+.SH バグ
+According to POSIX.1\-2008/SUSv4 Section XSI 2.9.7 ("Thread Interactions with
+Regular File Operations"):
+
+.RS 4
+All of the following functions shall be atomic with respect to each other in
+the effects specified in POSIX.1\-2008 when they operate on regular files or
+symbolic links: ...
+.RE
+
+.\" http://thread.gmane.org/gmane.linux.kernel/1649458
+.\" From: Michael Kerrisk (man-pages <mtk.manpages <at> gmail.com>
+.\" Subject: Update of file offset on write() etc. is non-atomic with I/O
+.\" Date: 2014-02-17 15:41:37 GMT
+.\" Newsgroups: gmane.linux.kernel, gmane.linux.file-systems
+.\" commit 9c225f2655e36a470c4f58dbbc99244c5fc7f2d4
+.\" Author: Linus Torvalds <torvalds@linux-foundation.org>
+.\" Date: Mon Mar 3 09:36:58 2014 -0800
+.\"
+.\" vfs: atomic f_pos accesses as per POSIX
+Among the APIs subsequently listed are \fBwrite\fP() and \fBwritev\fP(2). And
+among the effects that should be atomic across threads (and processes) are
+updates of the file offset. However, on Linux before version 3.14, this was
+not the case: if two processes that share an open file description (see
+\fBopen\fP(2)) perform a \fBwrite\fP() (or \fBwritev\fP(2)) at the same time, then
+the I/O operations were not atomic with respect updating the file offset,
+with the result that the blocks of data output by the two processes might
+(incorrectly) overlap. This problem was fixed in Linux 3.14.