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 008885DF06; Wed, 6 Mar 2024 09:55:47 +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=1709718948; cv=none; b=S7/aTpYpIvdpZOrUgq8rxKtu8hbzuSGz4gqDndatZJuaXkvFzIb77XTz5332f4yXDKxTvp/+7N2oSKwrefglyxUMURkhnIlg2BsBPJpVOpmWJR+cf7uLQahpjGbRTsN/dF7N/BB1v8hmT+uwIA4JkXw+xaSGm4lbIJVGzmDO4DA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709718948; c=relaxed/simple; bh=dup48kaib2L/bKU8uwW0nwMt//arxlDgChz0V2ZGaSI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NFUZ5YNxk130wrXHEqwi4WCmEXR/bjeHVw72aRCyGz48h4LecopRXqE0yAeoajwxSZbpDvieK+7rTZN720RjK/HDft0ivIMAE2HMSFsMCAfakddCY0gWuTMNAwYCzBMugnU9niwXGGPEHxQKJEjT6Vg6FEeoeVGw9y8e4lMBO+U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=InADAXEi; 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="InADAXEi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F008DC433C7; Wed, 6 Mar 2024 09:55:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1709718947; bh=dup48kaib2L/bKU8uwW0nwMt//arxlDgChz0V2ZGaSI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=InADAXEi2JGdmVGpom2KWFDDXLD42EPDneT2/ujqkJFpAyi5FqzMhg4V37dSmdb8C KylWKvqgm2Dk1LZZtt615nz+8E4o8P2Qk685RuoFUI1ABy8kFMWAFrBTSNgDCKbMIt QP1El4MMpbd1OzLNEJzJnJV+N9rCspDPRT6vOBMwEdl9TL2/PSKR+wbDSVSZJRukrO l6Keq/SHq/FoUKGlafu2yUV9emWIfdaSKb1IEgZK9j4qJdvWhAliXleMoxm1Qm2w+L hCF8O54wR0s5yWSDxelyE846fBFh4KynEWFgFBURVTzGEvg9Uzb2bCJ2fYjzcTjVCL kTNvyhEawzZJw== Date: Wed, 6 Mar 2024 10:55:43 +0100 From: Christian Brauner To: Linus Torvalds Cc: Stephen Rothwell , Tong Tiangen , Linux Kernel Mailing List , Linux Next Mailing List Subject: Re: linux-next: build warning after merge of the vfs-brauner tree Message-ID: <20240306-staufer-parklandschaft-0b0c0532ac91@brauner> References: <20240306105150.06a456da@canb.auug.org.au> <20240306153703.499661d2@canb.auug.org.au> 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=utf-8 Content-Disposition: inline In-Reply-To: On Tue, Mar 05, 2024 at 08:47:40PM -0800, Linus Torvalds wrote: > On Tue, 5 Mar 2024 at 20:37, Stephen Rothwell wrote: > > > > +static struct page *dump_page_copy(struct page *src, struct page *dst) > > +{ > > + return NULL; > > +} > > No, it needs to be "return src;" not NULL. > > That > > #define dump_page_copy(src, dst) ((dst), (src)) > > was supposed to be a "use 'dst', return 'src'" macro, and is correct > as that. The problem - as you noticed - is that it causes that "left > side of comma expression has no effect" warning. > > (Technically it *does* have an effect - exactly the "argument is used" > one - but the compiler warning does make sense). > > Actually, the simplest thing to do is probably just > > #define dump_page_free(x) ((void)(x)) > #define dump_page_copy(src, dst) (src) > > where the "use" of the 'dump_page' argument is that dump_page_free() > void cast, and dump_page_copy() simply doesn't need to use it at all. > > Christian? I would just do it like Stephen did (but returning src ofc) because it's symmetric to the #ifdef copy_mc_to_kernel definition of dump_page_copy() and seems easier to read to me. But I honestly don't care too much. So I'd pick Stephen's change and if you prefer to do it differently just change it when I send you the pr. +/* + * If we might get machine checks from kernel accesses during the + * core dump, let's get those errors early rather than during the + * IO. This is not performance-critical enough to warrant having + * all the machine check logic in the iovec paths. + */ +#ifdef copy_mc_to_kernel + +#define dump_page_alloc() alloc_page(GFP_KERNEL) +#define dump_page_free(x) __free_page(x) +static struct page *dump_page_copy(struct page *src, struct page *dst) +{ + void *buf = kmap_local_page(src); + size_t left = copy_mc_to_kernel(page_address(dst), buf, PAGE_SIZE); + kunmap_local(buf); + return left ? NULL : dst; +} + +#else + +/* We just want to return non-NULL; it's never used. */ +#define dump_page_alloc() ERR_PTR(-EINVAL) +#define dump_page_free(x) ((void)(x)) +static inline struct page *dump_page_copy(struct page *src, struct page *dst) +{ + return src; +} +#endif