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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.12-rc6-V0.7.48-00

* William Weston <weston@sysex.net> wrote:

> Fortunately, there were some dumps (all ns83820 tx related) left in
> the logs before the machine locked:

i'm not sure it's related to the lockup - but there is a generic bug in
the driver, which in ns83820_tx_timeout() does:

local_irq_save(flags);
...
CALL do_tx_done()

spin_lock_irq(&dev->tx_lock);
...
spin_unlock_irq(&dev->tx_lock); // [1]
...
local_irq_restore(flags); // [2]
this leads to interrupts being enabled at [1], while the intention was
to enable them at [2]. To solve this bug we can do the tx-locking in
ns83820_tx_timeout(). (local_irq_disable() use in ns83820_tx_timeout()
was probably SMP-unsafe too, but needs a rare race.)

find the patch below - it's also included in the -50-05 -RT tree i just
uploaded. Can you confirm that you dont get the warnings in the -50-05
(and later) -RT kernels?

Ingo

Index: drivers/net/ns83820.c
===================================================================
--- drivers/net/ns83820.c.orig
+++ drivers/net/ns83820.c
@@ -1013,8 +1013,6 @@ static void do_tx_done(struct net_device
struct ns83820 *dev = PRIV(ndev);
u32 cmdsts, tx_done_idx, *desc;

- spin_lock_irq(&dev->tx_lock);
-
dprintk("do_tx_done(%p)\n", ndev);
tx_done_idx = dev->tx_done_idx;
desc = dev->tx_descs + (tx_done_idx * DESC_SIZE);
@@ -1070,7 +1068,6 @@ static void do_tx_done(struct net_device
netif_start_queue(ndev);
netif_wake_queue(ndev);
}
- spin_unlock_irq(&dev->tx_lock);
}

static void ns83820_cleanup_tx(struct ns83820 *dev)
@@ -1371,7 +1368,9 @@ static void ns83820_do_isr(struct net_de
* work has accumulated
*/
if ((ISR_TXDESC | ISR_TXIDLE | ISR_TXOK | ISR_TXERR) & isr) {
+ spin_lock_irq(&dev->tx_lock);
do_tx_done(ndev);
+ spin_unlock_irq(&dev->tx_lock);

/* Disable TxOk if there are no outstanding tx packets.
*/
@@ -1456,7 +1455,7 @@ static void ns83820_tx_timeout(struct ne
u32 tx_done_idx, *desc;
unsigned long flags;

- local_irq_save(flags);
+ spin_lock_irqsave(&dev->tx_lock, flags);

tx_done_idx = dev->tx_done_idx;
desc = dev->tx_descs + (tx_done_idx * DESC_SIZE);
@@ -1483,7 +1482,7 @@ static void ns83820_tx_timeout(struct ne
ndev->name,
tx_done_idx, dev->tx_free_idx, le32_to_cpu(desc[DESC_CMDSTS]));

- local_irq_restore(flags);
+ spin_unlock_irqrestore(&dev->tx_lock, flags);
}

-
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