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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42abe64fd90sm4714454f8f.21.2025.11.07.03.43.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Nov 2025 03:43:26 -0800 (PST) Date: Fri, 7 Nov 2025 11:43:24 +0000 From: David Laight To: NeilBrown Cc: NeilBrown , "Chuck Lever" , "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: <20251107114324.33fd69f3@pumpkin> In-Reply-To: <176251424056.634289.13464296772500147856@noble.neil.brown.name> References: <37bc1037-37d8-4168-afc9-da8e2d1dd26b@kernel.org> <20251106192210.1b6a3ca0@pumpkin> <176251424056.634289.13464296772500147856@noble.neil.brown.name> 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 Fri, 07 Nov 2025 22:17:20 +1100 NeilBrown wrote: > On Fri, 07 Nov 2025, 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. > > In fact only gcc-9 bleats. That is probably why it didn't get picked up earlier. > gcc-7 gcc-10 gcc-13 gcc-15 > all seem to think it is fine. Which, of course, it isn't... David > > NeilBrown