linux-kernel - Why generic_fillattr() is not protected with a lock?

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Date:	Thu, 24 Aug 2006 22:08:20 -0400
From:	"Xin Zhao" <uszhaoxin@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Why generic_fillattr() is not protected with a lock?

Hi,

I noticed that almost all local disk file systems use the default
vfs_getattr()->generic_fillattr() to get file attributes. However,
vfs_getattr()->generic_fillattr() is not protected by a lock. Is this
problematic?

Suppose process A is getting file attributes, after it read the
"mtime" and before it read the i_size, the process is scheduled out,
and another process B cuts in, change the file, and cause the change
on file size. After A is switched back, it goes ahead to read the rest
fields. Now it will have an old "mtime" but a new "i_size".

Is this scenario possible? If so, will this cause serious problem to
the file system?

Thanks,
Xin
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