bin/111101: commit references a PR

dfilter service dfilter at
Fri Oct 12 08:00:10 PDT 2007

The following reply was made to PR bin/111101; it has been noted by GNATS.

From: dfilter at FreeBSD.ORG (dfilter service)
To: bug-followup at
Subject: Re: bin/111101: commit references a PR
Date: Fri, 12 Oct 2007 14:57:04 +0000 (UTC)

 csjp        2007-10-12 14:56:52 UTC
   FreeBSD src repository
   Modified files:
     usr.bin/lockf        lockf.1 lockf.c 
   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
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