From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751156AbWFKMA7 (ORCPT ); Sun, 11 Jun 2006 08:00:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751172AbWFKMA7 (ORCPT ); Sun, 11 Jun 2006 08:00:59 -0400 Received: from pops.net-conex.com ([204.244.176.3]:61663 "EHLO mail.net-conex.com") by vger.kernel.org with ESMTP id S1751156AbWFKMA7 (ORCPT ); Sun, 11 Jun 2006 08:00:59 -0400 Date: Sun, 11 Jun 2006 04:54:21 -0700 From: "Robin H. Johnson" To: linux-kernel@vger.kernel.org Cc: Al Viro , linux-fsdevel@vger.kernel.org Subject: [PATCH] tmpfs time granularity fix for [acm]time going backwards. Also VFS time granularity bug on creat(). (Repost, more content) Message-ID: <20060611115421.GE26475@curie-int.vc.shawcable.net> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="JBi0ZxuS5uaEhkUZ" Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --JBi0ZxuS5uaEhkUZ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable [Please CC me on replies]. This patch should probably be included for 2.6.17, despite how long the bug has been around. It's a one-liner, with no side-effects. I noticed a strange behavior in a tmpfs file system the other day, while building packages - occasionally, and seemingly at random, make decided to rebuild a target. However only on tmpfs. A file would be created, and if checked, it had a sub-second timestamp. However, after an utimes related call where sub-seconds should be set, they were zeroed instead. In the case that a file was created, and utimes(...,NU= LL) was used on it in the same second, the timestamp on the file moved backward= s. Puesdo-code of my testcase: int fd =3D creat(name,0644); fstat(fd,&st); printf("...[acm]time...",...) futime(fd,NULL); fstat(fd,&st); printf("...[acm]time...",...) close(fd); Tested against: linus 2.6.13, linus 2.6.17-rc6. Test output from a filesystem not supporting sub-second timestamps (ext3, r= eiserfs): creat: m=3D1149891410.0 c=3D1149891410.0 a=3D1149891407.0 futimes: m=3D1149891410.0 c=3D1149891410.0 a=3D1149891410.0 Test output from a filesystem supporting sub-second timestamps (jfs,xfs,ram= fs): creat: m=3D1149891452.928796249 c=3D1149891452.928796249 a=3D1149891452.9= 28796249 futimes: m=3D1149891452.928796249 c=3D1149891452.928796249 a=3D1149891452.9= 28796249 Test output from the tmpfs filesystem before the fix: creat: m=3D1149892052.562029884 c=3D1149892052.562029884 a=3D1149892052.5= 62029884 futimes: m=3D1149892052.0 c=3D1149892052.0 a=3D1149892052.0 Test output from the tmpfs filesystem with the patch below: creat: m=3D1149892086.382150894 c=3D1149892086.382150894 a=3D1149892075.4= 73249075 futimes: m=3D1149892086.383150885 c=3D1149892086.383150885 a=3D1149892086.3= 83150885 The output above of jfs/xfs/ramfs having identical ctime/mtime in the utime/creat calls is just co-incidence, my box is reasonably fast, on a slower machine, they do diverge more. My box is just fast enough that they happened in the same tick (I have HZ=3D1000). After some digging, I found that this was being caused by tmpfs not having a time granularity set, thus inheriting the default 1s granularity. NOTE: The further bug: I believe this also indicates there is another bug at the VFS layer, where the initial timestamp from the creat() operation did not have the granularity applied to it. I haven't traced this problem down yet, others that are more familiar with the VFS might have a bit better luck. Unless this is fixed, similar issues may crop up with other filesystems. It just needs a bit of code like this: inode->i_[acm]time =3D current_fs_time(inode->i_sb); Signed-off-by: Robin H. Johnson --- mm/shmem.c +++ mm/shmem.c @@ -2102,6 +2102,7 @@ #endif sb->s_blocksize_bits =3D PAGE_CACHE_SHIFT; sb->s_magic =3D TMPFS_MAGIC; sb->s_op =3D &shmem_ops; + sb->s_time_gran =3D 1; =20 inode =3D shmem_get_inode(sb, S_IFDIR | mode, 0); if (!inode) --=20 Robin Hugh Johnson E-Mail : robbat2@gentoo.org GnuPG FP : 11AC BA4F 4778 E3F6 E4ED F38E B27B 944E 3488 4E85 --JBi0ZxuS5uaEhkUZ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2-ecc0.1.6 (GNU/Linux) Comment: Robbat2 @ Orbis-Terrarum Networks iD8DBQFEjARtPpIsIjIzwiwRAo4IAJ4tqu0KUNYRGpX5OUOQLVLPoKPyPgCeMgJm DEBSQ6NHm0mlaPIpdkmVW6Y= =zZgW -----END PGP SIGNATURE----- --JBi0ZxuS5uaEhkUZ--