cvs commit: src/usr.bin/lockf lockf.1 lockf.c

[Christian S.J. Peron]

csjp        2007-10-12 14:56:52 UTC

  FreeBSD src repository

  Modified files:
    usr.bin/lockf        lockf.1 lockf.c 
  Log:
  Revision 1.12 of lockf.c fixed a "thundering herd" scenario when the
  lock experienced contention a number of processes would race to acquire
  lock when it was released.  This problem resulted in a lot of CPU
  load as well as locks being picked up out of order.
  
  Unfortunately, a regression snuck in which allowed multiple threads
  to pickup the same lock when -k was not used.  This could occur when
  multiple processes open a file descriptor to inode X (one process
  will be blocked) and the file is unlinked on unlock (thereby removing
  the directory entry allow another process to create a new directory
  entry for the same file name and lock it).
  
  This changes restores the old algorithm of: wait for the lock, then
  acquire lock when we want to unlink the file on exit (specifically
  when -k is not used) and keeps the new algorithm for when -k is used,
  which yields fairness and improved performance.
  
  Also, update the man page to inform users that if lockf(1) is being
  used to facilitate concurrency between a number of processes, it
  is recommended that -k be used to reduce CPU load and yeld
  fairness with regard to lock ordering.
  
  Collaborated with:      jdp
  PR:             bin/114341
  PR:             bin/116543
  PR:             bin/111101
  MFC after:      1 week
  
  Revision  Changes    Path
  1.19      +13 -1     src/usr.bin/lockf/lockf.1
  1.17      +59 -10    src/usr.bin/lockf/lockf.c