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Date: Fri, 21 Mar 2008 02:44:39 -1000 (HST)
From: Jeff Roberson <jroberson@chesapeake.net>
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To: Konstantin Belousov <kib@FreeBSD.org>
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Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/ufs/ffs ffs_vnops.c
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On Fri, 21 Mar 2008, Konstantin Belousov wrote:

> kib         2008-03-21 12:33:00 UTC
>
>  FreeBSD src repository
>
>  Modified files:
>    sys/ufs/ffs          ffs_vnops.c
>  Log:
>  Reduce the acquisition of the vnode interlock in the ffs_read() and
>  ffs_extread() when setting the IN_ACCESS flag by checking whether the
>  IN_ACCESS is already set. The possible race there is admissible.

I don't believe there is a race because we should always hold an exclusive 
vnode lock and the vnode interlock when clearing.  The exclusive node lock 
would prevent ffs_read() from executing entirely, so we don't have to 
worry about races with clearing the bit.  Races to set the bit are handled 
by the vnode interlock.

I should also mention that while this may seem innocuous enough this 
figured heavily in LOCK_PROFILING for a real workload.

Thanks,
Jeff

>
>  Tested by:      pho
>  Submitted by:   jeff
>
>  Revision  Changes    Path
>  1.180     +4 -2      src/sys/ufs/ffs/ffs_vnops.c
>