git: kernel - Fix umtx (pthread_mutex etc) race in kernel

[Matthew Dillon]

commit efbd013239d66d591bfbc71ed58d36141e70b76c
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date:   Wed Jun 6 08:29:37 2018 -0700

    kernel - Fix umtx (pthread_mutex etc) race in kernel
    
    * The umtx code could still race a fork despite the wakeup
      due to certain access paths leading into umtx_sleep() only
      issuing reads, thus not triggering a COW operation post-fork.
      This results in a loss of the interlock.
    
    * Fix the issue by having umtx_sleep() fetch the user data
      with a read-modify-write instead of a read.  It now essentially
      does a lock xadd, adding $0 to the memory to force a write
      fault if necessary.
    
    * Fixes 'go' tests and probably other situations that can arise
      when heavily threaded programs use fork/exec.
    
    Reported-by: Tim Darby (+testing)

Summary of changes:
 lib/libc/sys/umtx.2  |  7 ++++++-
 sys/kern/kern_umtx.c | 54 +++++++++++++++++++++++++++++++++-------------------
 2 files changed, 40 insertions(+), 21 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/efbd013239d66d591bfbc71ed58d36141e70b76c


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