Re: spinlocks() are severely broken in 2.2.X and 2.4.X for modules

[David S. Miller]

   Date: 	Sat, 1 Jul 2000 10:09:56 +0200 (CEST)
   From: =?ISO-8859-1?Q?G=E9rard_Roudier?= <[e-mail]>

   On Fri, 30 Jun 2000, Jeff V. Merkey wrote:

   [...]

   > void NWLockLRU(LRU_HANDLE *lru_handle)
   > {
   >    spinlock_irqsave(&lru_handle->LRU_spinlock, lru_handle->LRU_flags);

   Does not seem to me safe to store irq flags in shared data structures.
   SMP .vs. UP does not seem to matter here.

In fact this is also a problem in that it encourages people to believe
that doing irqsave/irqrestore for the same "flags" in different
functions is ok.  It is not and will crash on some architectures.

For example, this is OK:

{
	unsigned long flags;

	spin_lock_irqsave(&lock, flags);
	...
	spin_unlock_irqrestore(&lock, flags);
}

This is not OK:

void bar(unsigned long flags)
{
	spin_unlock_irqrestore(&lock, flags);
}

void foo(void)
{
	spin_lock_irqsave(&lock, flags);
	...
	bar();
}

It will crash on Sparc for example, it will probably cause problems
on some other non-x86 ports as well.

Later,
David S. Miller
[e-mail]