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Re: kern/1354 union FS can deadlock
The following reply was made to PR kern/1354; it has been noted by GNATS.
From: David Holland <dholland%netbsd.org@localhost>
Subject: Re: kern/1354 union FS can deadlock
Date: Tue, 28 Jun 2016 03:39:54 +0000
From: "J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>
Cc: David Holland <dholland%netbsd.org@localhost>
Subject: PR/1354 union FS can deadlock
Date: Mon, 27 Jun 2016 11:04:32 +0200
Should be fixed by Rev 1.43 of sys/miscfs/union/union_vnops.c:
date: 1999-03-22 18:24:22 +0100; author: sommerfe; state: Exp; lines: +17 -4;
vinvalbuf, called from vclean, could cause a locking-against-self
deadlock in VOP_FSYNC() if the unreferenced vnode picked for
reclamation happened to be stacked on top of a vnode the process
already had locked. This could happen if the same filesystem was
accessed both through a union mount and directly; it seemed to happen
most frequently when the direct access was through NFS.
Avoid this deadlock by changing vinvalbuf to pass a new FSYNC_RECLAIM
flag bit to VOP_FSYNC() to indicate that a reclaim is in progress and
only a `shallow' fsync is necessary.
Do nothing in *_fsync() in umapfs, nullfs, and unionfs when
FSYNC_RECLAIM is set; the underlying vnodes will shortly be released
in *_reclaim and may be reclaimed (and fsync'ed) later.
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig (Germany)
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