From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.gentoo.org (woodpecker.gentoo.org [140.211.166.183]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 550E4A93D; Sat, 7 Sep 2024 13:26:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=140.211.166.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725715577; cv=none; b=T73e2NurBEfFvoQbeSVwDb8+XS0qMRJvpNvyWVe3MKAyPv4UWVJuLQXMIXcr0Y5Zx7JmYzYm21QeGRLIK/RUCZcUikZBv6cGU0LJt13Hcfos5k735sLlHExD6+KdOGpj5+xMjVHbVpgbV1mb2YmFrVnsyKUhDpthbRPkqcOil+E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725715577; c=relaxed/simple; bh=rZWlTQC35qWRukStTjw642xQ+iZZzr40en6w7EIDDck=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=FETk0rTTeXUkJREpnAT4SUGDsMm6kH1NuC+P0WrjBqTEDi88yprL/coaC8QkPiTBpFMFUrMkvNHW0dGwZGICQcSkaxTvQ2APb0d+tRD44KD4c+fseZa9FCHpV7Pzv4jWYeQ0gBhrK/Ci9sKt0wIiGhPyIwa3zEYreHaty19pFog= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gentoo.org; spf=pass smtp.mailfrom=gentoo.org; arc=none smtp.client-ip=140.211.166.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gentoo.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gentoo.org From: Sam James To: Masahiro Yamada Cc: Nathan Chancellor , Nicolas Schier , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] fixdep: handle short reads in read_file In-Reply-To: <87y143ixdb.fsf@gentoo.org> (Sam James's message of "Sat, 07 Sep 2024 11:14:40 +0100") Organization: Gentoo References: <3132727fea08e81e834104761b5a5630d337340a.1725636560.git.sam@gentoo.org> <87y143ixdb.fsf@gentoo.org> Date: Sat, 07 Sep 2024 14:26:11 +0100 Message-ID: <87seubioi4.fsf@gentoo.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=utf-8 Content-Transfer-Encoding: quoted-printable Sam James writes: > Masahiro Yamada writes: > >> On Sat, Sep 7, 2024 at 12:29=E2=80=AFAM Sam James wrote: > > Hi Masahiro, > >>> >>> 50% or so of kernel builds within our package manager fail for me with >>> 'fixdep: read: success' because read(), for some reason - possibly ptra= ce, >>> only read a short amount, not the full size. >>> >>> Unfortunately, this didn't trigger a -Wunused-result warning because >>> we _are_ checking the return value, but with a bad comparison (it's com= pletely >>> fine for read() to not read the whole file in one gulp). >>> >>> Fixes: 01b5cbe7012fb1eeffc5c143865569835bcd405e >> >> >> Fixes: 01b5cbe7012f ("fixdep: use malloc() and read() to load dep_file >> to buffer") >> > > Ah, thanks. I'll fix that and send v2 depending on how we decide to move > forward wrt below. > >> >> I guess, another approach would be to use fread() instead of read(). >> >> Does the attached diff fix the issue too? >> >> > > Unfortunately no. It failed for me in the same way as before :( > > The man page mentions: >> On success, fread() and fwrite() return the number of items read or >> written. This number equals the number of bytes transferred only when si= ze is 1.=20=20 > > so I guess it suffers from the same pitfall. I checked POSIX & ISO C as w= ell > which says: >> If a partial element is read, its value is unspecified. > and >> The fread() function shall return the number of elements successfully >> read, which shall be less than nitems only if an error or end-of-file >> is encountered, or size is zero. > > The error reference is kind of mysterious there though. > > It kind of looks like fread *should* work. I'll send this mail and then > think about it a bit later and ask around to see if I'm missing > something obvious? OK, others disagree with my reading of fread and think it is ambiguous. With your patch, I was able to get failures albeit possibly less frequently. I'm trying my patch again in a loop now. > >> [...] > > thanks, > sam