Re: [PATCH/RFC] Futex mmap_sem deadlock

[Joe Korty <joe.korty@ccur.com>]

On Tue, Feb 22, 2005 at 01:30:27PM -0800, Linus Torvalds wrote:
> 
> We really have this already, and it's called "current->preempt". It 
> handles any lock at all, and doesn't add yet another special case to all 
> the architectures.
> 
> Just do
> 
> 	repeat:
> 		down_read(&current->mm->mmap_sem);
> 		get_futex_key(...) etc.
> 		queue_me(...) etc.
> 		inc_preempt_count();
> 		ret = get_user(...);
> 		dec_preempt_count();

Perhaps this should be preempt_disable .... preempt_enable.

Otherwise, a preempt attempt in get_user would not be seen
until some future preempt_enable was executed.

Regards,
Joe
--
"Money can buy bandwidth, but latency is forever" -- John Mashey