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/linux-ide@xxxxxxxxxxxxxxx/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 - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
