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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49092654e10sm56452765e9.7.2026.05.28.14.05.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2026 14:05:06 -0700 (PDT) Date: Thu, 28 May 2026 22:05:05 +0100 From: David Laight To: Rosen Penev Cc: linux-block@vger.kernel.org, Ilya Dryomov , Dongsheng Yang , Jens Axboe , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , ceph-devel@vger.kernel.org (open list:RADOS BLOCK DEVICE (RBD)), linux-kernel@vger.kernel.org (open list), llvm@lists.linux.dev (open list:CLANG/LLVM BUILD SUPPORT:Keyword:\b(?i:clang|llvm)\b) Subject: Re: [PATCH] rbd: cast snap_count to size_t to avoid tautological comparison warning Message-ID: <20260528220505.73eac71a@pumpkin> In-Reply-To: <20260528202151.136274-1-rosenp@gmail.com> References: <20260528202151.136274-1-rosenp@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-block@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, 28 May 2026 13:21:51 -0700 Rosen Penev wrote: > snap_count is u32 but the comparison is against a SIZE_MAX-derived value > (~2^61 on 64-bit), which clang flags as always false with > -Wtautological-constant-out-of-range-compare. Cast to size_t so the > comparison is done in the correct width. If that warning makes any sense then the cast shouldn't make any difference. Why not check against RBD_MAX_SNAP_COUNT - the buffer isn't big enough to hold any more than that. -- David > > Assisted-by: Opencode:Big-pickle > Signed-off-by: Rosen Penev > --- > drivers/block/rbd.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c > index 94709466ad19..b4ba51db9a28 100644 > --- a/drivers/block/rbd.c > +++ b/drivers/block/rbd.c > @@ -6079,7 +6079,7 @@ static int rbd_dev_v2_snap_context(struct rbd_device *rbd_dev, > * make sure the computed size of the snapshot context we > * allocate is representable in a size_t. > */ > - if (snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context)) > + if ((size_t)snap_count > (SIZE_MAX - sizeof (struct ceph_snap_context)) > / sizeof (u64)) { > ret = -EINVAL; > goto out;