[PATCH 4/4] [RFC] ipv6: Fix for possible ipv6 seqlock deadlock
From: John Stultz
Date: Thu Sep 26 2013 - 14:35:35 EST
While enabling lockdep on seqlocks, I ran accross the warning below
caused by the ipv6 stats being updated in both irq and non-irq context.
This is a novice attempt to correct the issue, and with this patch
the warning goes away. Any better solutions would be appreciated!
[ 11.120383] =================================
[ 11.121024] [ INFO: inconsistent lock state ]
[ 11.121663] 3.12.0-rc1+ #68 Not tainted
[ 11.122229] ---------------------------------
[ 11.122867] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[ 11.123741] init/4483 [HC0[0]:SC1[3]:HE1:SE0] takes:
[ 11.124505] (&stats->syncp.seq#6){+.?...}, at: [<c1ab80c2>] ndisc_send_ns+0xe2/0x130
[ 11.125736] {SOFTIRQ-ON-W} state was registered at:
[ 11.126447] [<c10e0eb7>] __lock_acquire+0x5c7/0x1af0
[ 11.127222] [<c10e2996>] lock_acquire+0x96/0xd0
[ 11.127925] [<c1a9a2c3>] write_seqcount_begin+0x33/0x40
[ 11.128766] [<c1a9aa03>] ip6_dst_lookup_tail+0x3a3/0x460
[ 11.129582] [<c1a9e0ce>] ip6_dst_lookup_flow+0x2e/0x80
[ 11.130014] [<c1ad18e0>] ip6_datagram_connect+0x150/0x4e0
[ 11.130014] [<c1a4d0b5>] inet_dgram_connect+0x25/0x70
[ 11.130014] [<c198dd61>] SYSC_connect+0xa1/0xc0
[ 11.130014] [<c198f571>] SyS_connect+0x11/0x20
[ 11.130014] [<c198fe6b>] SyS_socketcall+0x12b/0x300
[ 11.130014] [<c1bbf880>] syscall_call+0x7/0xb
[ 11.130014] irq event stamp: 1184
[ 11.130014] hardirqs last enabled at (1184): [<c1086901>] local_bh_enable+0x71/0x110
[ 11.130014] hardirqs last disabled at (1183): [<c10868cd>] local_bh_enable+0x3d/0x110
[ 11.130014] softirqs last enabled at (0): [<c108014d>] copy_process.part.42+0x45d/0x11a0
[ 11.130014] softirqs last disabled at (1147): [<c1086e05>] irq_exit+0xa5/0xb0
[ 11.130014]
[ 11.130014] other info that might help us debug this:
[ 11.130014] Possible unsafe locking scenario:
[ 11.130014]
[ 11.130014] CPU0
[ 11.130014] ----
[ 11.130014] lock(&stats->syncp.seq#6);
[ 11.130014] <Interrupt>
[ 11.130014] lock(&stats->syncp.seq#6);
[ 11.130014]
[ 11.130014] *** DEADLOCK ***
[ 11.130014]
[ 11.130014] 3 locks held by init/4483:
[ 11.130014] #0: (rcu_read_lock){.+.+..}, at: [<c109363c>] SyS_setpriority+0x4c/0x620
[ 11.130014] #1: (((&ifa->dad_timer))){+.-...}, at: [<c108c1c0>] call_timer_fn+0x0/0xf0
[ 11.130014] #2: (rcu_read_lock){.+.+..}, at: [<c1ab6494>] ndisc_send_skb+0x54/0x5d0
[ 11.130014]
[ 11.130014] stack backtrace:
[ 11.130014] CPU: 0 PID: 4483 Comm: init Not tainted 3.12.0-rc1+ #68
[ 11.130014] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 11.130014] 00000000 00000000 c55e5c10 c1bb0e71 c57128b0 c55e5c4c c1badf79 c1ec1123
