linux-kernel - Re: nfs race condition

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Date:	Fri, 23 Oct 2015 13:42:10 +1100
From:	Neil Brown <nfbrown@...ell.com>
To:	Nicolas Parpandet <npa@....biz>, linux-kernel@...r.kernel.org
Cc:	pcoustillas <pcoustillas@....biz>
Subject: Re: nfs race condition

Nicolas Parpandet <npa@....biz> writes:

> Hello,
>
> I did some more investigations, (wireshark)
>
> The unlink of /tmp/crontab.vYPoHR/crontab is tranlated into a rename
> nfs call ? (.nfs file)

That happens if the file is still open.

>
> NFS	670	V3 READDIRPLUS Reply (Call In 731) crontab .. .
> NFS	210	V3 LOOKUP Call (Reply In 734), DH: 0x038abb3d/.nfs000000000098008a00000019
> NFS	194	V3 LOOKUP Reply (Call In 733) Error: NFS3ERR_NOENT
> NFS	254	V3 RENAME Call (Reply In 736), From DH: 0x038abb3d/crontab To DH: 0x038abb3d/.nfs000000000098008a00000019
> NFS	338	V3 RENAME Reply (Call In 735)
>
> and after, it tries to remove the directory /tmp/crontab.0wuoNx :
> NFS	198	V3 RMDIR Call (Reply In 738), DH: 0x954c28ec/crontab.0wuoNx
> NFS	222	V3 RMDIR Reply (Call In 737) Error: NFS3ERR_NOTEMPTY
>
> but the file /tmp/crontab.0wuoNx/crontab was renamed instead of being removed (nfs network, I cannot see .nfs000 file in fact),
> this prevent the removing of the directory  /tmp/crontab.0wuoNx (notempty)
>
> It seems a race condition, see "nfs silly rename" keyword, but I have
> the problem with mysql temp files, and crontab temp file (crontab -e),

I don't think it is a race condition exactly.  More of an ordering
problem.

Unlinking a file before closing it is rarely useful (sometimes it is,
but not here).

> am I the only one doing mysql and crontabs over NFS !!!?!?,

Probably.

> does anybody have a solution ?

Fix 'crontab' to close before unlinking...

Is this the Debian/Ubuntu crontab program.... it looks a bit like it,
but this bug was fixed 6 years ago.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=413962

Or use a tmpfs for /tmp/ rather than using NFS???

NeilBrown

>
>
> Regards
>
> Nicolas
>
>
> ----- Mail original -----
> De: "npa" <npa@....biz>
> À: linux-kernel@...r.kernel.org
> Cc: "pcoustillas" <pcoustillas@....biz>
> Envoyé: Dimanche 4 Octobre 2015 09:57:26
> Objet: nfs race condition
>
> Hello, 
>
> I'm doing some " crontab -e, exit with :x" on NFS mount point, 
> and there is a race condition whent removing temporary files : 
>
>
> 7701 write(2, "No modification made\n", 21) = 21 
> 7701 open("/tmp/crontab.vYPoHR", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 4 
> 7701 getdents(4, {{d_ino=73336409, d_off=1, d_reclen=24, d_name="."} {d_ino=73335455, d_off=2, d_reclen=24, d_name=".."} {d_ino=73340547, d_off=3, d_reclen=32, d_name="crontab"}}, 32768) = 80 
> 7701 unlink("/tmp/crontab.vYPoHR/crontab") = 0 
> 7701 getdents(4, {}, 32768) = 0 
> 7701 close(4) = 0 
> 7701 rmdir("/tmp/crontab.vYPoHR") = -1 ENOTEMPTY (Directory not empty) 
> 7701 write(2, "/tmp/crontab.vYPoHR: Directory n"..., 41) = 41 
> 7701 socket(PF_FILE, SOCK_DGRAM|SOCK_CLOEXEC, 0) = 4
>
> The unlink is really done after the rmdir,
> nfsv4 & nfsv3 over ipv6, so the rmdir fails and the directory isn't removed.
> I have same problem with mysql temporary files.
>
> If I mount with "nocto,noac,lookupcache=none" : same problem
> kernel version on server : 3.16.0-4-amd64 (debian8)
> kernel version on client : 2.6.32-39-pve (proxmox), same thing with 3.13.0-63-generic (ubuntu)
>
> Please answer me in CC, I'm not subscribed to the list.
>
> Regards
>
> Nicolas
> --
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