Date: Fri, 18 Apr 2003 06:50:12 -0400 (EDT) From: Robert Watson <rwatson@freebsd.org> To: Terry Lambert <tlambert2@mindspring.com> Cc: Daniel Eischen <eischen@pcnet1.pcnet.com> Subject: Re: libpthread patch Message-ID: <Pine.NEB.3.96L.1030418063854.24445U-100000@fledge.watson.org> In-Reply-To: <3E9FAE89.4D656F38@mindspring.com>
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On Fri, 18 Apr 2003, Terry Lambert wrote: > You are allowed to recurse on a mutex in the kernel, because there's > some depth to code paths that shouldn't be there, but it's easier to > allow recursion than it is to correct the code. By default, mutexes are not permitted to be recursed, and recursing them will cause a panic. Recursion is only permitted if the MTX_RECURSE flag is set at mutex initialization time, which is strongly discouraged. There are several mutex in the kernel where the flag is set, but I hope to see the list remain small (and go down). A quick grep of of kern shows four classes of mutexes with MTX_RECURSE set (one is Giant), and 57 without (approximately). The IP stack locking, on the other hand, has four mutex classes, of which two permit recursion (PCB locks). Robert N M Watson FreeBSD Core Team, TrustedBSD Projects robert@fledge.watson.org Network Associates Laboratories
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