Date: Wed, 16 Jun 2004 12:38:18 +0900 From: Jun Kuriyama <kuriyama@imgsrc.co.jp> To: Frode Nordahl <frode@nordahl.net> Cc: Kirk McKusick <mckusick@beastie.mckusick.com> Subject: Re: UFS snapshot deadlocks Message-ID: <7moenk9npx.wl@black3.imgsrc.co.jp> In-Reply-To: <B25DE1CD-B638-11D8-B9FB-000A95A9A574@nordahl.net> References: <B25DE1CD-B638-11D8-B9FB-000A95A9A574@nordahl.net>
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At Fri, 4 Jun 2004 15:06:55 +0000 (UTC),
Frode Nordahl wrote:
> tty1:
> while (1)
> ls -la /usr/.snap
> end
>
> tty2:
> dump -0af /some/where -C 32 -L /dev/ad0s1f
I did diagnose about this.
L1. ls(1) issues lstat(2) during walking inside directory.
L2. lstat(2) calls namei().
L3. namei() tries to lock VREG /usr/.snap/dump_snapshot after locking
VDIR /usr/.snap.
D1. dump(8) calls mount(2) via mksnap_ffs(8).
D2. mount(2) calls ffs_snapshot().
D3. ffs_snapshot() locks /usr/.snap/dump_snapshot after VOP_CREATE().
D4. ffs_snapshot() searches active but unlinked files from
mnt_nvnodelist.
D5. when it founds /usr/.snap vnode, tries to lock it.
My question is:
1. should ordering of such locks be parent dir vnode first, and file
in that dir vnode second?
2. is comparing vnode pointer like this to skip /usr/.snap safe?
Index: ffs_snapshot.c
===================================================================
RCS file: /home/ncvs/src/sys/ufs/ffs/ffs_snapshot.c,v
retrieving revision 1.81
diff -u -r1.81 ffs_snapshot.c
--- ffs_snapshot.c 16 Jun 2004 00:26:30 -0000 1.81
+++ ffs_snapshot.c 16 Jun 2004 03:34:44 -0000
@@ -424,6 +424,11 @@
MNT_ILOCK(mp);
continue;
}
+ if (xvp == nd.ni_dvp) {
+ VI_UNLOCK(xvp);
+ MNT_ILOCK(mp);
+ continue;
+ }
if (vn_lock(xvp, LK_EXCLUSIVE | LK_INTERLOCK, td) != 0) {
MNT_ILOCK(mp);
goto loop;
I did repeated test like as Frode did, but I cannot see any deadlocks
after this patch.
--
Jun Kuriyama <kuriyama@imgsrc.co.jp> // IMG SRC, Inc.
<kuriyama@FreeBSD.org> // FreeBSD Project
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