Date: Sun, 4 Jul 2004 12:03:39 -0400 From: Brian Fundakowski Feldman <green@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/vm uma_core.c Message-ID: <20040704160339.GA997@green.homeunix.org> In-Reply-To: <200407041559.i64FxPpj048980@repoman.freebsd.org> References: <200407041559.i64FxPpj048980@repoman.freebsd.org>
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On Sun, Jul 04, 2004 at 03:59:25PM +0000, Brian Feldman wrote: > green 2004-07-04 15:59:25 UTC > > FreeBSD src repository > > Modified files: > sys/vm uma_core.c > Log: > Reextend the M_WAITOK-disabling-hack to all three of the mbuf-related > zones, and do it by direct comparison of uma_zone_t instead of strcmp. > > The mbuf subsystem used to provide M_TRYWAIT/M_DONTWAIT semantics, but > this is mostly no longer the case. M_WAITOK has taken over the spot > M_TRYWAIT used to have, and for mbuf things, still may return NULL if > the code path is incorrectly holding a mutex going into mbuf allocation > functions. > > The M_WAITOK/M_NOWAIT semantics are absolute; though it may deadlock > the system to try to malloc or uma_zalloc something with a mutex held > and M_WAITOK specified, it is absolutely required to not return NULL > and will result in instability and/or security breaches otherwise. > There is still room to add the WITNESS_WARN() to all cases so that > we are notified of the possibility of deadlocks, but it cannot change > the value of the "badness" variable and allow allocation to actually > fail except for the specialized cases which used to be M_TRYWAIT. Any subsequent desire to change the semantics of malloc(9) or uma_zalloc(9) in the M_WAITOK case, such as this, absolutely must be taken up with the Security Officer. -- Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\ <> green@FreeBSD.org \ The Power to Serve! \ Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\
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