From patchwork Sun Dec 3 19:23:48 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yury Norov X-Patchwork-Id: 750624 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="lhpJ51on" Received: from mail-qk1-x729.google.com (mail-qk1-x729.google.com [IPv6:2607:f8b0:4864:20::729]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D142BD6; Sun, 3 Dec 2023 11:24:28 -0800 (PST) Received: by mail-qk1-x729.google.com with SMTP id af79cd13be357-77dc38b4e8dso262734285a.1; Sun, 03 Dec 2023 11:24:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1701631467; x=1702236267; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=zQMxTVPAK6MFSjY9bikHe7s4rwhQ9hzDceOswvDYFYU=; b=lhpJ51on/g7X0QySsgZ95rDDmFKGysipzZ6EWdjI7aHdFhHFN3371GRF+BScNUhg4S PjWfxml1GFpYQwq/JbvB6XWmK9VwVCScmwpE+zK/RkodRgJoA9yzLt2yuJH0LK6L2Y0A Dl2116YbqxC8ao6lJ//f8TI8fksbFP1V7QY1wTmwQD7kAQHNtEreApwfGfpWmswLmGbq 4/y1pCTiSiBZ2vnnNuQ0KnrUxBGyJQ325y3z8UaD6WLyA1eMECiRFZPZH55RgwBF3kEc vGIL3HwcthUNYT6NPpIxq+nQvzPQeVOdKS13PX8RRFKcIqwmTJw8PdIeogNmLjMyyewi SaGQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701631467; x=1702236267; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=zQMxTVPAK6MFSjY9bikHe7s4rwhQ9hzDceOswvDYFYU=; b=Iyr+I6nBQdoY5rkPPWfCOXhC/TZx+UaQpMS6dJfQM4nje8r42Mk2iLK5Xbc1isi7EF jVAASpEzSYE4eP2GJjDN4GvqSrk2qvqo1p9JI3Pcg/oduBOIjIl1nyHgFTo4aMY9UEdM ppyy6PL/bp6t+pVm06myFMN62BGdnRIp8yxIx1/DlQ9TjhdNZmHF7llzJDzXyey5shvw Lpc+lEXtTRae9vXwIMcSDStvEYJhcpMyvBBAP9/N1J/vdyh27bdPT0L/it2AZj2+Sp8k oB2AJmVpiyWhqoPCyyD4c96gBFdvbanlJROnT9eEFO+aRRvtijPQls7tYwDfcQttvdX4 AT6A== X-Gm-Message-State: AOJu0Yyb64fLqdNZi7Q9XRhQWByGmk18htGcSjDqjzITl2Ob7/r5znAS UGMhi9EKewC9hdPD/6m6jjacAljMDsdbhQ== X-Google-Smtp-Source: AGHT+IFooxiJZ8V1LpPTaQzP0LVV51jzAeTcdeLK0ZC96y8JrbBNrIJa1nUbAIA9L7CEuItTj3tUXQ== X-Received: by 2002:a05:620a:1d01:b0:77e:fba3:58bf with SMTP id dl1-20020a05620a1d0100b0077efba358bfmr4125683qkb.80.1701631466751; Sun, 03 Dec 2023 11:24:26 -0800 (PST) Received: from localhost ([2601:344:8301:57f0:cb98:c3e:57c:8191]) by smtp.gmail.com with ESMTPSA id n14-20020a819e4e000000b0059b2be24f88sm2674090ywj.143.2023.12.03.11.24.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 03 Dec 2023 11:24:26 -0800 (PST) From: Yury Norov To: linux-kernel@vger.kernel.org, "David S. Miller" , "H. Peter Anvin" , "James E.J. Bottomley" , "K. Y. Srinivasan" , "Md. Haris Iqbal" , Akinobu Mita , Andrew Morton , Bjorn Andersson , Borislav Petkov , Chaitanya Kulkarni , Christian Brauner , Damien Le Moal , Dave Hansen , David Disseldorp , Edward Cree , Eric Dumazet , Fenghua Yu , Geert Uytterhoeven , Greg Kroah-Hartman , Gregory Greenman , Hans Verkuil , Hans de Goede , Hugh Dickins , Ingo Molnar , Jakub Kicinski , Jaroslav Kysela , Jason Gunthorpe , Jens Axboe , Jiri Pirko , Jiri Slaby , Kalle Valo , Karsten Graul , Karsten Keil , Kees Cook , Leon Romanovsky , Mark Rutland , Martin Habets , Mauro Carvalho Chehab , Michael Ellerman , Michal Simek , Nicholas Piggin , Oliver Neukum , Paolo Abeni , Paolo Bonzini , Peter Zijlstra , Ping-Ke Shih , Rich Felker , Rob Herring , Robin Murphy , Sean Christopherson , Shuai Xue , Stanislaw Gruszka , Steven Rostedt , Thomas Bogendoerfer , Thomas Gleixner , Valentin Schneider , Vitaly Kuznetsov , Wenjia Zhang , Will Deacon , Yoshinori Sato , GR-QLogic-Storage-Upstream@marvell.com, alsa-devel@alsa-project.org, ath10k@lists.infradead.org, dmaengine@vger.kernel.org, iommu@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-block@vger.kernel.org, linux-bluetooth@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-media@vger.kernel.org, linux-mips@vger.kernel.org, linux-net-drivers@amd.com, linux-pci@vger.kernel.org, linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-serial@vger.kernel.org, linux-sh@vger.kernel.org, linux-sound@vger.kernel.org, linux-usb@vger.kernel.org, linux-wireless@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, mpi3mr-linuxdrv.pdl@broadcom.com, netdev@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org Cc: Yury Norov , Jan Kara , Mirsad Todorovac , Matthew Wilcox , Rasmus Villemoes , Andy Shevchenko , Maxim Kuvyrkov , Alexey Klimov , Bart Van Assche , Sergey Shtylyov Subject: [PATCH v2 01/35] lib/find: add atomic find_bit() primitives Date: Sun, 3 Dec 2023 11:23:48 -0800 Message-Id: <20231203192422.539300-2-yury.norov@gmail.