[net-next] ipv6: remove max_size check inline with ipv4

Commit Message

Jonathan Maxwell Jan. 11, 2023, 9:33 p.m. UTC

Sending Ipv6 packets in a loop via a raw socket triggers an issue where a 
route is cloned by ip6_rt_cache_alloc() for each packet sent. This quickly 
consumes the Ipv6 max_size threshold which defaults to 4096 resulting in 
these warnings:

[1]   99.187805] dst_alloc: 7728 callbacks suppressed
[2] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.
.
.
[300] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.

When this happens the packet is dropped and sendto() gets a network is 
unreachable error:

# ./a.out -s 

remaining pkt 200557 errno 101
remaining pkt 196462 errno 101
.
.
remaining pkt 126821 errno 101

Implement David Aherns suggestion to remove max_size check seeing that Ipv6 
has a GC to manage memory usage. Ipv4 already does not check max_size.

Here are some memory comparisons for Ipv4 vs Ipv6 with the patch:

Test by running 5 instances of a program that sends UDP packets to a raw 
socket 5000000 times. Compare Ipv4 and Ipv6 performance with a similar 
program.

Ipv4: 

Before test:

# grep -e Slab -e Free /proc/meminfo
MemFree:        29427108 kB
Slab:             237612 kB

# grep dst_cache /proc/slabinfo
ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
ip_dst_cache        2881   3990    192   42    2 : tunables    0    0    0 

During test:

# grep -e Slab -e Free /proc/meminfo
MemFree:        29417608 kB
Slab:             247712 kB

# grep dst_cache /proc/slabinfo
ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
ip_dst_cache       44394  44394    192   42    2 : tunables    0    0    0 

After test:

# grep -e Slab -e Free /proc/meminfo
MemFree:        29422308 kB
Slab:             238104 kB

# grep dst_cache /proc/slabinfo
ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0 

Ipv6 with patch:

Errno 101 errors are not observed anymore with the patch.

Before test:

# grep -e Slab -e Free /proc/meminfo
MemFree:        29422308 kB
Slab:             238104 kB

# grep dst_cache /proc/slabinfo
ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0 

During Test:

# grep -e Slab -e Free /proc/meminfo
MemFree:        29431516 kB
Slab:             240940 kB

# grep dst_cache /proc/slabinfo
ip6_dst_cache      11980  12064    256   32    2 : tunables    0    0    0
xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0
ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0

After Test:

# grep -e Slab -e Free /proc/meminfo
MemFree:        29441816 kB
Slab:             238132 kB

# grep dst_cache /proc/slabinfo
ip6_dst_cache       1902   2432    256   32    2 : tunables    0    0    0
xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0
ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0

Tested-by: Andrea Mayer <[e-mail]>
Signed-off-by: Jon Maxwell <[e-mail]>
---
 include/net/dst_ops.h |  2 +-
 net/core/dst.c        |  8 ++------
 net/ipv6/route.c      | 13 +++++--------
 3 files changed, 8 insertions(+), 15 deletions(-)

Comments

kernel test robot Jan. 12, 2023, 1:06 a.m. UTC | #1

Hi Jon,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Jon-Maxwell/ipv6-remove-max_size-check-inline-with-ipv4/20230112-053517
patch link:    https://lore.kernel.org/r/20230111213306.265239-1-jmaxwell37%40gmail.com
patch subject: [net-next] ipv6: remove max_size check inline with ipv4
config: m68k-allmodconfig
compiler: m68k-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/6fb29b5595df9235f531daa3af1ab4aebf0c1834
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Jon-Maxwell/ipv6-remove-max_size-check-inline-with-ipv4/20230112-053517
        git checkout 6fb29b5595df9235f531daa3af1ab4aebf0c1834
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash net/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <[e-mail]>

All errors (new ones prefixed by >>):

   net/ipv6/route.c: In function 'ip6_dst_gc':
>> net/ipv6/route.c:3298:23: error: 'gc_thresh' undeclared (first use in this function)
    3298 |         if (entries > gc_thresh)
         |                       ^~~~~~~~~
   net/ipv6/route.c:3298:23: note: each undeclared identifier is reported only once for each function it appears in


vim +/gc_thresh +3298 net/ipv6/route.c

  3286	
  3287	static void ip6_dst_gc(struct dst_ops *ops)
  3288	{
  3289		struct net *net = container_of(ops, struct net, ipv6.ip6_dst_ops);
  3290		int rt_min_interval = net->ipv6.sysctl.ip6_rt_gc_min_interval;
  3291		int rt_elasticity = net->ipv6.sysctl.ip6_rt_gc_elasticity;
  3292		int rt_gc_timeout = net->ipv6.sysctl.ip6_rt_gc_timeout;
  3293		unsigned long rt_last_gc = net->ipv6.ip6_rt_last_gc;
  3294		unsigned int val;
  3295		int entries;
  3296	
  3297		entries = dst_entries_get_fast(ops);
> 3298		if (entries > gc_thresh)
  3299			entries = dst_entries_get_slow(ops);
  3300	
  3301		if (time_after(rt_last_gc + rt_min_interval, jiffies))
  3302			goto out;
  3303	
  3304		fib6_run_gc(atomic_inc_return(&net->ipv6.ip6_rt_gc_expire), net, true);
  3305		entries = dst_entries_get_slow(ops);
  3306		if (entries < ops->gc_thresh)
  3307			atomic_set(&net->ipv6.ip6_rt_gc_expire, rt_gc_timeout >> 1);
  3308	out:
  3309		val = atomic_read(&net->ipv6.ip6_rt_gc_expire);
  3310		atomic_set(&net->ipv6.ip6_rt_gc_expire, val - (val >> rt_elasticity));
  3311	}
  3312

