Date: Fri, 21 Mar 2008 14:53:29 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Jeff Roberson <jroberson@chesapeake.net> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/ufs/ffs ffs_vnops.c Message-ID: <20080321125329.GV10374@deviant.kiev.zoral.com.ua> In-Reply-To: <20080321125042.GU10374@deviant.kiev.zoral.com.ua> References: <200803211233.m2LCX1Bm099652@repoman.freebsd.org> <20080321024123.P910@desktop> <20080321125042.GU10374@deviant.kiev.zoral.com.ua>
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[-- Attachment #1 --] On Fri, Mar 21, 2008 at 02:50:42PM +0200, Kostik Belousov wrote: > On Fri, Mar 21, 2008 at 02:44:39AM -1000, Jeff Roberson wrote: > > 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 > We may hold only the shared vnode lock and the interlock when clearing, > in the ufs_itimes(). Forgot to note that example of the ufs_itimes() call while holding only the shared vnode lock is the ufs_getattr(). > > > 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. > Yes, the race I meant is the clearing of the IN_ACCESS while performing > unlocked read for check. It may be considered as a race, may be not. > > > > > 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 > > > [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (FreeBSD) iEUEARECAAYFAkfjr8kACgkQC3+MBN1Mb4iKdwCTBgxChDKYkl5XdRzq4FCn0Asx pQCgzXmFrUIyFqdrgN61NlFoM00bxow= =0lLd -----END PGP SIGNATURE-----
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