Date: Sun, 12 Sep 2010 22:02:24 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r212506 - head/sys/nfsclient Message-ID: <alpine.BSF.2.00.1009122158380.52130@fledge.watson.org> In-Reply-To: <20100912205311.GG2465@deviant.kiev.zoral.com.ua> References: <201009121906.o8CJ68vQ002600@svn.freebsd.org> <alpine.BSF.2.00.1009122140040.52130@fledge.watson.org> <20100912205311.GG2465@deviant.kiev.zoral.com.ua>
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On Sun, 12 Sep 2010, Kostik Belousov wrote: > On Sun, Sep 12, 2010 at 09:41:46PM +0100, Robert Watson wrote: >> >> On Sun, 12 Sep 2010, Konstantin Belousov wrote: >> >>> Do not fork nfsiod directly from the vop methods. This causes LORs between >>> vnode lock and several locks needed during fork, like fd lock. >>> >>> Instead, schedule the task to be executed in the taskqueue context. We >>> still waiting for the fork to finish, but the context of the thread >>> executing the task does not make real LORs with our vnode lock. >> >> Does this actually functionally improve things, or is all this complexity >> about suppressing the lock order reversal? If we're waiting synchronously >> for the other thread to launch from the task queue, then the lock order >> reversal still exists, it's just not visible to WITNESS... If we had a >> static analysis tool that could run on lock and sleep/wakeup traces, it >> would still show a deadlock opportunity. > > As I said in commit message, the deadlock should be fixed, because the taskq > thread is executed in the kernel process that should even not have file > descriptors at all. Ah, I think I see where my misunderstanding arose: the behavior of kernel process fork is changed as a result of running in a different (specific) context, and hence never acquires the file descriptor lock class? Robert
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