[ 11.130014] c1ec1484 00001183 00000000 00000000 00000001 00000003 00000001 00000000
[ 11.130014] c1ec1484 00000004 c5712dcc 00000000 c55e5c84 c10de492 00000004 c10755f2
[ 11.130014] Call Trace:
[ 11.130014] [<c1bb0e71>] dump_stack+0x4b/0x66
[ 11.130014] [<c1badf79>] print_usage_bug+0x1d3/0x1dd
[ 11.130014] [<c10de492>] mark_lock+0x282/0x2f0
[ 11.130014] [<c10755f2>] ? kvm_clock_read+0x22/0x30
[ 11.130014] [<c10dd8b0>] ? check_usage_backwards+0x150/0x150
[ 11.130014] [<c10e0e74>] __lock_acquire+0x584/0x1af0
[ 11.130014] [<c10b1baf>] ? sched_clock_cpu+0xef/0x190
[ 11.130014] [<c10de58c>] ? mark_held_locks+0x8c/0xf0
[ 11.130014] [<c10e2996>] lock_acquire+0x96/0xd0
[ 11.130014] [<c1ab80c2>] ? ndisc_send_ns+0xe2/0x130
[ 11.130014] [<c1ab66d3>] ndisc_send_skb+0x293/0x5d0
[ 11.130014] [<c1ab80c2>] ? ndisc_send_ns+0xe2/0x130
[ 11.130014] [<c1ab80c2>] ndisc_send_ns+0xe2/0x130
[ 11.130014] [<c108cc32>] ? mod_timer+0xf2/0x160
[ 11.130014] [<c1aa706e>] ? addrconf_dad_timer+0xce/0x150
[ 11.130014] [<c1aa70aa>] addrconf_dad_timer+0x10a/0x150
[ 11.130014] [<c1aa6fa0>] ? addrconf_dad_completed+0x1c0/0x1c0
[ 11.130014] [<c108c233>] call_timer_fn+0x73/0xf0
[ 11.130014] [<c108c1c0>] ? __internal_add_timer+0xb0/0xb0
[ 11.130014] [<c1aa6fa0>] ? addrconf_dad_completed+0x1c0/0x1c0
[ 11.130014] [<c108c5b1>] run_timer_softirq+0x141/0x1e0
[ 11.130014] [<c1086b20>] ? __do_softirq+0x70/0x1b0
[ 11.130014] [<c1086b70>] __do_softirq+0xc0/0x1b0
[ 11.130014] [<c1086e05>] irq_exit+0xa5/0xb0
[ 11.130014] [<c106cfd5>] smp_apic_timer_interrupt+0x35/0x50
[ 11.130014] [<c1bbfbca>] apic_timer_interrupt+0x32/0x38
[ 11.130014] [<c10936ed>] ? SyS_setpriority+0xfd/0x620
[ 11.130014] [<c10e26c9>] ? lock_release+0x9/0x240
[ 11.130014] [<c10936d7>] ? SyS_setpriority+0xe7/0x620
[ 11.130014] [<c1bbee6d>] ? _raw_read_unlock+0x1d/0x30
[ 11.130014] [<c1093701>] SyS_setpriority+0x111/0x620
[ 11.130014] [<c109363c>] ? SyS_setpriority+0x4c/0x620
[ 11.130014] [<c1bbf880>] syscall_call+0x7/0xb
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
Cc: Patrick McHardy <kaber@xxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
net/ipv6/ip6_output.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 3a692d5..7614b63 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -908,8 +908,13 @@ static int ip6_dst_lookup_tail(struct sock *sk,
return 0;
out_err_release:
- if (err == -ENETUNREACH)
+ if (err == -ENETUNREACH) {
+ unsigned long flags;
+ /* some of the stats are locked in irq context */
+ local_irq_save(flags);
IP6_INC_STATS_BH(net, NULL, IPSTATS_MIB_OUTNOROUTES);
+ local_irq_restore(flags);
+ }
dst_release(*dst);
*dst = NULL;
return err;
--
1.8.1.2
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