[PATCH] uml: fix spinlock recursion and sleep-inside-spinlock in error path

In this error path, when the interface has had a problem, we call dev_close(),
which is disallowed for two reasons:

*) takes again the UML internal spinlock, inside the ->stop method of this
   device
*) can be called in process context only, while we're in interrupt context.

I've also thought that calling dev_close() may be a wrong policy to follow,
but it's not up to me to decide that.

However, we may end up with multiple dev_close() queued on the same device.
But the initial test for (dev->flags & IFF_UP) makes this harmless, though -
and dev_close() is supposed to care about races with itself.  So there's no
harm in delaying the shutdown, IMHO.

Something to mark the interface as "going to shutdown" would be appreciated,
but dev_deactivate has the same problems as dev_close(), so we can't use it
either.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/um/drivers/net_kern.c b/arch/um/drivers/net_kern.c
index f3442ce29a215d2baea803d75aed6d4b40cdc951..8ebb2241ad4263ef2fd1cac2e472d66671862cd7 100644 (file)
--- a/arch/um/drivers/net_kern.c
+++ b/arch/um/drivers/net_kern.c
@@ -68,6 +68,11 @@ static int uml_net_rx(struct net_device *dev)
        return pkt_len;
 }
 
+static void uml_dev_close(void* dev)
+{
+       dev_close( (struct net_device *) dev);
+}
+
 irqreturn_t uml_net_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 {
        struct net_device *dev = dev_id;
@@ -80,15 +85,21 @@ irqreturn_t uml_net_interrupt(int irq, void *dev_id, struct pt_regs *regs)
        spin_lock(&lp->lock);
        while((err = uml_net_rx(dev)) > 0) ;
        if(err < 0) {
+               DECLARE_WORK(close_work, uml_dev_close, dev);
                printk(KERN_ERR 
                       "Device '%s' read returned %d, shutting it down\n", 
                       dev->name, err);
-               dev_close(dev);
+               /* dev_close can't be called in interrupt context, and takes
+                * again lp->lock.
+                * And dev_close() can be safely called multiple times on the
+                * same device, since it tests for (dev->flags & IFF_UP). So
+                * there's no harm in delaying the device shutdown. */
+               schedule_work(&close_work);
                goto out;
        }
        reactivate_fd(lp->fd, UM_ETH_IRQ);
 
- out:
+out:
        spin_unlock(&lp->lock);
        return(IRQ_HANDLED);
 }