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Message-ID: <1439452683-964514-4-git-send-email-kafai@fb.com>
Date: Thu, 13 Aug 2015 00:58:03 -0700
From: Martin KaFai Lau <kafai@...com>
To: netdev <netdev@...r.kernel.org>,
"Steinar H. Gunderson" <sgunderson@...foot.com>
CC: Hannes Frederic Sowa <hannes@...essinduktion.org>,
FB Kernel Team <kernel-team@...com>
Subject: [PATCH RFC net 3/3] ipv6: Fix potential deadlock when creating pcpu rt
rt6_make_pcpu_route() is called under read_lock(&table->tb6_lock).
rt6_make_pcpu_route() calls ip6_rt_pcpu_alloc(rt) which then
calls dst_alloc(). dst_alloc() _may_ call ip6_dst_gc() which takes
the write_lock(&tabl->tb6_lock). A visualized version:
read_lock(&table->tb6_lock);
rt6_make_pcpu_route();
=> ip6_rt_pcpu_alloc();
=> dst_alloc();
=> ip6_dst_gc();
=> write_lock(&table->tb6_lock); /* oops */
The fix is to do a read_unlock first before calling ip6_rt_pcpu_alloc().
A reported stack:
[141625.537638] INFO: rcu_sched self-detected stall on CPU { 27} (t=60000 jiffies g=4159086 c=4159085 q=2139)
[141625.547469] Task dump for CPU 27:
[141625.550881] mtr R running task 0 22121 22081 0x00000008
[141625.558069] 0000000000000000 ffff88103f363d98 ffffffff8106e488 000000000000001b
[141625.565641] ffffffff81684900 ffff88103f363db8 ffffffff810702b0 0000000008000000
[141625.573220] ffffffff81684900 ffff88103f363de8 ffffffff8108df9f ffff88103f375a00
[141625.580803] Call Trace:
[141625.583345] <IRQ> [<ffffffff8106e488>] sched_show_task+0xc1/0xc6
[141625.589650] [<ffffffff810702b0>] dump_cpu_task+0x35/0x39
[141625.595144] [<ffffffff8108df9f>] rcu_dump_cpu_stacks+0x6a/0x8c
[141625.601320] [<ffffffff81090606>] rcu_check_callbacks+0x1f6/0x5d4
[141625.607669] [<ffffffff810940c8>] update_process_times+0x2a/0x4f
[141625.613925] [<ffffffff8109fbee>] tick_sched_handle+0x32/0x3e
[141625.619923] [<ffffffff8109fc2f>] tick_sched_timer+0x35/0x5c
[141625.625830] [<ffffffff81094a1f>] __hrtimer_run_queues+0x8f/0x18d
[141625.632171] [<ffffffff81094c9e>] hrtimer_interrupt+0xa0/0x166
[141625.638258] [<ffffffff8102bf2a>] local_apic_timer_interrupt+0x4e/0x52
[141625.645036] [<ffffffff8102c36f>] smp_apic_timer_interrupt+0x39/0x4a
[141625.651643] [<ffffffff8140b9e8>] apic_timer_interrupt+0x68/0x70
[141625.657895] <EOI> [<ffffffff81346ee8>] ? dst_destroy+0x7c/0xb5
[141625.664188] [<ffffffff813d45b5>] ? fib6_flush_trees+0x20/0x20
[141625.670272] [<ffffffff81082b45>] ? queue_write_lock_slowpath+0x60/0x6f
[141625.677140] [<ffffffff8140aa33>] _raw_write_lock_bh+0x23/0x25
[141625.683218] [<ffffffff813d4553>] __fib6_clean_all+0x40/0x82
[141625.689124] [<ffffffff813d45b5>] ? fib6_flush_trees+0x20/0x20
[141625.695207] [<ffffffff813d6058>] fib6_clean_all+0xe/0x10
[141625.700854] [<ffffffff813d60d3>] fib6_run_gc+0x79/0xc8
[141625.706329] [<ffffffff813d0510>] ip6_dst_gc+0x85/0xf9
[141625.711718] [<ffffffff81346d68>] dst_alloc+0x55/0x159
