From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C45DEC54F4C for ; Tue, 28 Jul 2026 05:18:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=SxU95iAD4hAuFqCDuuTVioyElcmVYzI9Vuh1mDjodCs=; b=K91sQbDqxYmw5/p3aNRJ3qtQ1E wowCWwnFWb8lI06R8Xm5vfSOXCeT1gsoNUf0Bom1ap92sZpIwfSvST5X91MevinErshcUjF6N/vzM vbk0BfQ4ljsrHqHEGOH3jZlBDvyC0cfRzt0JayoxgzwyvQTn/me7sN+XF6iOMiMHO5FGY63W7bVS2 G2jN4AKr4GcGw+EQle6gZnShI3nhbgJ1Jj+peG/7BRIkcIDjqlEq2phd2VIX4/ovtH3uue5p4Cx3z 3jRHPS7Y16dOcWjvhXZMSE0GdA3h5LQM30ZRpMLGtmkkqD4sgV7nHBuZ9qlH1fTk1SsX1s3iD4UkC zBfGFkMQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1woaDG-00000004Qu2-3PIH; Tue, 28 Jul 2026 05:18:46 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1woaDD-00000004Qtd-1a1c for linux-nvme@lists.infradead.org; Tue, 28 Jul 2026 05:18:44 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 0B55D68AFE; Tue, 28 Jul 2026 07:18:39 +0200 (CEST) Date: Tue, 28 Jul 2026 07:18:38 +0200 From: Christoph Hellwig To: Greg Kroah-Hartman Cc: Keith Busch , Hari Mishal , Jens Axboe , Christoph Hellwig , Sagi Grimberg , Hannes Reinecke , Kanchan Joshi , Nitesh Shetty , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] nvme: drop WARN_ON_ONCE on write_stream bounds check Message-ID: <20260728051838.GA20593@lst.de> References: <20260725135111.14041-1-harimishal1@gmail.com> <20260725135111.14041-3-harimishal1@gmail.com> <2026072748-unpopular-onlooker-4a2b@gregkh> <2026072849-uproar-aqua-07c3@gregkh> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2026072849-uproar-aqua-07c3@gregkh> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260727_221843_725707_8F418008 X-CRM114-Status: GOOD ( 45.86 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Tue, Jul 28, 2026 at 07:15:28AM +0200, Greg Kroah-Hartman wrote: > On Mon, Jul 27, 2026 at 04:51:40PM -0600, Keith Busch wrote: > > On Mon, Jul 27, 2026 at 09:19:27PM +0200, Greg Kroah-Hartman wrote: > > > On Mon, Jul 27, 2026 at 08:24:40AM -0600, Keith Busch wrote: > > > > On Sat, Jul 25, 2026 at 03:51:11PM +0200, Hari Mishal wrote: > > > > > write_stream is validated against bdev_max_write_streams() in both > > > > > generic block direct I/O (block/fops.c) and F2FS before a bio > > > > > carrying it is ever built, so write_stream > nr_plids shouldn't be > > > > > reachable through any current legitimate path. The remaining users > > > > > of bio->bi_write_stream elsewhere in the block layer only copy an > > > > > already-validated value between bios (bio.c, blk-crypto-fallback.c) > > > > > or compare it for merge eligibility (blk-merge.c); none of them > > > > > introduce a new, unvalidated value. > > > > > > > > > > Using WARN_ON_ONCE as the backstop for that assumption isn't worth > > > > > it given how many deployed systems run with panic-on-warn enabled; > > > > > the existing graceful return BLK_STS_INVAL already handles it on > > > > > its own. > > > > > > > > That's not a very good reason to remove a WARN_ON. You've left the check > > > > in for a condition that should never happen, so when it does happen, > > > > it'll be impossible to debug without the WARN. > > > > > > > > And the WARN also annotates the branch as unlikely, which is desirable > > > > for this case. > > > > > > But, if it ever does happen, a WARN_ON will reboot the box, given that > > > billions of Linux systems have panic-on-warn enabled. > > > > So WARN_ON is the new BUG_ON now? > > It has been that way since syzbot started sending us reports (i.e. for > many many years...) > > > If the condition happens we need to > > know how we got here and make it obvious something is wrong. So I guess > > we'd have to replace every one of these: > > > > if (WARN_ON_ONCE(condition)) ... > > > > With an open-coded version like: > > > > if (unlikely(condition)) { > > do_once(dump_stack()); > > ... > > } > > > > ? > > Yes, if userspace can trigger this. Because again, this will cause a > box to reboot. > > If we didn't have panic-on-warn, a ton of CVEs would just disappear > tomorrow. But that's not the world we live in :( > > > That doesn't seem right, so if that is the suggestion, then I think we > > need a new macro to provide the result that the WARN_ON usage expected. > > You can provide a tracedump if you really need/want it, no need to call > WARN_ON(), the macro is there for you to use. > > > > So if this can ever happen, > > > > But it can't ever happen. This patch's commit message reasoned that as > > justification to remove the warn, but we need to know how we got here > > when it does happen because it means somebody broke contract. > > Fair enough, but note that if userspace can trigger this, it should be > fixed up. See the other WARN_ON patch fix for nvme that I sent yesterday > for an example of userspace being able to trigger this type of issue: > https://lore.kernel.org/r/20260727-nvme-tcp-v1-1-61c0e36763eb@linuxfoundation.org > > > > just properly handle it and recover and don't loose user > > > data. > > > > We can't save the data from this specific condition: the data from the > > request is unwritable and lost. We've also learned that EINVAL errors > > are not handled for many DM stacking drivers in very bad ways, so again, > > we need to know how we got here when something breaks the API contract > > otherwise it'll be a difficult problem to debug without that visibility. > > Ok, if you want to keep this here, that's fine, because you know you > can't recover properly and crashing the system is the only acceptable > thing to do. But in that case, why not make it a BUG_ON()? Because we don't want a BUG_ON. If you set panic on warn in anything but a debug setup you get what you pay for, and I'm really tired of all these totally stupid attempts to make WARN_ON the new BUG_ON. It is not, and that's for a reason.