Date: Wed, 24 Sep 2014 10:21:03 -0500 From: Bryan Drewery <bdrewery@FreeBSD.org> To: Peter Holm <peter@holm.cc>, Konstantin Belousov <kostikbel@gmail.com> Cc: FreeBSD FS <freebsd-fs@FreeBSD.org> Subject: Re: Deadlock with umount -f involving tmpfs on top of ZFS on r271170 Message-ID: <5422E15F.8050702@FreeBSD.org> In-Reply-To: <20140924132605.GA11772@x2.osted.lan> References: <5420D5FC.4030600@FreeBSD.org> <20140923131244.GC8870@kib.kiev.ua> <5422240F.4080003@FreeBSD.org> <20140924102758.GH8870@kib.kiev.ua> <20140924132605.GA11772@x2.osted.lan>
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[-- Attachment #1 --] On 9/24/2014 8:26 AM, Peter Holm wrote: > On Wed, Sep 24, 2014 at 01:27:58PM +0300, Konstantin Belousov wrote: >> On Tue, Sep 23, 2014 at 08:53:19PM -0500, Bryan Drewery wrote: >>> I tried your patch and still ran into the deadlock. Here is the debug >>> information: https://people.freebsd.org/~bdrewery/vfs_deadlock.2.txt >> >> I see what is going on. Previous patch cannot help there. >> >> The problem is that kern_linkat() starts write with vn_start_write(9), >> and then tries to execute namei(9) with a path potentially crossing >> the mount point. If the mount point is being unmounted, unmount cannot >> lay suspension on the filesystem due to writer, but it owns the covered >> vnode lock. On the other hand, namei(9) is unable to cross the mount >> point since covered vnode is locked, thus writer does not make progress. >> >> The similar issue exists in rename code. The deadlock is only possible >> for filesystems which suspend writes on unmount; such fs are UFS and tmpfs. >> >> Try this. >> >> diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c >> index b3b7ed5..9775480 100644 > > I had been trying different scenarios without much luck, but with > your description I got the problem instantly. :) > > The patch is an improvement, but: > > http://people.freebsd.org/~pho/stress/log/kostik718.txt > > - Peter > By the way this was my test script: http://dpaste.com/35AYZZ7 It could be simplified a lot. -- Regards, Bryan Drewery [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (MingW32) iQEcBAEBAgAGBQJUIuFiAAoJEDXXcbtuRpfP7AgIAJfRpz4TgSHCmhkV5dWjuROZ S78/01sl2VNzhK/O1dNSdVEkPmoKbTRGO9nbecLytaVqjUZk8EbbL0DEG07srDoB znXg1b8ASglw2lxqNfQ/849FvwHtHb3aDSNIALBiOctrIPngm4PgnIm5jKTaaAQJ 4j9DwTJ93d5mOw2JzaKZ0Ro7WBmCpx+D9hvfVYPo1sPbvtp5ujkRG+I92iJswq8U +3iiJYBjhFCYZmD3HBV4O7Bbvqa1w3Ip/0UPdsYhwNSlPT6wEL5ujdIcCRFanegy u7zJ+of/dS9mqq/cfc6CIyOJ1uERs9pF5fcLuRntFY//upwVmaZn58ct2uyc7rg= =FsIY -----END PGP SIGNATURE-----
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