git: kernel - Fix MP race in sysv semaphore code

Matthew Dillon dillon at
Wed Jul 11 15:36:34 PDT 2012

commit ead166eb4dd3c39eebe6407577f577dee061c743
Author: Matthew Dillon <dillon at>
Date:   Wed Jul 11 15:29:55 2012 -0700

    kernel - Fix MP race in sysv semaphore code
    * Fix a serious MP race in the sysv semaphore code due to a lack of
      protection of the semu* global structures.
    * The race occurs during semaphore allocation and deallocation vs ANY
      exiting process (even if it does not use semaphores), potentially
      leading to a live-lock in the semu_list scan code.
      The live-lock will prevent the cpu it occurs on from being able to
      switch to another kernel or user thread.  In the sample case it
      stopped pagedaemon from running, creating a backlog in the I/O
      subsystem which locked the computer up.
    Reported-by: Peter Avalos

Summary of changes:
 sys/kern/sysv_sem.c |   86 +++++++++++++++++++++++++++++++++++----------------
 1 files changed, 59 insertions(+), 27 deletions(-)

DragonFly BSD source repository

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