Re: page fault in cli / sti safe or not

[Andrea Arcangeli <andrea@suse.de>]

On Thu, 30 Mar 2000, Andi Kleen wrote:

>On Thu, Mar 30, 2000 at 06:49:27AM +0200, pnilesh@in.ibm.com wrote:
>>      I tried to page fault in cli () / sti() , but there was no deadlock. I
>> had perception that a deadlock would occur. However what might have I now
>> believe is that age fault always ocuur in any processes context , they will
>> panic in interrupt handler. So when a page fault occurs the page fault
>> handler is called and if the page is not found in the memory then a disk
>> read is scheduled the faulting process is put to sleep and  schedule() is
>> called to run new process. The schedule () implicitly calls sti() and hence
>> there is no deadlock.
>
>You are right. It does not make much sense though, because the locking
>guarantee you wanted from cli() is broken. Also there is a bug in most
>linux kernels that they do turn on the interrupts only after the 
>scheduler task queue has run. Some programs do a lot of work in
>the scheduler tq (isdn4linux, reiserfs, in some cases the serial driver),
>which can cause bad interrupt latencies (often leading the SMP TLB IPI
>timed out messages on faster SMP boxes) 

for the record I uploaded the latest patch for the SMP TLB IPI here (it
fixes the thing Andi is talking about):

	ftp://ftp.*.kernel.org/pub/linux/kernel/people/andrea/patches/v2.2/2.2.15pre16/tq_scheduler-cli-1.gz

Andrea

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux.eu.org/Linux-MM/