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20231203192422.539300-1-yury.norov@gmail.com> References: <20231203192422.539300-1-yury.norov@gmail.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add helpers around test_and_{set,clear}_bit() that allow to search for clear or set bits and flip them atomically. The target patterns may look like this: for (idx = 0; idx < nbits; idx++) if (test_and_clear_bit(idx, bitmap)) do_something(idx); Or like this: do { bit = find_first_bit(bitmap, nbits); if (bit >= nbits) return nbits; } while (!test_and_clear_bit(bit, bitmap)); return bit; In both cases, the opencoded loop may be converted to a single function or iterator call. Correspondingly: for_each_test_and_clear_bit(idx, bitmap, nbits) do_something(idx); Or: return find_and_clear_bit(bitmap, nbits); Obviously, the less routine code people have to write themself, the less probability to make a mistake. Those are not only handy helpers but also resolve a non-trivial issue of using non-atomic find_bit() together with atomic test_and_{set,clear)_bit(). The trick is that find_bit() implies that the bitmap is a regular non-volatile piece of memory, and compiler is allowed to use such optimization techniques like re-fetching memory instead of caching it. For example, find_first_bit() is implemented like this: for (idx = 0; idx * BITS_PER_LONG < sz; idx++) { val = addr[idx]; if (val) { sz = min(idx * BITS_PER_LONG + __ffs(val), sz); break; } } On register-memory architectures, like x86, compiler may decide to access memory twice - first time to compare against 0, and second time to fetch its value to pass it to __ffs(). When running find_first_bit() on volatile memory, the memory may get changed in-between, and for instance, it may lead to passing 0 to __ffs(), which is undefined. This is a potentially dangerous call. find_and_clear_bit() as a wrapper around test_and_clear_bit() naturally treats underlying bitmap as a volatile memory and prevents compiler from such optimizations. Now that KCSAN is catching exactly this type of situations and warns on undercover memory modifications. We can use it to reveal improper usage of find_bit(), and convert it to atomic find_and_*_bit() as appropriate. The 1st patch of the series adds the following atomic primitives: find_and_set_bit(addr, nbits); find_and_set_next_bit(addr, nbits, start); ... Here find_and_{set,clear} part refers to the corresponding test_and_{set,clear}_bit function. Suffixes like _wrap or _lock derive their semantics from corresponding find() or test() functions. For brevity, the naming omits the fact that we search for zero bit in find_and_set, and correspondingly search for set bit in find_and_clear functions. The patch also adds iterators with atomic semantics, like for_each_test_and_set_bit(). Here, the naming rule is to simply prefix corresponding atomic operation with 'for_each'. All users of find_bit() API, where heavy concurrency is expected, are encouraged to switch to atomic find_and_bit() as appropriate. CC: Bart Van Assche CC: Sergey Shtylyov Signed-off-by: Yury Norov --- include/linux/find.h | 293 +++++++++++++++++++++++++++++++++++++++++++ lib/find_bit.c | 85 +++++++++++++ 2 files changed, 378 insertions(+) diff --git a/include/linux/find.h b/include/linux/find.h index 5e4f39ef2e72..79b0e2589725 100644 --- a/include/linux/find.h +++ b/include/linux/find.h @@ -32,6 +32,16 @@ extern unsigned long _find_first_and_bit(const unsigned long *addr1, extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size); extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long