Re: BUG or not? GFP_KERNEL with interrupts disabled.

On Thu, 27 Mar 2003, Linus Torvalds wrote:

On Thu, 27 Mar 2003, David S. Miller wrote:

quoted

Ok, so can we add a:

	if (irqs_disabled())
		BUG();

check to do_softirq()?

I'd suggest making it a counting warning (with a static counter per
local-bh-enable macro expansion) and adding it to local_bh_enable() -
otherwise it will only BUG()  when the (potentially rare) condition
happens - instead of always giving a nice backtrace of exact problem 
spots.

So, to return to my original question...  local_bh_count() > 0 when 
a BH is running or after local_bh_disable().  local_irq_count() > 0 in 
interrupt context, but not necessarily when interrupts are disabled.

This makes checks like the following (in alloc_skb) asymmetric:

    if (in_interrupt() && (gfp_mask & __GFP_WAIT)) {
        static int count = 0;
        if (++count < 5) {
            printk(KERN_ERR "alloc_skb called nonatomically "
                   "from interrupt %p\n", NET_CALLER(size));
            BUG();

In a driver I'm writing, this bug was hidden until I switched from using
write_lock_irqsave() to write_lock_bh().  Shouldn't this bug also be
announced if interrupts are disabled?  (I understand that disabling bh/irq
in the correct order will ensure that this bug is properly detected, but
it seems like a strange policy to rely on correct coding to catch a bug.)

-- 
Dan Eble [off-list ref]  _____  .
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