Date: Fri, 05 Oct 2012 13:50:51 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: freebsd-fs@FreeBSD.org, Pawel Jakub Dawidek <pjd@FreeBSD.org> Subject: Re: panic: _sx_xlock_hard: recursed on non-recursive sx zfsvfs->z_hold_mtx[i] @ ...cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_znode.c:1407 Message-ID: <506EBB8B.2000800@FreeBSD.org> In-Reply-To: <506BFA5B.9060103@FreeBSD.org> References: <505DB4E6.8030407@smeets.im> <20120924224606.GE79077@ithaqua.etoilebsd.net> <20120925090840.GD35915@deviant.kiev.zoral.com.ua> <20120929154101.GK1402@garage.freebsd.pl> <20120930122403.GB35915@deviant.kiev.zoral.com.ua> <506BFA5B.9060103@FreeBSD.org>
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on 03/10/2012 11:42 Andriy Gapon said the following: > on 30/09/2012 15:24 Konstantin Belousov said the following: >> The postponing of the reclaim when vnode reserve goes low to the vnlru >> process does not solve anything, since you only change the recursion into >> the deadlock. >> >> I discussed an approach for this issue with avg. Basic idea is presented in >> the untested patch below. You can specify that some count of the free >> vnodes must be present for some dynamic scope, started by >> getnewvnode_reserve() function. While staying inside the reserved pool, >> getnewvnode() calls would not recurse into vnlru(). The scope is finished >> with getnewvnode_drop_reserve(). >> >> The getnewvnode_reserve() shall be called while no locks are held. >> >> What do you think ? > > Here is a patch that makes use of the getnewvnode_reserve API in ZFS: > http://people.freebsd.org/~avg/zfs-getnewvnode.diff > BTW, my impression is that this problem is a comeback of the original zfs_reclaim problem, but now in zfs_inactive (thanks to help from nullfs). So, with the approach that Kostik designed and which fixes zfs_inactive, zfs_reclaim should now be safe and should no longer require the taskqueue hack. There should never be a recursion back into ZFS via getnewvnode. -- Andriy Gapon
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