size); +unsigned long _find_and_set_bit(volatile unsigned long *addr, unsigned long nbits); +unsigned long _find_and_set_next_bit(volatile unsigned long *addr, unsigned long nbits, + unsigned long start); +unsigned long _find_and_set_bit_lock(volatile unsigned long *addr, unsigned long nbits); +unsigned long _find_and_set_next_bit_lock(volatile unsigned long *addr, unsigned long nbits, + unsigned long start); +unsigned long _find_and_clear_bit(volatile unsigned long *addr, unsigned long nbits); +unsigned long _find_and_clear_next_bit(volatile unsigned long *addr, unsigned long nbits, + unsigned long start); + #ifdef __BIG_ENDIAN unsigned long _find_first_zero_bit_le(const unsigned long *addr, unsigned long size); unsigned long _find_next_zero_bit_le(const unsigned long *addr, unsigned @@ -460,6 +470,267 @@ unsigned long __for_each_wrap(const unsigned long *bitmap, unsigned long size, return bit < start ? bit : size; } +/** + * find_and_set_bit - Find a zero bit and set it atomically + * @addr: The address to base the search on + * @nbits: The bitmap size in bits + * + * This function is designed to operate in concurrent access environment. + * + * Because of concurrency and volatile nature of underlying bitmap, it's not + * guaranteed that the found bit is the 1st bit in the bitmap. It's also not + * guaranteed that if @nbits is returned, the bitmap is empty. + * + * The function does guarantee that if returned value is in range [0 .. @nbits), + * the acquired bit belongs to the caller exclusively. + * + * Returns: found and set bit, or @nbits if no bits found + */ +static inline +unsigned long find_and_set_bit(volatile unsigned long *addr, unsigned long nbits) +{ + if (small_const_nbits(nbits)) { + unsigned long val, ret; + + do { + val = *addr | ~GENMASK(nbits - 1, 0); + if (val == ~0UL) + return nbits; + ret = ffz(val); + } while (test_and_set_bit(ret, addr)); + + return ret; + } + + return _find_and_set_bit(addr, nbits); +} + + +/** + * find_and_set_next_bit - Find a zero bit and set it, starting from @offset + * @addr: The address to base the search on + * @nbits: The bitmap nbits in bits + * @offset: The bitnumber to start searching at + * + * This function is designed to operate in concurrent access environment. + * + * Because of concurrency and volatile nature of underlying bitmap, it's not + * guaranteed that the found bit is the 1st bit in the bitmap, starting from @offset. + * It's also not guaranteed that if @nbits is returned, the bitmap is empty. + * + * The function does guarantee that if returned value is in range [@offset .. @nbits), + * the acquired bit belongs to the caller exclusively. + * + * Returns: found and set bit, or @nbits if no bits found + */ +static inline +unsigned long find_and_set_next_bit(volatile unsigned long *addr, + unsigned long nbits, unsigned long offset) +{ + if (small_const_nbits(nbits)) { + unsigned long val, ret; + + do { + val = *addr | ~GENMASK(nbits - 1, offset); + if (val == ~0UL) + return nbits; + ret = ffz(val); + } while (test_and_set_bit(ret, addr)); + + return ret; + } + + return _find_and_set_next_bit(addr, nbits, offset); +} + +/** + * find_and_set_bit_wrap - find and set bit starting at @offset, wrapping around zero + * @addr: The first address to base the search on + * @nbits: The bitmap size in bits + * @offset: The bitnumber to start searching at + * + * Returns: the bit number for the next clear bit, or first clear bit up to @offset, + * while atomically setting it. If no bits are found, returns @nbits. + */ +static inline +unsigned long find_and_set_bit_wrap(volatile unsigned long *addr, + unsigned long nbits, unsigned long offset) +{ + unsigned long bit = find_and_set_next_bit(addr, nbits, offset); + + if (bit < nbits || offset == 0) + return bit; + + bit = find_and_set_bit(addr, offset); + return bit < offset ? bit : nbits; +} + +/** + * find_and_set_bit_lock - find a zero bit, then set