Date: Tue, 15 Aug 2006 12:01:26 -0400 From: John Baldwin <jhb@freebsd.org> To: Divacky Roman <xdivac02@stud.fit.vutbr.cz> Cc: Roman Divacky <rdivacky@freebsd.org>, Perforce Change Reviews <perforce@freebsd.org> Subject: Re: PERFORCE change 104029 for review Message-ID: <200608151201.27169.jhb@freebsd.org> In-Reply-To: <20060815154956.GB60482@stud.fit.vutbr.cz> References: <200608151407.k7FE7Lj5095567@repoman.freebsd.org> <200608151127.54902.jhb@freebsd.org> <20060815154956.GB60482@stud.fit.vutbr.cz>
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On Tuesday 15 August 2006 11:49, Divacky Roman wrote: > On Tue, Aug 15, 2006 at 11:27:54AM -0400, John Baldwin wrote: > > On Tuesday 15 August 2006 10:07, Roman Divacky wrote: > > > http://perforce.freebsd.org/chv.cgi?CH=104029 > > > > > > Change 104029 by rdivacky@rdivacky_witten on 2006/08/15 14:06:41 > > > > > > Protect against racing concurent creation in futex_get() > > > > > > Pointed out by: jhb > > > > > > Affected files ... > > > > > > .. //depot/projects/soc2006/rdivacky_linuxolator/compat/linux/linux_futex.c#24 > > edit > > > > > > Differences ... > > > > > > > > ==== //depot/projects/soc2006/rdivacky_linuxolator/compat/linux/linux_futex.c#24 > > (text+ko) ==== > > > > > > @@ -342,13 +342,13 @@ > > > if (locked == FUTEX_UNLOCKED) > > > FUTEX_UNLOCK; > > > > > > + if (locked == FUTEX_UNLOCKED) > > > + FUTEX_LOCK; > > > > Looks like you should collapse the lock/unlock. However, it's probably best > > to use mutexes instead of sx locks, and to instead do something like this: > > the lock here IS a mutex... > > > lock(); > > if (item in list) { > > item->ref++; > > unlock(); > > return (item); > > } > > unlock(); > > > > new_item = new_item(); > > > > lock(); > > if (item in list) { > > item->ref++; > > unlock(); > > free(new_item); > > return (item); > > } > > insert new_item > > new_item->ref++; > > unlock(); > > return (new_item) > > isnt this exactly what I am doing in later revision? No, you aren't doing the second 'if (item in list)' test to see if some other thread already added a futex for that uaddr and if so free the one you just created and return the one in the list instead. -- John Baldwin
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