Date: Wed, 28 Sep 2011 19:19:52 -0700 From: Garrett Cooper <yanegomi@gmail.com> To: Kostik Belousov <kostikbel@gmail.com> Cc: Kirk McKusick <mckusick@mckusick.com>, freebsd-fs@freebsd.org, Xin LI <delphij@freebsd.org>, bug-followup@freebsd.org Subject: Re: PR kern/161016 Need to force sync(2) before umounting UFS1 filesystems? Message-ID: <CAGH67wR4CcOuM8xKZMAX6uaZyanTt726Z7uey_i7KM00EG%2B%2BtA@mail.gmail.com> In-Reply-To: <20110929013635.GG1511@deviant.kiev.zoral.com.ua> References: <CAGH67wSvpmdmCFKxAsgLD5cGc=WcYpX=dXBkhqkePNxVNjR4=g@mail.gmail.com> <201109280019.p8S0JVUW067163@chez.mckusick.com> <20110929013635.GG1511@deviant.kiev.zoral.com.ua>
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On Wed, Sep 28, 2011 at 6:36 PM, Kostik Belousov <kostikbel@gmail.com> wrote: > On Tue, Sep 27, 2011 at 05:19:31PM -0700, Kirk McKusick wrote: >> > Date: Sun, 25 Sep 2011 12:07:18 -0700 >> > From: Garrett Cooper <yanegomi@gmail.com> >> > To: lev@freebsd.org >> > Cc: freebsd-fs@freebsd.org, Xin LI <delphij@freebsd.org>, current@freebsd.org >> > Subject: Re: Need to force sync(2) before umounting UFS1 filesystems? >> > >> > 2011/9/25 Lev Serebryakov <lev@freebsd.org>: >> > > Hello, Garrett. >> > > You wrote 25 =D3=C5=CE=D4=D1=C2=D2=D1 2011 =C7., 12:06:05: >> > > >> > >> =9A =9A Talking to Xin yesterday, he was convinced that this was a >> > >> filesystem//kern bug. Before I file a PR, I'm wondering if anyone else >> > >> has seen this issue.. >> > > =9AYes, and I posted message about it in embedded@ (Message-ID >> > > <1175277342.20110821215629@serebryakov.spb.ru>), I've got additional >> > > question from Warner Losh about base (underlying) file system, without >> > > any additional reaction. >> > >> > Thanks for the comments Adrian and Lev! I've filed PR 161016 to track >> > the issue, because it might be due to changes in the SU code, md, or a >> > subtle race condition in umount (highly unlikely, but it's been >> > noted). >> > -Garrett >> > _______________________________________________ >> > freebsd-fs@freebsd.org mailing list >> > http://lists.freebsd.org/mailman/listinfo/freebsd-fs >> > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" >> >> I have taken responsibility for working on this bug report (PR kern/161016). >> >> I propose the following change to correct it: >> >> Index: sys/kern/vfs_mount.c >> =================================================================== >> --- sys/kern/vfs_mount.c (revision 225807) >> +++ sys/kern/vfs_mount.c (working copy) >> @@ -1227,18 +1227,6 @@ >> mp->mnt_kern_flag |= MNTK_UNMOUNTF; >> error = 0; >> if (mp->mnt_lockref) { >> - if ((flags & MNT_FORCE) == 0) { >> - mp->mnt_kern_flag &= ~(MNTK_UNMOUNT | MNTK_NOINSMNTQ | >> - MNTK_UNMOUNTF); >> - if (mp->mnt_kern_flag & MNTK_MWAIT) { >> - mp->mnt_kern_flag &= ~MNTK_MWAIT; >> - wakeup(mp); >> - } >> - MNT_IUNLOCK(mp); >> - if (coveredvp) >> - VOP_UNLOCK(coveredvp, 0); >> - return (EBUSY); >> - } >> mp->mnt_kern_flag |= MNTK_DRAINING; >> error = msleep(&mp->mnt_lockref, MNT_MTX(mp), PVFS, >> "mount drain", 0); >> >> The things to check for are: >> >> 1) That it fixes the EBUSY on unmount. >> >> 2) That it does not cause unmount to hang. >> >> I would appreciate feedback as to whether this fix helps. > > I think the item 2) should be tested mostly on the hung NFS server. > > I understand what you are doing, you do not want a transient mount point > busy caller to fail the unmount. But my belief is that this is the > intended mode of operation for non-forced unmounts. > > As I compare the original bug report and your change, the reason that > UFS gives spurious EBUSY on soft unmounts is that SU code busies mp > around some processing. Is my guess right ? Then, restoring some amount > of sync(2) before the unmount would be useful, please see r222466 for > the most likely reason why the issue appeared. > > Might be, the best route would be to add a kludge mnt_flag that request > dounmount() to do a VFS_SYNC() before checking for the busy holder ? This would undo some of the changes attillio added for the locking stuff in r184554. Not sure what the prior behavior was because I only traced back the change a little bit. Thanks, -Garrett 1. http://svnweb.freebsd.org/base/head/sys/kern/vfs_mount.c?revision=184554&view=markup
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