ENODEV);



	rt = ip6_dst_alloc(net, dev, 0, NULL);

	rt = ip6_dst_alloc(net, dev, 0);

	if (unlikely(!rt)) {

		in6_dev_put(idev);

		dst = ERR_PTR(-ENOMEM);
@@ -1742,7 +1772,8 @@ int ip6_route_add(struct fib6_config *cfg) 
	if (!table)

		goto out;



	rt = ip6_dst_alloc(net, NULL, (cfg->fc_flags & RTF_ADDRCONF) ? 0 : DST_NOCOUNT, table);

	rt = ip6_dst_alloc(net, NULL,

			   (cfg->fc_flags & RTF_ADDRCONF) ? 0 : DST_NOCOUNT);



	if (!rt) {

		err = -ENOMEM;
@@ -2399,7 +2430,7 @@ struct rt6_info *addrconf_dst_alloc(struct inet6_dev *idev, 
{

	struct net *net = dev_net(idev->dev);

	struct rt6_info *rt = ip6_dst_alloc(net, net->loopback_dev,

					    DST_NOCOUNT, NULL);

					    DST_NOCOUNT);

	if (!rt)

		return ERR_PTR(-ENOMEM);