[141625.717105] [<ffffffff813d09b5>] __ip6_dst_alloc.isra.32+0x19/0x63
[141625.723620] [<ffffffff813d1830>] ip6_pol_route+0x36a/0x3e8
[141625.729441] [<ffffffff813d18d6>] ip6_pol_route_output+0x11/0x13
[141625.735700] [<ffffffff813f02c8>] fib6_rule_action+0xa7/0x1bf
[141625.741698] [<ffffffff813d18c5>] ? ip6_pol_route_input+0x17/0x17
[141625.748043] [<ffffffff81357c48>] fib_rules_lookup+0xb5/0x12a
[141625.754050] [<ffffffff81141628>] ? poll_select_copy_remaining+0xf9/0xf9
[141625.761002] [<ffffffff813f0535>] fib6_rule_lookup+0x37/0x5c
[141625.766914] [<ffffffff813d18c5>] ? ip6_pol_route_input+0x17/0x17
[141625.773260] [<ffffffff813d008c>] ip6_route_output+0x7a/0x82
[141625.779177] [<ffffffff813c44c8>] ip6_dst_lookup_tail+0x53/0x112
[141625.785437] [<ffffffff813c45c3>] ip6_dst_lookup_flow+0x2a/0x6b
[141625.791604] [<ffffffff813ddaab>] rawv6_sendmsg+0x407/0x9b6
[141625.797423] [<ffffffff813d7914>] ? do_ipv6_setsockopt.isra.8+0xd87/0xde2
[141625.804464] [<ffffffff8139d4b4>] inet_sendmsg+0x57/0x8e
[141625.810028] [<ffffffff81329ba3>] sock_sendmsg+0x2e/0x3c
[141625.815588] [<ffffffff8132be57>] SyS_sendto+0xfe/0x143
[141625.821063] [<ffffffff813dd551>] ? rawv6_setsockopt+0x5e/0x67
[141625.827146] [<ffffffff8132c9f8>] ? sock_common_setsockopt+0xf/0x11
[141625.833660] [<ffffffff8132c08c>] ? SyS_setsockopt+0x81/0xa2
[141625.839565] [<ffffffff8140ac17>] entry_SYSCALL_64_fastpath+0x12/0x6a
Fixes: d52d3997f843 ("pv6: Create percpu rt6_info")
Signed-off-by: Martin KaFai Lau <kafai@...com>
CC: Hannes Frederic Sowa <hannes@...essinduktion.org>
Reported-by: Steinar H. Gunderson <sgunderson@...foot.com>
---
net/ipv6/ip6_fib.c | 2 ++
net/ipv6/route.c | 44 +++++++++++++++++++++++++++++++++-----------
2 files changed, 35 insertions(+), 11 deletions(-)
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 55d1986..548c623 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -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)
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 0a82653..d155864 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1007,27 +1007,39 @@ static struct rt6_info *rt6_get_pcpu_route(struct rt6_info *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;
}
- p = this_cpu_ptr(rt->rt6i_pcpu);
- prev = cmpxchg(p, NULL, pcpu_rt);
- if (prev) {
- /* If someone did it before us, return prev instead */
+ 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;
+ }
+ } 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 = prev;
+ pcpu_rt = rt;
}
-
-done:
dst_hold(&pcpu_rt->dst);
rt6_dst_from_metrics_check(pcpu_rt);
+ read_unlock_bh(&table->tb6_lock);
return pcpu_rt;
}
@@ -1103,11 +1115,21 @@ redo_rt6_select:
rt->dst.__use++;
pcpu_rt = rt6_get_pcpu_route(rt);
- if (!pcpu_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);
+ }
- read_unlock_bh(&table->tb6_lock);
return pcpu_rt;
+
}
}
--
1.8.1
--
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