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Subject[patch] forcedeth: fix locking bug with netconsole
Subject: forcedeth: fix locking bug with netconsole
From: Ingo Molnar <mingo@elte.hu>

while using netconsole on forcedeth, lockdep noticed the following
locking bug:

=================================
[ INFO: inconsistent lock state ]
2.6.24-rc6 #6
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---------------------------------
inconsistent {softirq-on-W} -> {in-softirq-W} usage.
udevd/719 [HC0[0]:SC1[1]:HE1:SE0] takes:
(_xmit_ETHER){-+..}, at: [<c043062e>] dev_watchdog+0x1c/0xb9
{softirq-on-W} state was registered at:
[<c0147f67>] mark_held_locks+0x4e/0x66
[<c014810e>] trace_hardirqs_on+0xfe/0x136
[<c048ae63>] _spin_unlock_irq+0x22/0x42
[<c02ec617>] nv_start_xmit_optimized+0x347/0x37a
[<c042c80d>] netpoll_send_skb+0xa4/0x147
[<c042d4a6>] netpoll_send_udp+0x238/0x242
[<c02f44f6>] write_msg+0x6d/0x9b
[<c012c129>] __call_console_drivers+0x4e/0x5a
[<c012c18c>] _call_console_drivers+0x57/0x5b
[<c012c2dd>] release_console_sem+0x11c/0x1b9
[<c012caeb>] register_console+0x1eb/0x1f3
[<c06ae673>] init_netconsole+0x119/0x15f
[<c069149b>] kernel_init+0x147/0x294
[<c01058cb>] kernel_thread_helper+0x7/0x10
[<ffffffff>] 0xffffffff
irq event stamp: 950
hardirqs last enabled at (950): [<c048ae63>] _spin_unlock_irq+0x22/0x42
hardirqs last disabled at (949): [<c048aaf7>] _spin_lock_irq+0xc/0x38
softirqs last enabled at (0): [<c012a29c>] copy_process+0x375/0x126d
softirqs last disabled at (947): [<c0106d43>] do_softirq+0x61/0xc6

other info that might help us debug this:
no locks held by udevd/719.

stack backtrace:
Pid: 719, comm: udevd Not tainted 2.6.24-rc6 #6
[<c0105c46>] show_trace_log_lvl+0x12/0x25
[<c01063ec>] show_trace+0xd/0x10
[<c010670c>] dump_stack+0x57/0x5f
[<c0147505>] print_usage_bug+0x10a/0x117
[<c0147c38>] mark_lock+0x121/0x402
[<c01488b6>] __lock_acquire+0x3d1/0xb64
[<c0149405>] lock_acquire+0x4e/0x6a
[<c048a99b>] _spin_lock+0x23/0x32
[<c043062e>] dev_watchdog+0x1c/0xb9
[<c0133e4a>] run_timer_softirq+0x133/0x193
[<c0130907>] __do_softirq+0x78/0xed
[<c0106d43>] do_softirq+0x61/0xc6
=======================
eth1: link down

the fix is to disable/restore irqs instead of disable/enable.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
drivers/net/forcedeth.c | 18 ++++++++++--------
net/core/netpoll.c | 3 +++
2 files changed, 13 insertions(+), 8 deletions(-)

Index: linux/drivers/net/forcedeth.c
===================================================================
--- linux.orig/drivers/net/forcedeth.c
+++ linux/drivers/net/forcedeth.c
@@ -1854,6 +1854,7 @@ static int nv_start_xmit(struct sk_buff
struct ring_desc* start_tx;
struct ring_desc* prev_tx;
struct nv_skb_map* prev_tx_ctx;
+ unsigned long flags;

/* add fragments to entries count */
for (i = 0; i < fragments; i++) {
@@ -1863,10 +1864,10 @@ static int nv_start_xmit(struct sk_buff

empty_slots = nv_get_empty_tx_slots(np);
if (unlikely(empty_slots <= entries)) {
- spin_lock_irq(&np->lock);
+ spin_lock_irqsave(&np->lock, flags);
netif_stop_queue(dev);
np->tx_stop = 1;
- spin_unlock_irq(&np->lock);
+ spin_unlock_irqrestore(&np->lock, flags);
return NETDEV_TX_BUSY;
}

@@ -1929,13 +1930,13 @@ static int nv_start_xmit(struct sk_buff
tx_flags_extra = skb->ip_summed == CHECKSUM_PARTIAL ?
NV_TX2_CHECKSUM_L3 | NV_TX2_CHECKSUM_L4 : 0;

- spin_lock_irq(&np->lock);
+ spin_lock_irqsave(&np->lock, flags);

/* set tx flags */
start_tx->flaglen |= cpu_to_le32(tx_flags | tx_flags_extra);
np->put_tx.orig = put_tx;

- spin_unlock_irq(&np->lock);
+ spin_unlock_irqrestore(&np->lock, flags);

dprintk(KERN_DEBUG "%s: nv_start_xmit: entries %d queued for transmission. tx_flags_extra: %x\n",
dev->name, entries, tx_flags_extra);
@@ -1971,6 +1972,7 @@ static int nv_start_xmit_optimized(struc
struct ring_desc_ex* prev_tx;
struct nv_skb_map* prev_tx_ctx;
struct nv_skb_map* start_tx_ctx;
+ unsigned long flags;

/* add fragments to entries count */
for (i = 0; i < fragments; i++) {
@@ -1980,10 +1982,10 @@ static int nv_start_xmit_optimized(struc

empty_slots = nv_get_empty_tx_slots(np);
if (unlikely(empty_slots <= entries)) {
- spin_lock_irq(&np->lock);
+ spin_lock_irqsave(&np->lock, flags);
netif_stop_queue(dev);
np->tx_stop = 1;
- spin_unlock_irq(&np->lock);
+ spin_unlock_irqrestore(&np->lock, flags);
return NETDEV_TX_BUSY;
}

@@ -2059,7 +2061,7 @@ static int nv_start_xmit_optimized(struc
start_tx->txvlan = 0;
}

- spin_lock_irq(&np->lock);
+ spin_lock_irqsave(&np->lock, flags);

if (np->tx_limit) {
/* Limit the number of outstanding tx. Setup all fragments, but
@@ -2085,7 +2087,7 @@ static int nv_start_xmit_optimized(struc
start_tx->flaglen |= cpu_to_le32(tx_flags | tx_flags_extra);
np->put_tx.ex = put_tx;

- spin_unlock_irq(&np->lock);
+ spin_unlock_irqrestore(&np->lock, flags);

dprintk(KERN_DEBUG "%s: nv_start_xmit_optimized: entries %d queued for transmission. tx_flags_extra: %x\n",
dev->name, entries, tx_flags_extra);
Index: linux/net/core/netpoll.c
===================================================================
--- linux.orig/net/core/netpoll.c
+++ linux/net/core/netpoll.c
@@ -284,6 +284,7 @@ static void netpoll_send_skb(struct netp
/* try until next clock tick */
for (tries = jiffies_to_usecs(1)/USEC_PER_POLL;
tries > 0; --tries) {
+ WARN_ON_ONCE(!irqs_disabled());
if (netif_tx_trylock(dev)) {
if (!netif_queue_stopped(dev) &&
!netif_subqueue_stopped(dev, skb))
@@ -297,8 +298,10 @@ static void netpoll_send_skb(struct netp

/* tickle device maybe there is some cleanup */
netpoll_poll(np);
+ WARN_ON_ONCE(!irqs_disabled());

udelay(USEC_PER_POLL);
+ WARN_ON_ONCE(!irqs_disabled());
}
local_irq_restore(flags);
}

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