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Wed, 04 Nov 2026 13:51:54 -0800 (PST) Received: from localhost ([2a00:79e0:2ebe:8:c8f4:b7d9:252f:4483]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b245c1c127sm10459946c88.6.2026.11.04.13.51.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 13:51:53 -0800 (PST) Date: Wed, 04 Nov 2026 13:51:52 -0800 Message-ID: <73caedd26b375ae7671d24bcee115f05@gmail.com> From: Dmitry Torokhov To: Andy Shevchenko Cc: Linus Walleij , Bartosz Golaszewski , Andy Shevchenko , Janusz Krzysztofik , linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 6/7] gpiolib: avoid krealloc() in gpiod_get_array() In-Reply-To: References: <20261103-b4-gpiolib-free-v2-0-ea46767c9cf8@gmail.com> <20261103-b4-gpiolib-free-v2-6-ea46767c9cf8@gmail.com> <4e7b28ae9ad5de3708c549d62a4bae68@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline On Wed, Nov 04, 2026 at 11:40:18PM +0200, Andy Shevchenko wrote: > On Wed, Nov 04, 2026 at 10:14:49AM -0800, Dmitry Torokhov wrote: > > On Wed, Nov 04, 2026 at 02:20:53PM +0200, Andy Shevchenko wrote: > > > On Tue, Nov 03, 2026 at 07:40:34PM -0800, Dmitry Torokhov wrote: > > > > + bitmap_set(array_info->get_mask, 0, count); > > > > + bitmap_set(array_info->set_mask, 0, count); > > > > > > You don't need these, as memory is nullified. > > > Also note that we have bitmap_clear() IIRC. > > > > bitmap_set() sets bits 0 .. count - 1 to 1, not 0. Both get_mask and > > set_mask start with all count bits set (assuming all pins in the array > > are eligible for the fast path), and then gpio_descs_check_fastpath() > > clears individual bits for pins that do not qualify. > > Ah, indeed, but we still have bitmap_fill(). bitmap_fill(dst, count) fills whole unsigned long words with 0xff without masking the tail bits in the last word. Here get_mask and set_mask are sized to max(gdev->ngpio, count) bits and passed to gpio_chip_get_multiple() and gpiochip_set_multiple(), which iterate up to gc->ngpio bits. When count < gdev->ngpio, bitmap_fill(mask, count) would leave bits count .. round_up(count, BITS_PER_LONG) - 1 set to 1, causing get_multiple/set_multiple to touch unrelated pins on the chip and access value_bitmap beyond count bits. So we really need bitmap_set(..., 0, count) here to set only the first count bits. Thanks. -- Dmitry