[lkml]   [2003]   [Jan]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: BUG: [2.4.18+] IDE Race Condition

Easy, it happens all the time, there are just no tests in place to see it.

We are keeping a histogram of how long every IDE DMA transfer takes
place. In ide_intr we record the time and set the start time in
ide_drive_t to 0. In ide_dma_proc, ide_dma_begin right AFTER activating
the dma, we store the current value of jiffies in start time in ide_drive_t.

In both those places we check to make sure that the value of start_time
is sensible. In ide_dma_begin, we make sure it's 0 and in ide_dma_intr,
we make sure its non-zero. Because of this race condition, we often saw
DMAs finish before they began.

In the normal kernel, the only thing I can see that could go wrong would
be that the printk

printk("%s: ide_intr: huh? expected NULL handler on exit\n", drive->name);

in ide_intr could be triggered. I've never seen it happen, but I
believe with enough effort, it could be made to occur.


Andre Hedrick wrote:

>Okay, how do you reproduce it to see the effects?
>On Mon, 27 Jan 2003, Ross Biro wrote:
>>The net effect of this race condition and the other one I spotted is
>>that you may see some interesting messages in your log file and you can
>>detect the race condition if you look for it hard enough. I don't
>>currently see any bad effects.
>> Ross
>>Ross Biro wrote:
>>>There is at least one more IDE race condition in 2.4.18 and
>>>2.4.21-pre3. Basically the interrupt for the controller being serviced
>>>is left on while setting up the next command. I'm not sure how much
>>>trouble it can cause but it does lead to some interesting stack traces.
>>>The condition
>>>if (masked_irq && hwif->irq != masked_irq)
>>>in ide_do_request should be replaced with
>>>if (!masked_irq || hwif->irq != masked_irq)
>>>in two places.
>>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>the body of a message to
>>More majordomo info at
>>Please read the FAQ at
>Andre Hedrick
>LAD Storage Consulting Group

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:32    [W:0.041 / U:2.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site