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Subject[PATCH] ipv6: fix possible deadlock in ip6_fl_purge / ip6_fl_gc
Date
Use spin_lock_bh in ip6_fl_purge() to prevent following potentially
deadlock scenario between ip6_fl_purge() and ip6_fl_gc() timer.

=================================
[ INFO: inconsistent lock state ]
3.19.0 #1 Not tainted
---------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
swapper/5/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
(ip6_fl_lock){+.?...}, at: [<ffffffff8171155d>] ip6_fl_gc+0x2d/0x180
{SOFTIRQ-ON-W} state was registered at:
[<ffffffff810ee9a0>] __lock_acquire+0x4a0/0x10b0
[<ffffffff810efd54>] lock_acquire+0xc4/0x2b0
[<ffffffff81751d2d>] _raw_spin_lock+0x3d/0x80
[<ffffffff81711798>] ip6_flowlabel_net_exit+0x28/0x110
[<ffffffff815f9759>] ops_exit_list.isra.1+0x39/0x60
[<ffffffff815fa320>] cleanup_net+0x100/0x1e0
[<ffffffff810ad80a>] process_one_work+0x20a/0x830
[<ffffffff810adf4b>] worker_thread+0x11b/0x460
[<ffffffff810b42f4>] kthread+0x104/0x120
[<ffffffff81752bfc>] ret_from_fork+0x7c/0xb0
irq event stamp: 84640
hardirqs last enabled at (84640): [<ffffffff81752080>] _raw_spin_unlock_irq+0x30/0x50
hardirqs last disabled at (84639): [<ffffffff81751eff>] _raw_spin_lock_irq+0x1f/0x80
softirqs last enabled at (84628): [<ffffffff81091ad1>] _local_bh_enable+0x21/0x50
softirqs last disabled at (84629): [<ffffffff81093b7d>] irq_exit+0x12d/0x150

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(ip6_fl_lock);
<Interrupt>
lock(ip6_fl_lock);

*** DEADLOCK ***

Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
net/ipv6/ip6_flowlabel.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_flowlabel.c b/net/ipv6/ip6_flowlabel.c
index 2f780cb..f45d6db 100644
--- a/net/ipv6/ip6_flowlabel.c
+++ b/net/ipv6/ip6_flowlabel.c
@@ -172,7 +172,7 @@ static void __net_exit ip6_fl_purge(struct net *net)
{
int i;

- spin_lock(&ip6_fl_lock);
+ spin_lock_bh(&ip6_fl_lock);
for (i = 0; i <= FL_HASH_MASK; i++) {
struct ip6_flowlabel *fl;
struct ip6_flowlabel __rcu **flp;
@@ -190,7 +190,7 @@ static void __net_exit ip6_fl_purge(struct net *net)
flp = &fl->next;
}
}
- spin_unlock(&ip6_fl_lock);
+ spin_unlock_bh(&ip6_fl_lock);
}

static struct ip6_flowlabel *fl_intern(struct net *net,
--
1.7.1


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