On sg_miter_next sg_miter_stop

[va stg2010]

Mulyadi,
I referred to this comment.   "IRQ must stay disabled till   @miter@
is stopped. "
Yes my operations are atomic and I set miter->flag as SG_MITER_ATOMIC
when i call sg_miter_start()
But  from comment it  seems sg_miter_stop   should be called before
IRQ is enabled.

I also looked into sg_miter_next()   and sg_miter_stop()
implementations.  They  are calling  kmap_atomic()   and
kunmap_atomic() respectively.    Based on comment --  Is following an
illegal operation? and why?
1)  IRQ disabled
2) sg_miter_next , meaning kmap_atomic
3) IRQ enabled
4)  IRQ  disabled again little later
5) sg_miter_stop, meaning kunmap_atomic()

The above sequence caused following scheduler messages (if
sg_miter_stop()  is moved between step1 & step3 then following error
messages disappeared) :--------
BUG: scheduling while atomic: swapper/0/0xffffffff
Modules linked in: my_scsi_lld
Call Trace:
[<ffffffff8150188c>] dump_stack+0x8/0x34
[<ffffffff815024e0>] schedule+0x4c0/0x908
BUG: scheduling while atomic: swapper/0/0x00000001
Modules linked in: my_scsi_lld
Call Trace:
[<ffffffff8150188c>] dump_stack+0x8/0x34
[<ffffffff815024e0>] schedule+0x4c0/0x908
[<ffffffff81134318>] cpu_idle+0x48/0x50

BUG: scheduling while atomic: swapper/0/0x00000001
Modules linked in: my_scsi_lld
Call Trace:
[<ffffffff8150188c>] dump_stack+0x8/0x34
[<ffffffff815024e0>] schedule+0x4c0/0x908
[<ffffffff81134318>] cpu_idle+0x48/0x50

BUG: scheduling while atomic: swapper/0/0x00000001
Modules linked in: my_scsi_lld
Call Trace:
[<ffffffff8150188c>] dump_stack+0x8/0x34
[<ffffffff815024e0>] schedule+0x4c0/0x908
[<ffffffff81134318>] cpu_idle+0x48/0x50




On Tue, Mar 15, 2011 at 9:50 PM, Mulyadi Santosa
<mulyadi.santosa at gmail.com> wrote:
> Hi..
>
> On Wed, Mar 16, 2011 at 08:40, va stg2010 <va.storage2010 at gmail.com> wrote:
>> Hi
>> Can someone explain to me reason for the comment at line 332-333 of this code
>> http://lxr.linux.no/#linux+v2.6.27.7/lib/scatterlist.c#L332
>>
>> comment is:
>> "   IRQ must stay disabled till @miter@ is stopped."
>
> OK, is this the complete comment you referred?
> "Context:
>  332 *   IRQ disabled if SG_MITER_ATOMIC.  IRQ must stay disabled till
>  333 *   @miter@ is stopped.  May sleep if !SG_MITER_ATOMIC."
>
> well, then, my raw guess is, because it must be done atomically (when
> asked to do so). Usually, atomic operation has tight relationship with
> something that must be done in short time and/or must not be
> interrupted by interrupt handler.
>
> Since this is talking about scatter list, I could only guess few
> example...perhaps in bio handling?
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>