git: kernel - Fix very annoying lockup (SMP)

Matthew Dillon dillon at
Tue Jan 11 14:42:36 PST 2011

commit cfaeae2ac9bf2ac78367308f7070d4a11c1680d2
Author: Matthew Dillon <dillon at>
Date:   Tue Jan 11 14:36:24 2011 -0800

    kernel - Fix very annoying lockup (SMP)
    * Fix an extremely annoying lockup that took a week+ to find.  The cpusync
      code is rather fragile and any for (;;) or while (1) style loops in the
      kernel can trip it up and cause a deadlock.  These loops are careful to
      call lwkt_process_ipiq() to ensure that cpusync processing occurs.
      However, there is a race in the LWKT thread migration code where a thread
      deschedules itself on one cpu and schedules itself on another via a remote
      ipi.  The target cpu expects the thread's TDF_RUNNING state to clear and
      will loop until that happens.
      An IPI could sneak itself into the deschedule/lwkt_switch() path and
      deadlock against a cpusync, preventing the thread from leaving the
      TDF_RUNNING state.
      The solution is to ensure that lwkt_process_ipiq() is *NOT* run in
      the lwkt_switch() path if the calling thread has descheduled itself.
    * The original bug could be reproduced by running blogbench in one window
      and a while (1) ps axl shell script in another.
    * Add DEBUG_PUSH_INFO(msg)/DEBUG_POP_INFO() macros which record (msg)
      in the globaldata structure as a debugging aid.
    * Remove unused platform/pc64/x86_64/systimer.c file.  The entire contents
      of this file was #ifdef'd out and its functionality is handled elsewhere
      by the lapic timer code.
    * #if 0 out numerous debugging bits but don't remove the code because it
      is extremely useful for finding lockup conditions.

Summary of changes:
 sys/kern/kern_ktr.c                   |    4 +
 sys/kern/lwkt_ipiq.c                  |   52 ++++++++++++++++
 sys/kern/lwkt_thread.c                |   48 ++++++++++-----
 sys/platform/pc32/apic/mpapic.c       |    4 +
 sys/platform/pc32/i386/pmap.c         |    2 +
 sys/platform/pc32/i386/pmap_inval.c   |    2 +
 sys/platform/pc64/apic/mpapic.c       |   54 +++++++++++++---
 sys/platform/pc64/conf/files          |    1 -
 sys/platform/pc64/x86_64/pmap.c       |    2 +
 sys/platform/pc64/x86_64/pmap_inval.c |    2 +
 sys/platform/pc64/x86_64/systimer.c   |  109 ---------------------------------
 sys/sys/globaldata.h                  |   26 ++++++++-
 12 files changed, 168 insertions(+), 138 deletions(-)
 delete mode 100644 sys/platform/pc64/x86_64/systimer.c

DragonFly BSD source repository

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