linux-kernel - Re: [PATCH] lib/lzo: Avoid output overruns when compressing

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Message-ID: <qahmi4ozfatd4q5h4qiykinucdry6jcbee6eg4rzelyge2zmlg@norwskwechx6>
Date: Fri, 28 Feb 2025 14:24:18 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: David Sterba <dsterba@...e.cz>
Cc: Herbert Xu <herbert@...dor.apana.org.au>, 
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	Nitin Gupta <nitingupta910@...il.com>, Richard Purdie <rpurdie@...nedhand.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, "Markus F.X.J. Oberhumer" <markus@...rhumer.com>, 
	Dave Rodgman <dave.rodgman@....com>
Subject: Re: [PATCH] lib/lzo: Avoid output overruns when compressing

On (25/02/26 14:00), David Sterba wrote:
> What strikes me as alarming that you insert about 20 branches into a
> realtime compression algorithm, where everything is basically a hot
> path.  Branches that almost never happen, and never if the output buffer
> is big enough.
> 
> Please drop the patch.

David, just for educational purposes, there's only safe variant of lzo
decompression, which seems to be doing a lot of NEED_OP (HAVE_OP) adding
branches and so on, basically what Herbert is adding to the compression
path.  So my question is - why NEED_OP (if (!HAVE_OP(x)) goto output_overrun)
is a no go for compression, but appears to be fine for decompression?