Hi,
On Sunday 24 June 2007, Thanos Kyritsis wrote:
> On Saturday 23 June 2007, Bartlomiej Zolnierkiewicz wrote:
> > Hi,
>
> Hello, thanks for answering :-D
>
>
> > Also could you try running UP kernel without PREEMPT and see
> > if it makes difference?
>
> Yes, it did make a difference. I've just tried both UP and SMP kernels
> (22-rc5) *without* PREEMPT. Neither of these locked!
Thanks for testing.
IIRC SMP kernel without PREEMPT should also fail (or not?),
it could be that we are hitting some generic PREEMPT bug.
Cc:ed linux-kernel@ in hope that some PREEMPT guru lends us a hand.
[ original thread is here:
http://www.mail-archive.com/[email protected]/msg07380.html ]
> I also tried UP with PREEMPT and it locks.
>
> > Adding a couple of printk-s to ide.c::set_using_dma() and
> > ide.c::ide_spin_wait_hwgroup() will for sure help in debugging
> > it further.
>
> I just tried that as well. I placed printk-s when entering and exiting
> these 2 functions and when they use spin_lock_irq() and
> spin_unlock_irq(), and then watched the output:
>
> I didn't see something odd. For every hdparm execution, set_using_dma()
> is called, it successfully calls ide_spin_wait_hwgroup(), then
> set_using_dma() finishes.
> After set_using_dma() finishes, one more ide_spin_wait_hwgroup()
> is called and finishes.
>
> This pattern happens always, no matter if the kernel will eventually
> lock (preempt) or not lock (no preempt), with absolutely no
> differences.
>
> entering ide.c::set_using_dma()
> |
> entering ide.c::ide_spin_wait_hwgroup()
> ide.c::ide_spin_wait_hwgroup: LOCK
> exiting ide.c::ide_spin_wait_hwgroup()
> |
> ide.c::set_using_dma: set ->busy flag, unlock and let it ride
> ide.c::set_using_dma: UNLOCK
> ide.c::set_using_dma: lock, clear ->busy flag and unlock before leaving
> ide.c::set_using_dma: LOCK
> ide.c::set_using_dma: UNLOCK
> |
> exiting ide.c::set_using_dma()
>
> entering ide.c::ide_spin_wait_hwgroup()
> ide.c::ide_spin_wait_hwgroup: LOCK
> exiting ide.c::ide_spin_wait_hwgroup()
>
> The above gets printed twice (one for the hda hdparm and one for hdb).
>
> But I noticed something extra.
>
> Sometimes, the ide_spin_wait_hwgroup() that runs either before the 1st
> set_using_dma() or between the 1st and the 2nd (1st for hda, 2nd for
> hdb) (*but never the one called last*) is waiting A LOT inside the busy
> loop (while (hwgroup->busy)).
>
> I think PREEMPT kernels always produce a lot of this while loop output,
> and then print the above pattern, then lock.
>
> Non-PREEMPT kernels don't always produce the huge while loop output,
> only sometimes, but they never have locking problem.
> I don't know if this is at all relevant to the problem. Perhaps it's
> normal that during some of the bootups the IDE device group is busy
> while during other bootups it's not busy, right ?
Yes, this is expected behavior (especially when you mix SMP in)
unless of course ide_spin_wait_hwgroupt() fails (timeouts).
> However, since all functions exit properly, should I try to place
> printk-s in other functions as well ?
ide_do_request() and hwgroup->busy flag but as this could produce *a*lot*
of output (serial or net console would be required to capture the log for
the lockup case).
> (I kind of need and appreciate guideance in order to help you, because
> I've never been in the kernel hacking business before :) )
No problem, happy hacking. :)
Thanks,
Bart
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