On Thursday 31 August 2006 20:00, John Zavgren wrote:
> Greetings:
>
> I'm trying to create a pause after each packet transmission in
> arch/um/drivers/net_kern.c so that I can model packet tranmsission
> times.
>
> I'm using a call to:
> schedule_timeout_interruptible(msecs_to_jiffies(125));
>
> When I boot up my UML host... it complains:
>
> BUG: scheduling while atomic: avahi-daemon/0x00000100/1981
> 0f43b81c: [<080580f4>] dump_stack+0x1c/0x20
> 0f43b834: [<081955c3>] schedule+0x49/0x467
> 0f43b87c: [<08196106>] schedule_timeout+0x7b/0x9c
> 0f43b8b4: [<08196148>] schedule_timeout_interruptible+0x21/0x23
> 0f43b8c0: [<0805df6c>] uml_net_start_xmit+0x5c/0xae
The warning is legitimate.
You cannot sleep in interrupt context or while holding a spinlock, because the
scheduler could sleep to another thread which then disables preemption and
requests that spinlock: it would never obtain it, leading to deadlock. You
could use msleep but it consumes CPU power (i.e. during msleep() the CPU is
used in a empty loop to waste time).
To avoid it you should schedule before getting or after releasing the involved
spinlocks, probably by adding that call in dev_queue_xmit() after spin_unlock
(there are different sending paths, patch all of them).
This is better explained in kernel hacking texts (like
Documentation/DocBook/kernel-{hacking,locking}.tmpl, which you can compile to
get pdf or html), or in Linux Device Drivers which can be freely downloaded.
--
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale!
http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com
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