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 82B9A13A257; Thu, 8 Aug 2024 10:54:05 +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=1723114445; cv=none; b=mC1M19cAoPB2+utxGISlWdo+Rg4J9C4ThJWw7bIukKOQ5kFqo2Y6W+hwBhs0YNvs9maCQ1ZwcYaq1DHqeOSQ5jwQmSR7KF26JE0WpWg2y4lt41o2MzddWc5+O1SJjWMqldv0EtLaRg3Hvw9qXBmvobWt75mpORCHvlFd4ySpRGA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723114445; c=relaxed/simple; bh=HDK+8Ru8mrSG1BMFW4Vya3rOBikRpLbHPx8o00aMvJc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=nm6EcT7gyQkWdB0Dpemv3pzA3apGIJ0blzkKg2c279NDGnpw+CRLjQaqhfWXJTfmRhRuRI787O+S2XNaZbWD36jEFIUGvA2KaeBgDHXlYnWdRZGe6FkxeLY+InqMnapAFrnewgUgdTSbJgurzx/ymaOsikhwgT4Qz2l70a4KGqk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZKqu6KYv; 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="ZKqu6KYv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D866C32782; Thu, 8 Aug 2024 10:54:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1723114445; bh=HDK+8Ru8mrSG1BMFW4Vya3rOBikRpLbHPx8o00aMvJc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ZKqu6KYvlbkBuMXVZgkge7xyRC1nvfuDmbcNjc4YRRhKgnyEI07HY73lWgeDteHNF UgbqRqp1Fe4TvtN0hS1dtdyZc+ICvLwi2y2KmJtN2V1H3c3kSf6Os3FaAXj99P7uOZ skruFMPz2gCbEgM8wjLCJzod+4L8U2EFnxaZMaGYpq4NBEPnpQv9hpXS5IWDVGdcLb rDOwSXXr0Lxgk7DBCV1EHpJeDU7oqfLuTZH70+inPs1eQubeQHAAh0PrvuUPcmhJX9 MPnyUtPako+pKFLIchuvj9JGOt/vU1VXSdPEZLNk64+FlnoIdfdJm/lPv2Tl/pycG7 CZjewCJ8cvXZw== Message-ID: Subject: Re: [PATCH v2] fs: try an opportunistic lookup for O_CREAT opens too From: Jeff Layton To: Christian Brauner Cc: Alexander Viro , Jan Kara , Andrew Morton , Mateusz Guzik , Josef Bacik , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 08 Aug 2024 06:54:03 -0400 In-Reply-To: <20240808-karnickel-miteinander-d4fa6cd5f3c7@brauner> References: <20240806-openfast-v2-1-42da45981811@kernel.org> <20240807-erledigen-antworten-6219caebedc0@brauner> <20240808-karnickel-miteinander-d4fa6cd5f3c7@brauner> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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On Thu, 2024-08-08 at 12:36 +0200, Christian Brauner wrote: > On Wed, Aug 07, 2024 at 10:36:58AM GMT, Jeff Layton wrote: > > On Wed, 2024-08-07 at 16:26 +0200, Christian Brauner wrote: > > > > +static struct dentry *lookup_fast_for_open(struct nameidata *nd, i= nt open_flag) > > > > +{ > > > > + struct dentry *dentry; > > > > + > > > > + if (open_flag & O_CREAT) { > > > > + /* Don't bother on an O_EXCL create */ > > > > + if (open_flag & O_EXCL) > > > > + return NULL; > > > > + > > > > + /* > > > > + * FIXME: If auditing is enabled, then we'll have to unlazy to > > > > + * use the dentry. For now, don't do this, since it shifts > > > > + * contention from parent's i_rwsem to its d_lockref spinlock. > > > > + * Reconsider this once dentry refcounting handles heavy > > > > + * contention better. > > > > + */ > > > > + if ((nd->flags & LOOKUP_RCU) && !audit_dummy_context()) > > > > + return NULL; > > >=20 > > > Hm, the audit_inode() on the parent is done independent of whether th= e > > > file was actually created or not. But the audit_inode() on the file > > > itself is only done when it was actually created. Imho, there's no ne= ed > > > to do audit_inode() on the parent when we immediately find that file > > > already existed. If we accept that then this makes the change a lot > > > simpler. > > >=20 > > > The inconsistency would partially remain though. When the file doesn'= t > > > exist audit_inode() on the parent is called but by the time we've > > > grabbed the inode lock someone else might already have created the fi= le > > > and then again we wouldn't audit_inode() on the file but we would hav= e > > > on the parent. > > >=20 > > > I think that's fine. But if that's bothersome the more aggressive thi= ng > > > to do would be to pull that audit_inode() on the parent further down > > > after we created the file. Imho, that should be fine?... > > >=20 > > > See https://gitlab.com/brauner/linux/-/commits/vfs.misc.jeff/?ref_typ= e=3Dheads > > > for a completely untested draft of what I mean. > >=20 > > Yeah, that's a lot simpler. That said, my experience when I've worked > > with audit in the past is that people who are using it are _very_ > > sensitive to changes of when records get emitted or not. I don't like > > this, because I think the rules here are ad-hoc and somewhat arbitrary, > > but keeping everything working exactly the same has been my MO whenever > > I have to work in there. > >=20 > > If a certain access pattern suddenly generates a different set of > > records (or some are missing, as would be in this case), we might get > > bug reports about this. I'm ok with simplifying this code in the way > > you suggest, but we may want to do it in a patch on top of mine, to > > make it simple to revert later if that becomes necessary. >=20 > Fwiw, even with the rearranged checks in v3 of the patch audit records > will be dropped because we may find a positive dentry but the path may > have trailing slashes. At that point we just return without audit > whereas before we always would've done that audit. >=20 I don't think so. v3 has it drop out of rcuwalk and do the audit_inode call in the case of trailing slashes. I took great pains here to ensure that if we emitted a record before that we still do it after. Do let me know if I missed a case though. > Honestly, we should move that audit event as right now it's just really > weird and see if that works. Otherwise the change is somewhat horrible > complicating the already convoluted logic even more. >=20 > So I'm appending the patches that I have on top of your patch in > vfs.misc. Can you (other as well ofc) take a look and tell me whether > that's not breaking anything completely other than later audit events? That all looks fine to me. I'm not a heavy user of audit, but the change you've made seems sane to me. Hopefully no one will notice. I'll plan to do some testing with it later today. Thanks! --=20 Jeff Layton