linux-kernel - Re: Can ovl_drop_write() be called earlier in ovl_dentry

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Message-ID: <16823.1433173503@warthog.procyon.org.uk>
Date:	Mon, 01 Jun 2015 16:45:03 +0100
From:	David Howells <dhowells@...hat.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	dhowells@...hat.com, Al Viro <viro@...iv.linux.org.uk>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>
Subject: Re: Can ovl_drop_write() be called earlier in ovl_dentry_open()

Miklos Szeredi <miklos@...redi.hu> wrote:

> > In ovl_dentry_open(), ovl_drop_write() is called after vfs_open() - but is
> > this actually necessary?  Can't we just drop it post-copyup?  After all,
> > that's all we wanted the write lock for, right?
> 
> Hmm,  that could result in a race where remount r/o of upper fs comes
> in between copy-up and vfs_open() so copy-up succeeds but the actual
> open fails.  It's harmless, though, and not  very likely.  So I guess
> your patch is OK.

That race is there anyway if there's no copy up, right?

David
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