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Subject[patch 02/45] udp: Wrong locking code in udp seq_file infrastructure
-stable review patch.  If anyone has any objections, please let us know.

From: Vitaly Mayatskikh <>

[ Upstream commit 30842f2989aacfaba3ccb39829b3417be9313dbe ]

Reading zero bytes from /proc/net/udp or other similar files which use
the same seq_file udp infrastructure panics kernel in that way:

[ BUG: bad unlock balance detected! ]
read/1985 is trying to release lock (&table->hash[i].lock) at:
[<ffffffff81321d83>] udp_seq_stop+0x27/0x29
but there are no more locks to release!

other info that might help us debug this:
1 lock held by read/1985:
#0: (&p->lock){--..}, at: [<ffffffff810eefb6>] seq_read+0x38/0x348

stack backtrace:
Pid: 1985, comm: read Not tainted 2.6.29-rc8 #9
Call Trace:
[<ffffffff81321d83>] ? udp_seq_stop+0x27/0x29
[<ffffffff8106dab9>] print_unlock_inbalance_bug+0xd6/0xe1
[<ffffffff8106db62>] lock_release_non_nested+0x9e/0x1c6
[<ffffffff810ef030>] ? seq_read+0xb2/0x348
[<ffffffff8106bdba>] ? mark_held_locks+0x68/0x86
[<ffffffff81321d83>] ? udp_seq_stop+0x27/0x29
[<ffffffff8106dde7>] lock_release+0x15d/0x189
[<ffffffff8137163c>] _spin_unlock_bh+0x1e/0x34
[<ffffffff81321d83>] udp_seq_stop+0x27/0x29
[<ffffffff810ef239>] seq_read+0x2bb/0x348
[<ffffffff810eef7e>] ? seq_read+0x0/0x348
[<ffffffff8111aedd>] proc_reg_read+0x90/0xaf
[<ffffffff810d878f>] vfs_read+0xa6/0x103
[<ffffffff8106bfac>] ? trace_hardirqs_on_caller+0x12f/0x153
[<ffffffff810d88a2>] sys_read+0x45/0x69
[<ffffffff8101123a>] system_call_fastpath+0x16/0x1b
BUG: scheduling while atomic: read/1985/0xffffff00
INFO: lockdep is turned off.
Modules linked in: cpufreq_ondemand acpi_cpufreq freq_table dm_multipath kvm ppdev snd_hda_codec_analog snd_hda_intel snd_hda_codec snd_hwdep snd_seq_dummy snd_seq_oss snd_seq_midi_event arc4 snd_s
eq ecb thinkpad_acpi snd_seq_device iwl3945 hwmon sdhci_pci snd_pcm_oss sdhci rfkill mmc_core snd_mixer_oss i2c_i801 mac80211 yenta_socket ricoh_mmc i2c_core iTCO_wdt snd_pcm iTCO_vendor_support rs
rc_nonstatic snd_timer snd lib80211 cfg80211 soundcore snd_page_alloc video parport_pc output parport e1000e [last unloaded: scsi_wait_scan]
Pid: 1985, comm: read Not tainted 2.6.29-rc8 #9
Call Trace:
[<ffffffff8106b456>] ? __debug_show_held_locks+0x1b/0x24
[<ffffffff81043660>] __schedule_bug+0x7e/0x83
[<ffffffff8136ede9>] schedule+0xce/0x838
[<ffffffff810d7972>] ? fsnotify_access+0x5f/0x67
[<ffffffff810112d0>] ? sysret_careful+0xb/0x37
[<ffffffff8106be9c>] ? trace_hardirqs_on_caller+0x1f/0x153
[<ffffffff8137127b>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[<ffffffff810112f6>] sysret_careful+0x31/0x37
read[1985]: segfault at 7fffc479bfe8 ip 0000003e7420a180 sp 00007fffc479bfa0 error 6
Kernel panic - not syncing: Aiee, killing interrupt handler!

udp_seq_stop() tries to unlock not yet locked spinlock. The lock was lost
during splitting global udp_hash_lock to subsequent spinlocks.

Signed-off by: Vitaly Mayatskikh <>
Acked-by: Eric Dumazet <>
Signed-off-by: David S. Miller <>
Signed-off-by: Chris Wright <>
net/ipv4/udp.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1614,7 +1614,8 @@ static struct sock *udp_get_next(struct
} while (sk && (!net_eq(sock_net(sk), net) || sk->sk_family != state->family));

if (!sk) {
- spin_unlock_bh(&state->udp_table->hash[state->bucket].lock);
+ if (state->bucket < UDP_HTABLE_SIZE)
+ spin_unlock_bh(&state->udp_table->hash[state->bucket].lock);
return udp_get_first(seq, state->bucket + 1);
return sk;
@@ -1632,6 +1633,9 @@ static struct sock *udp_get_idx(struct s

static void *udp_seq_start(struct seq_file *seq, loff_t *pos)
+ struct udp_iter_state *state = seq->private;
+ state->bucket = UDP_HTABLE_SIZE;
return *pos ? udp_get_idx(seq, *pos-1) : SEQ_START_TOKEN;

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