Date: Sat, 7 Aug 2004 22:33:21 -0700 From: Alfred Perlstein <alfred@freebsd.org> To: Kris Kennaway <kris@obsecurity.org> Cc: John Baldwin <jhb@FreeBSD.org> Subject: Re: cvs commit: src/sys/i386/i386 pmap.c src/sys/kern subr_witness.c Message-ID: <20040808053321.GD57908@elvis.mu.org> In-Reply-To: <20040808042703.GA64746@xor.obsecurity.org> References: <200408042031.i74KVKUf039025@repoman.freebsd.org> <200408041634.03998.jhb@FreeBSD.org> <20040808042703.GA64746@xor.obsecurity.org>
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* Kris Kennaway <kris@obsecurity.org> [040807 21:28] wrote: > On Wed, Aug 04, 2004 at 04:34:03PM -0400, John Baldwin wrote: > > On Wednesday 04 August 2004 04:31 pm, John Baldwin wrote: > > > jhb 2004-08-04 20:31:19 UTC > > > > > > FreeBSD src repository > > > > > > Modified files: > > > sys/i386/i386 pmap.c > > > sys/kern subr_witness.c > > > Log: > > > Remove a potential deadlock on i386 SMP by changing the lazypmap ipi and > > > spin-wait code to use the same spin mutex (smp_tlb_mtx) as the TLB ipi > > > and spin-wait code snippets so that you can't get into the situation of > > > one CPU doing a TLB shootdown to another CPU that is doing a lazy pmap > > > shootdown each of which are waiting on each other. With this change, > > > only one of the CPUs would do an IPI and spin-wait at a time. > > > > Both this patch and the previous I have tested locally and also sent out to > > current@ for testing. However, I received zero feedback (not even useless > > feedback), so they may theoretically be risky. > > Isn't this the patch I tested for you and reported that it did not fix > the problem? Y'know there's some existing research on these sort of low level deadlocks, ie. how to do TLB shootdown without deadlock in: "UNIX Internals: The New Frontiers" -- - Alfred Perlstein - Research Engineering Development Inc. - email: bright@mu.org cell: 408-480-4684
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