netdev - Re: rhashtable issue

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Message-ID: <vktksfdmraua3wj5zxilaawkgthyia4lrnzkbljcmj76erspuo@aqvun3mnwnsg>
Date: Tue, 26 Nov 2024 20:32:00 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: NeilBrown <neilb@...e.de>, Thomas Graf <tgraf@...g.ch>, 
	netdev@...r.kernel.org
Subject: Re: rhashtable issue - -EBUSY

On Mon, Nov 25, 2024 at 08:52:16AM +0800, Herbert Xu wrote:
> On Sun, Nov 24, 2024 at 06:58:12PM -0500, Kent Overstreet wrote:
> >
> > Sorry for claiming this was your bug - I do agree with Neal that the
> > rhastable code could handle this situation better though, so as to avoid
> > crazy bughunts.
> 
> Yes it could certainly make this more obvious.  How about a
> WARN_ON_ONCE if we detect two identical keys? That should have
> made this more obvious.

The keys aren't identical - and if they were, that would be -EEXIST;
it's the hash function that was bad (in an intentional way).

The way to detect and possibly handle this would be when rehash (perhaps
two or three rehashes in a loop) fails to reduce the longest chain
length