Patch

diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
index 88ff7bb2bb9b..632086b2f644 100644
--- a/include/net/dst_ops.h
+++ b/include/net/dst_ops.h
@@ -16,7 +16,7 @@  struct dst_ops {
 	unsigned short		family;
 	unsigned int		gc_thresh;
 
-	int			(*gc)(struct dst_ops *ops);
+	void			(*gc)(struct dst_ops *ops);
 	struct dst_entry *	(*check)(struct dst_entry *, __u32 cookie);
 	unsigned int		(*default_advmss)(const struct dst_entry *);
 	unsigned int		(*mtu)(const struct dst_entry *);
diff --git a/net/core/dst.c b/net/core/dst.c
index 6d2dd03dafa8..31c08a3386d3 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -82,12 +82,8 @@  void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
 
 	if (ops->gc &&
 	    !(flags & DST_NOCOUNT) &&
-	    dst_entries_get_fast(ops) > ops->gc_thresh) {
-		if (ops->gc(ops)) {
-			pr_notice_ratelimited("Route cache is full: consider increasing sysctl net.ipv6.route.max_size.\n");
-			return NULL;
-		}
-	}
+	    dst_entries_get_fast(ops) > ops->gc_thresh)
+		ops->gc(ops);
 
 	dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
 	if (!dst)
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index e74e0361fd92..53b09de61a4a 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -91,7 +91,7 @@  static struct dst_entry *ip6_negative_advice(struct dst_entry *);
 static void		ip6_dst_destroy(struct dst_entry *);
 static void		ip6_dst_ifdown(struct dst_entry *,
 				       struct net_device *dev, int how);
-static int		 ip6_dst_gc(struct dst_ops *ops);
+static void		 ip6_dst_gc(struct dst_ops *ops);
 
 static int		ip6_pkt_discard(struct sk_buff *skb);
 static int		ip6_pkt_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb);
@@ -3284,11 +3284,10 @@  struct dst_entry *icmp6_dst_alloc(struct net_device *dev,
 	return dst;
 }
 
-static int ip6_dst_gc(struct dst_ops *ops)
+static void ip6_dst_gc(struct dst_ops *ops)
 {
 	struct net *net = container_of(ops, struct net, ipv6.ip6_dst_ops);
 	int rt_min_interval = net->ipv6.sysctl.ip6_rt_gc_min_interval;
-	int rt_max_size = net->ipv6.sysctl.ip6_rt_max_size;
 	int rt_elasticity = net->ipv6.sysctl.ip6_rt_gc_elasticity;
 	int rt_gc_timeout = net->ipv6.sysctl.ip6_rt_gc_timeout;
 	unsigned long rt_last_gc = net->ipv6.ip6_rt_last_gc;
@@ -3296,11 +3295,10 @@  static int ip6_dst_gc(struct dst_ops *ops)
 	int entries;
 
 	entries = dst_entries_get_fast(ops);
-	if (entries > rt_max_size)
+	if (entries > gc_thresh)
 		entries = dst_entries_get_slow(ops);
 
-	if (time_after(rt_last_gc + rt_min_interval, jiffies) &&
-	    entries <= rt_max_size)
+	if (time_after(rt_last_gc + rt_min_interval, jiffies))
 		goto out;
 
 	fib6_run_gc(atomic_inc_return(&net->ipv6.ip6_rt_gc_expire), net, true);
@@ -3310,7 +3308,6 @@  static int ip6_dst_gc(struct dst_ops *ops)
 out:
 	val = atomic_read(&net->ipv6.ip6_rt_gc_expire);
 	atomic_set(&net->ipv6.ip6_rt_gc_expire, val - (val >> rt_elasticity));
-	return entries > rt_max_size;
 }
 
 static int ip6_nh_lookup_table(struct net *net, struct fib6_config *cfg,
@@ -6512,7 +6509,7 @@  static int __net_init ip6_route_net_init(struct net *net)
 #endif
 
 	net->ipv6.sysctl.flush_delay = 0;
-	net->ipv6.sysctl.ip6_rt_max_size = 4096;
+	net->ipv6.sysctl.ip6_rt_max_size = INT_MAX;
 	net->ipv6.sysctl.ip6_rt_gc_min_interval = HZ / 2;
 	net->ipv6.sysctl.ip6_rt_gc_timeout = 60*HZ;
 	net->ipv6.sysctl.ip6_rt_gc_interval = 30*HZ;