Date: Tue, 2 Jun 2009 06:55:32 +0000 (UTC) From: Jeff Roberson <jeff@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r193301 - head/sys/kern Message-ID: <200906020655.n526tWQH005450@svn.freebsd.org>
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Author: jeff Date: Tue Jun 2 06:55:32 2009 New Revision: 193301 URL: http://svn.freebsd.org/changeset/base/193301 Log: - Use an acquire barrier to increment f_count in fget_unlocked and remove the volatile cast. Describe the reason in detail in a comment. Discussed with: bde, jhb Modified: head/sys/kern/kern_descrip.c Modified: head/sys/kern/kern_descrip.c ============================================================================== --- head/sys/kern/kern_descrip.c Tue Jun 2 05:13:02 2009 (r193300) +++ head/sys/kern/kern_descrip.c Tue Jun 2 06:55:32 2009 (r193301) @@ -2075,9 +2075,13 @@ fget_unlocked(struct filedesc *fdp, int count = fp->f_count; if (count == 0) continue; - if (atomic_cmpset_int(&fp->f_count, count, count + 1) != 1) + /* + * Use an acquire barrier to prevent caching of fd_ofiles + * so it is refreshed for verification. + */ + if (atomic_cmpset_acq_int(&fp->f_count, count, count + 1) != 1) continue; - if (fp == ((struct file *volatile*)fdp->fd_ofiles)[fd]) + if (fp == fdp->fd_ofiles[fd]) break; fdrop(fp, curthread); }
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