Re: fs/namei.c: Misuse of sequence counts?

From: Eric Biggers
Date: Sun Oct 12 2014 - 00:02:01 EST

On Sun, Oct 12, 2014 at 01:12:59AM +0100, Al Viro wrote:
> Huh? What's to guarantee that dentry hasn't become negative since the
> moment we'd fetched the seqcount? _That_ is the problem we are dealing
> with here - link_path_walk() relies on nd->inode being non-NULL.

Hmm, I guess that makes sense. So the code is actually verifying that the inode
is still the inode that was referenced from the current or root directory when
nd->path was set. But couldn't the problem also be solved by setting nd->inode
directly in the fs->seq retry loops? (The file descriptor case could be
'nd->inode = file_inode(f.file);'.) Then there would be no need for the extra
read_seqcount_retry() just for the inode. The patch you posted looks correct,
but I wonder if this approach would be better.
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