On Sat, Feb 11, 2012 at 3:09 PM, tip-bot for Don Zickus <dzickus at redhat.com> wrote: > Commit-ID: ?d9bc9be89629445758670220787683e37c93f6c1 > Gitweb: ? ? http://git.kernel.org/tip/d9bc9be89629445758670220787683e37c93f6c1 > Author: ? ? Don Zickus <dzickus at redhat.com> > AuthorDate: Thu, 9 Feb 2012 16:53:41 -0500 > Committer: ?Ingo Molnar <mingo at elte.hu> > CommitDate: Sat, 11 Feb 2012 15:38:53 +0100 > > x86/kdump: No need to disable ioapic/lapic in crash path > > A customer of ours noticed when their machine crashed, kdump did > not work but hung instead. ?Using their firmware dumping > solution they grabbed a vmcore and decoded the stacks on the > cpus. ?What they noticed seemed to be a rare deadlock with the > ioapic_lock. > > ?CPU4: > ?machine_crash_shutdown > ?-> machine_ops.crash_shutdown > ? ?-> native_machine_crash_shutdown > ? ? ? -> kdump_nmi_shootdown_cpus ------> Send NMI to other CPUs > ? ? ? -> disable_IO_APIC > ? ? ? ? ?-> clear_IO_APIC > ? ? ? ? ? ? -> clear_IO_APIC_pin > ? ? ? ? ? ? ? ?-> ioapic_read_entry > ? ? ? ? ? ? ? ? ? -> spin_lock_irqsave(&ioapic_lock, flags) > ? ? ? ? ? ? ? ? ? ---Infinite loop here--- > > ?CPU0: > ?do_IRQ > ?-> handle_irq > ? ?-> handle_edge_irq > ? ? ? ?-> ack_apic_edge > ? ? ? ? ? -> move_native_irq > ? ? ? ? ? ? ? -> mask_IO_APIC_irq > ? ? ? ? ? ? ? ? ?-> mask_IO_APIC_irq_desc > ? ? ? ? ? ? ? ? ? ? -> spin_lock_irqsave(&ioapic_lock, flags) > ? ? ? ? ? ? ? ? ? ? ---Receive NMI here after getting spinlock--- > ? ? ? ? ? ? ? ? ? ? ? ?-> nmi > ? ? ? ? ? ? ? ? ? ? ? ? ? -> do_nmi > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?-> crash_nmi_callback > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?---Infinite loop here--- > > The problem is that although kdump tries to shutdown minimal > hardware, it still needs to disable the IO APIC. ?This requires > spinlocks which may be held by another cpu. ?This other cpu is > being held infinitely in an NMI context by kdump in order to > serialize the crashing path. ?Instant deadlock. > > Eric brought up a point that because the boot code was > restructured we may not need to disable the io apic any more in > the crash path. ?The original concern that led to the > development of disable_IO_APIC, was that the jiffies calibration > on boot up relied on the PIT timer for reference. ?Access to the > PIT required 8259 interrupts to be working. ?This wouldn't work > if the ioapic needed to be configured. ?So on panic path, the > ioapic was reconfigured to use virtual wire mode to allow the 8259 to passthrough. > > Those concerns don't hold true now, thanks to the jiffies > calibration code not needing the PIT. ?As a result, we can > remove this call and simplify the locking needed in the panic > path. > > The same work allowed us to remove the need to disable the local > apic on shutdown too. ?This should allow us to jump to the > second a little faster. > > I tested kdump on an Ivy Bridge platform, a Pentium4 and an old > athlon that did not have an ioapic. ?All three were successful. > > I also tested using lkdtm that would use jprobes to panic the > system when entering do_IRQ. ?The idea was to see how the system > reacted with an interrupt pending in the second kernel. ?My > core2 quad successfully kdump'd 3 times in a row with no issues. > > v2: removed the disable lapic code too with this commit, kdump is not working anymore on my setups with Nehalem, Westmere, sandbridge. these setup all have VT-d enabled. After reverting this commit, kdump is working again. So assume you need to drop this patch. Thanks Yinghai Lu
