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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42abe64fd90sm1530134f8f.21.2025.11.06.14.39.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Nov 2025 14:39:01 -0800 (PST) Date: Thu, 6 Nov 2025 22:39:00 +0000 From: David Laight To: Chuck Lever Cc: "stable@vger.kernel.org" , Andrew Morton , David Laight , Linux NFS Mailing List , Linux List Kernel Mailing , speedcracker@hotmail.com Subject: Re: Compile Error fs/nfsd/nfs4state.o - clamp() low limit slotsize greater than high limit total_avail/scale_factor Message-ID: <20251106223900.3893d7d9@pumpkin> In-Reply-To: <8cf5dc85-dee8-4e83-8f83-6b3411dddbee@kernel.org> References: <37bc1037-37d8-4168-afc9-da8e2d1dd26b@kernel.org> <20251106192210.1b6a3ca0@pumpkin> <8cf5dc85-dee8-4e83-8f83-6b3411dddbee@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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-Transfer-Encoding: 7bit On Thu, 6 Nov 2025 14:32:34 -0500 Chuck Lever wrote: > On 11/6/25 2:22 PM, David Laight wrote: > > On Thu, 6 Nov 2025 09:33:28 -0500 > > Chuck Lever wrote: > > > >> FYI > >> > >> https://bugzilla.kernel.org/show_bug.cgi?id=220745 > > > > Ugg - that code is horrid. > > It seems to have got deleted since, but it is: > > > > u32 slotsize = slot_bytes(ca); > > u32 num = ca->maxreqs; > > unsigned long avail, total_avail; > > unsigned int scale_factor; > > > > spin_lock(&nfsd_drc_lock); > > if (nfsd_drc_max_mem > nfsd_drc_mem_used) > > total_avail = nfsd_drc_max_mem - nfsd_drc_mem_used; > > else > > /* We have handed out more space than we chose in > > * set_max_drc() to allow. That isn't really a > > * problem as long as that doesn't make us think we > > * have lots more due to integer overflow. > > */ > > total_avail = 0; > > avail = min((unsigned long)NFSD_MAX_MEM_PER_SESSION, total_avail); > > /* > > * Never use more than a fraction of the remaining memory, > > * unless it's the only way to give this client a slot. > > * The chosen fraction is either 1/8 or 1/number of threads, > > * whichever is smaller. This ensures there are adequate > > * slots to support multiple clients per thread. > > * Give the client one slot even if that would require > > * over-allocation--it is better than failure. > > */ > > scale_factor = max_t(unsigned int, 8, nn->nfsd_serv->sv_nrthreads); > > > > avail = clamp_t(unsigned long, avail, slotsize, > > total_avail/scale_factor); > > num = min_t(int, num, avail / slotsize); > > num = max_t(int, num, 1); > > > > Lets rework it a bit... > > if (nfsd_drc_max_mem > nfsd_drc_mem_used) { > > total_avail = nfsd_drc_max_mem - nfsd_drc_mem_used; > > avail = min(NFSD_MAX_MEM_PER_SESSION, total_avail); > > avail = clamp(avail, n + sizeof(xxx), total_avail/8) > > } else { > > total_avail = 0; > > avail = 0; > > avail = clamp(0, n + sizeof(xxx), 0); > > } > > > > Neither of those clamp() are sane at all - should be clamp(val, lo, hi) > > with 'lo <= hi' otherwise the result is dependant on the order of the > > comparisons. > > The compiler sees the second one and rightly bleats. > > I can't even guess what the code is actually trying to calculate! > > > > Maybe looking at where the code came from, or the current version might help. > > The current upstream code is part of a new feature that is not > appropriate to backport to LTS kernels. I consider that code out of > play. > > The compiler error showed up in 6.1.y with the recent minmax.h > changes -- there have been no reported problems in any of the LTS > kernels until now, including with 32-bit builds. > > The usual guidelines about regressions suggest that the most recent > backports (ie, minmax.h) are the ones that should be removed or reworked > to address the compile breakage. I don't think we should address this by > writing special clean-ups to code that wasn't broken before the minmax.h > changes. Cleaning that code up is more likely to introduce bugs than > reverting the minmax.h changes. No, that code needs fixing. It is broken..... The compiler warning/error is completely valid. The result of that clamp() has never been well defined. It is likely that it always generated the wrong result. It might be that a much older version of the function exists before someone changed a pair of conditionals to be a call to clamp(). That old version may well be fine. David > > > > It MIGHT be that the 'lo' of slotsize was an attempt to ensure that > > the following 'avail / slotsize' was as least one. > > Some software archaeology might show that the 'num = max(num, 1)' was added > > because the code above didn't work. > > In that case the clamp can be clamp(avail, 0, total_avail/scale_factor) > > which is just min(avail, total_avail/scale_factor). > > > > The person who rewrote it between 6.1 and 6.18 might now more. > > > > David > > > >> > >> > >> -------- Forwarded Message -------- > >> Subject: Re: Compile Error fs/nfsd/nfs4state.o - clamp() low limit > >> slotsize greater than high limit total_avail/scale_factor > >> Date: Thu, 06 Nov 2025 07:29:25 -0500 > >> From: Jeff Layton > >> To: Mike-SPC via Bugspray Bot , cel@kernel.org, > >> neilb@ownmail.net, trondmy@kernel.org, linux-nfs@vger.kernel.org, > >> anna@kernel.org, neilb@brown.name > >> > >> On Thu, 2025-11-06 at 11:30 +0000, Mike-SPC via Bugspray Bot wrote: > >>> Mike-SPC writes via Kernel.org Bugzilla: > >>> > >>> (In reply to Bugspray Bot from comment #5) > >>>> Chuck Lever replies to comment #4: > >>>> > >>>> On 11/5/25 7:25 AM, Mike-SPC via Bugspray Bot wrote: > >>>>> Mike-SPC writes via Kernel.org Bugzilla: > >>>>> > >>>>>> Have you found a 6.1.y kernel for which the build doesn't fail? > >>>>> > >>>>> Yes. Compiling Version 6.1.155 works without problems. > >>>>> Versions >= 6.1.156 aren't. > >>>> > >>>> My analysis yesterday suggests that, because the nfs4state.c code hasn't > >>>> changed, it's probably something elsewhere that introduced this problem. > >>>> As we can't reproduce the issue, can you use "git bisect" between > >>>> v6.1.155 and v6.1.156 to find the culprit commit? > >>>> > >>>> (via https://msgid.link/ab235dbe-7949-4208-a21a-2cdd50347152@kernel.org) > >>> > >>> > >>> Yes, your analysis is right (thanks for it). > >>> After some investigation, the issue appears to be caused by changes introduced in > >>> include/linux/minmax.h. > >>> > >>> I verified this by replacing minmax.h in 6.1.156 with the version from 6.1.155, > >>> and the kernel then compiles successfully. > >>> > >>> The relevant section in the 6.1.156 changelog (https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.1.156) shows several modifications to minmax.h (notably around __clamp_once() and the use of > >>> BUILD_BUG_ON_MSG(statically_true(ulo > uhi), ...)), which seem to trigger a compile-time assertion when building NFSD. > >>> > >>> Replacing the updated header with the previous one resolves the issue, so this appears > >>> to be a regression introduced by the new clamp() logic. > >>> > >>> Could you please advise who is the right person or mailing list to report this issue to > >>> (minmax.h maintainers, kernel core, or stable tree)? > >>> > >> > >> I'd let all 3 know, and I'd include the author of the patches that you > >> suspect are the problem. They'll probably want to revise the one that's > >> a problem. > >> > >> Cheers, > > > >