linux-kernel - Time nonlinearity (gettimeofday vs. mtime)

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Message-ID: <1259328678.27675.539.camel@kiste>
Date:	Fri, 27 Nov 2009 14:31:18 +0100
From:	Matthias Urlichs <matthias@...ichs.de>
To:	linux-kernel@...r.kernel.org
Subject: Time nonlinearity (gettimeofday vs. mtime)

Lately I've seen this ugliness:

13:39:06.000313 clock_gettime(CLOCK_REALTIME, {1259325546, 341196}) = 0 <0.000010>
13:39:06.000685 mkdir("/var/tmp/CP_FileTest_TempFolder_d0AOiP/tempFolder1", 0777) = 0 <0.000043>
13:39:06.000973 stat64("/var/tmp/CP_FileTest_TempFolder_d0AOiP/tempFolder1", {st_dev=makedev(252, 2), st_ino=1919104, st_mode=S_IFDIR|0755, st_nlink=2, st_uid=501, st_gid=501, st_blksize=4096, st_blocks=8, st_size=4096, st_atime=2009/11/27-13:39:05, st_mtime=2009/11/27-13:39:05, st_ctime=2009/11/27-13:39:05}) = 0 <0.000015>

This strace says that st.st_mtime is smaller than time.tv_sec even though the time was acquired earlier.
Apparently, the problem is that ext3 uses a cached time value for performance.

Question: Is there a reason that the cached time is not updated every time somebody calls gettimeofday() or clock_gettime()?
Or did just that nobody notice this problem yet?

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