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SubjectRe: [PATCH] vfs: make real_lookup do dentry revalidation with i_mutex held
On Tue, 17 Mar 2009, Christoph Hellwig wrote:
> Keeping i_mutes over do_revalidate seem fine from a first glance, but
> can you please do it without rearranging the whole code?

Yeah, but not without an extra goto. Holding i_mutex over revalidate is
only half of it... we also want to go ahead with the ->lookup if the
revalidate fails (instead of returning -ENOENT). I make the patch easier
to read (with a goto), but I assumed we'd want the resulting code to be
more clear?

FWIW, here's the patched result:

result = d_lookup(parent, name);
if (result) {
/*
* The cache was re-populated while we waited on the
* mutex. We need to revalidate, this time while
* holding i_mutex (to avoid another race).
*/
if (result->d_op && result->d_op->d_revalidate) {
result = do_revalidate(result, nd);
if (result)
goto out_unlock;
/*
* The dentry was left behind invalid. Just
* do the lookup.
*/
} else {
goto out_unlock;
}
}

/* Don't create child dentry for a dead directory. */
result = ERR_PTR(-ENOENT);
if (IS_DEADDIR(dir))
goto out_unlock;

dentry = d_alloc(parent, name);
result = ERR_PTR(-ENOMEM);
if (dentry) {
result = dir->i_op->lookup(dir, dentry, nd);
if (result)
dput(dentry);
else
result = dentry;
}
out_unlock:

Let me know!
sage


> Something like the tiny untested patch below should archive the same
> thing:
>
>
> Index: linux-2.6/fs/namei.c
> ===================================================================
> --- linux-2.6.orig/fs/namei.c 2009-03-17 09:15:53.430978739 +0100
> +++ linux-2.6/fs/namei.c 2009-03-17 09:16:19.553981306 +0100
> @@ -512,12 +512,12 @@ out_unlock:
> * Uhhuh! Nasty case: the cache was re-populated while
> * we waited on the semaphore. Need to revalidate.
> */
> - mutex_unlock(&dir->i_mutex);
> if (result->d_op && result->d_op->d_revalidate) {
> result = do_revalidate(result, nd);
> if (!result)
> result = ERR_PTR(-ENOENT);
> }
> + mutex_unlock(&dir->i_mutex);
> return result;
> }
>
>
>


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