From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3B3752FDC3D for ; Mon, 16 Mar 2026 15:06:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773673595; cv=none; b=AMXRaHRm9YCZ3FTPxdwb05vh76giACREpmeuYVNPaiWsG08ADiHCHcPqWrfv5C9xzAyGkt/AVRh+cAZ5U+rhLW1UjCxW/fKgf7dGvj3ZFga5saQOIgQK/EIq9Kr/sqpAv5zHaRTNhs32rvudFmVG8jfBXMaJGjVR8b8eiSB9J8w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773673595; c=relaxed/simple; bh=VUwHVs+S9Dc4lePhODG97FdAbzEBNXby5kox35Y5M+M=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mi9LkNH94cp0t0qxbNYqNxj3+X5eizHPt2Uv2283PMAz2NFUKg/UNsrsnqb2XmdbruomoCohjHhJTR1bExeHLdsXYO/4/uTOfkfb73N5S10bpIUX0UpS+yiXA4knMyyEymqjCqD163Pz0mbXpPdgh3hn0RquVdvCeCrjvFGk7EA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MHmz72Ic; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MHmz72Ic" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7F594C19421; Mon, 16 Mar 2026 15:06:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773673594; bh=VUwHVs+S9Dc4lePhODG97FdAbzEBNXby5kox35Y5M+M=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MHmz72IcPyhBPK1xiztRGGigxvKxQXzHFT+c+fBoNMuKIRSPimSmliZjLewO7U+qp Nl6SRrf/G9V5T5UOfp+72suPDjCMpoP7MfOIA1YNKgGTh7CTxXvr1KmWM55zGJWHf7 lGBmzyuLYlALfVmJczNKUvdCPo0mBQ+b8eodOX+qyZTlNH2EliwNzP1uUJ+FNnLXvJ dkXSc24LXROuoykfnzGbhvrTfDu8Fwk1n4Bplj1bHzxKdO2EcCyPYiTz5QWmnKMst2 bxnO4cjcB5YjvAqguH2kPgKQSS8Qd+Q3oBreHxYmAoBHe/b1CcXjlCGKOmbqNVhzpG +dNTHIA7Czbuw== Date: Mon, 16 Mar 2026 15:06:32 +0000 From: Yosry Ahmed To: "Kanchana P. Sridhar" Cc: Andrew Morton , hannes@cmpxchg.org, nphamcs@gmail.com, chengming.zhou@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, herbert@gondor.apana.org.au, senozhatsky@chromium.org Subject: Re: [PATCH 0/2] zswap pool per-CPU acomp_ctx simplifications Message-ID: References: <20260314051632.17931-1-kanchanapsridhar2026@gmail.com> <20260314171150.fd6a80a8f51a5390144d20d6@linux-foundation.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: > > > @@ -786,7 +786,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node) > > > return ret; > > > > > > acomp_ctx->acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu)); > > > - if (IS_ERR(acomp_ctx->acomp)) { > > > + if (IS_ERR_OR_NULL(acomp_ctx->acomp)) { > > Does crypto_alloc_acomp_node() ever return NULL? > > Looking at the error handling just below this check, if this were to > > actually return NULL, PTR_ERR(NULL) evaluates to 0. This would cause > > the function to incorrectly return 0 (success) instead of an error code, > > hiding the allocation failure. > > This is a good catch. Just to provide context, this patch was > introduced based on Yosry's earlier comments in [1]. > > [1]: https://patchwork.kernel.org/comment/26282128/ > > crypto_alloc_acomp_node() currently does not return NULL. However, it > could, in future. > Since the rest of zswap_cpu_comp_prepare() dereferences > acomp_ctx->acomp, it depends on whether we want to future-proof the > code to handle a possible eventuality of crypto_alloc_acomp_node() > returning NULL. Hmm upon revisiting this, I think keeping this as IS_ERR() here is a better documentation for the API, and the incossitency between this code and acomp_ctx_dealloc() is arguably documenting that the function can only return an ERR, but it can also be NULL-initialized by zswap. > > If the maintainers think future-proofing is beneficial, I would need > to handle the PTR_ERR(NULL) which would send a false success status. > If we don't think we need to handle a future NULL return from > crypto_alloc_acomp_node(), then I don't think this change is needed. > We could leave it as IS_ERR(acomp_ctx->acomp). I would like to get the > maintainers' inputs on how to proceed. > > > > acomp_ctx->req = acomp_request_alloc(acomp_ctx->acomp); > > > - if (!acomp_ctx->req) { > > > + if (IS_ERR_OR_NULL(acomp_ctx->req)) { > > Is this change necessary for acomp_request_alloc()? > > This function strictly returns NULL on allocation failure, not an error > > pointer. Changing this to IS_ERR_OR_NULL() obscures the actual API contract > > without providing a functional benefit. > > As of now, acomp_request_alloc() returns a valid "req" or NULL in case > of an error. Same question as above. The only benefit would be making > the code more robust to handle changes in the acomp API in future. For this one, do we need to do IS_ERR_OR_NULL() in acomp_ctx_dealloc() to begin with? If acomp_request_alloc() only returns NULL, maybe that should also be a NULL check? In this case, we don't really need to make any changes here, and I think this patch can just be dropped.