it atomically with lock + * @addr: The address to base the search on + * @nbits: The bitmap nbits in bits + * + * This function is designed to operate in concurrent access environment. + * + * Because of concurrency and volatile nature of underlying bitmap, it's not + * guaranteed that the found bit is the 1st bit in the bitmap. It's also not + * guaranteed that if @nbits is returned, the bitmap is empty. + * + * The function does guarantee that if returned value is in range [0 .. @nbits), + * the acquired bit belongs to the caller exclusively. + * + * Returns: found and set bit, or @nbits if no bits found + */ +static inline +unsigned long find_and_set_bit_lock(volatile unsigned long *addr, unsigned long nbits) +{ + if (small_const_nbits(nbits)) { + unsigned long val, ret; + + do { + val = *addr | ~GENMASK(nbits - 1, 0); + if (val == ~0UL) + return nbits; + ret = ffz(val); + } while (test_and_set_bit_lock(ret, addr)); + + return ret; + } + + return _find_and_set_bit_lock(addr, nbits); +} + +/** + * find_and_set_next_bit_lock - find a zero bit and set it atomically with lock + * @addr: The address to base the search on + * @nbits: The bitmap size in bits + * @offset: The bitnumber to start searching at + * + * This function is designed to operate in concurrent access environment. + * + * Because of concurrency and volatile nature of underlying bitmap, it's not + * guaranteed that the found bit is the 1st bit in the range. It's also not + * guaranteed that if @nbits is returned, the bitmap is empty. + * + * The function does guarantee that if returned value is in range [@offset .. @nbits), + * the acquired bit belongs to the caller exclusively. + * + * Returns: found and set bit, or @nbits if no bits found + */ +static inline +unsigned long find_and_set_next_bit_lock(volatile unsigned long *addr, + unsigned long nbits, unsigned long offset) +{ + if (small_const_nbits(nbits)) { + unsigned long val, ret; + + do { + val = *addr | ~GENMASK(nbits - 1, offset); + if (val == ~0UL) + return nbits; + ret = ffz(val); + } while (test_and_set_bit_lock(ret, addr)); + + return ret; + } + + return _find_and_set_next_bit_lock(addr, nbits, offset); +} + +/** + * find_and_set_bit_wrap_lock - find zero bit starting at @ofset and set it + * with lock, and wrap around zero if nothing found + * @addr: The first address to base the search on + * @nbits: The bitmap size in bits + * @offset: The bitnumber to start searching at + * + * Returns: the bit number for the next set bit, or first set bit up to @offset + * If no bits are set, returns @nbits. + */ +static inline +unsigned long find_and_set_bit_wrap_lock(volatile unsigned long *addr, + unsigned long nbits, unsigned long offset) +{ + unsigned long bit = find_and_set_next_bit_lock(addr, nbits, offset); + + if (bit < nbits || offset == 0) + return bit; + + bit = find_and_set_bit_lock(addr, offset); + return bit < offset ? bit : nbits; +} + +/** + * find_and_clear_bit - Find a set bit and clear it atomically + * @addr: The address to base the search on + * @nbits: The bitmap nbits in bits + * + * This function is designed to operate in concurrent access environment. + * + * Because of concurrency and volatile nature of underlying bitmap, it's not + * guaranteed that the found bit is the 1st bit in the bitmap. It's also not + * guaranteed that if @nbits is returned, the bitmap is empty. + * + * The function does guarantee that if returned value is in range [0 .. @nbits), + * the acquired bit belongs to the caller exclusively. + * + * Returns: found and cleared bit, or @nbits if no bits found + */ +static inline unsigned long find_and_clear_bit(volatile unsigned long *addr, unsigned long nbits) +{ + if (small_const_nbits(nbits)) { + unsigned long val, ret; + + do { + val = *addr & GENMASK(nbits - 1, 0); + if (val == 0) + return nbits; + ret = __ffs(val); + } while (!test_and_clear_bit(ret, addr)); + + return ret; + } + + return _find_and_clear_bit(addr, nbits); +} + +/** + * find_and_clear_next_bit - Find a set bit next after @offset, and clear it atomically + * @addr: The address to base the search on + * @nbits: The bitmap nbits in bits + * @offset: bit offset at which to start searching + * + * This function is designed to operate in concurrent access environment. + * + * Because of concurrency and volatile nature of underlying bitmap, it's not + * guaranteed that the found bit is the 1st bit in the range It's also not + * guaranteed that if @nbits is returned, there's no set bits after @offset. + * + * The function does guarantee that if returned value is in range [@offset .. @nbits), + * the acquired bit belongs to the caller exclusively. + * + * Returns: found and cleared bit, or @nbits if no bits found + */ +static inline +unsigned long find_and_clear_next_bit(volatile unsigned long *addr, + unsigned long nbits, unsigned long offset) +{ + if (small_const_nbits(nbits)) { + unsigned long val, ret; + + do { + val = *addr & GENMASK(nbits - 1, offset); + if (val == 0) + return nbits; + ret = __ffs(val); + } while (!test_and_clear_bit(ret, addr)); + + return ret; + } + + return _find_and_clear_next_bit(addr, nbits, offset); +} + /** * find_next_clump8 - find next 8-bit clump with set bits in a memory region * @clump: location to store copy of found clump @@ -577,6 +848,28 @@ unsigned long find_next_bit_le(const void *addr, unsigned #define for_each_set_bit_from(bit, addr, size) \ for (; (bit) = find_next_bit((addr), (size), (bit)), (bit) < (size); (bit)++) +/* same as for_each_set_bit() but atomically clears each found bit */ +#define for_each_test_and_clear_bit(bit, addr, size) \ + for ((bit) = 0; \ + (bit) = find_and_clear_next_bit((addr), (size), (bit)), (bit) < (size); \ + (bit)++) + +/* same as for_each_set_bit_from() but atomically clears each found bit */ +#define for_each_test_and_clear_bit_from(bit, addr, size) \ + for (; (bit) = find_and_clear_next_bit((addr), (size), (bit)), (bit) < (size); (bit)++) + +/* same as for_each_clear_bit() but atomically sets each found bit */ +#define for_each_test_and_set_bit(bit, addr, size) \ + for ((bit) = 0; \ + (bit) = find_and_set_next_bit((addr), (size), (bit)), (bit) < (size); \ + (bit)++) + +/* same as for_each_clear_bit_from() but atomically clears each found bit */ +#define for_each_test_and_set_bit_from(bit, addr, size) \ + for (; \ + (bit) = find_and_set_next_bit((addr), (size), (bit)), (bit) < (size); \ + (bit)++) + #define for_each_clear_bit(bit, addr, size) \ for ((bit) = 0; \ (bit) = find_next_zero_bit((addr), (size), (bit)), (bit) < (size); \ diff --git a/lib/find_bit.c b/lib/find_bit.c index 32f99e9a670e..c9b6b9f96610 100644 --- a/lib/find_bit.c +++ b/lib/find_bit.c @@ -116,6 +116,91 @@ unsigned long _find_first_and_bit(const unsigned long *addr1, EXPORT_SYMBOL(_find_first_and_bit); #endif +unsigned long _find_and_set_bit(volatile unsigned long *addr, unsigned long nbits) +{ + unsigned long bit; + + do { + bit = FIND_FIRST_BIT(~addr[idx], /* nop */, nbits); + if (bit >= nbits) + return nbits; + } while (test_and_set_bit(bit, addr)); + + return bit; +} +EXPORT_SYMBOL(_find_and_set_bit); + +unsigned long _find_and_set_next_bit(volatile unsigned long *addr, + unsigned long nbits, unsigned long start) +{ + unsigned long bit; + + do { + bit = FIND_NEXT_BIT(~addr[idx], /* nop */, nbits, start); + if (bit >= nbits) + return nbits; + } while (test_and_set_bit(bit, addr)); + + return bit; +} +EXPORT_SYMBOL(_find_and_set_next_bit); + +unsigned long _find_and_set_bit_lock(volatile unsigned long *addr, unsigned long nbits) +{ + unsigned long bit; + + do { + bit = FIND_FIRST_BIT(~addr[idx], /* nop */, nbits); + if (bit >= nbits) + return nbits; + } while (test_and_set_bit_lock(bit, addr)); + + return bit; +} +EXPORT_SYMBOL(_find_and_set_bit_lock); + +unsigned long _find_and_set_next_bit_lock(volatile unsigned long *addr, + unsigned long nbits, unsigned long start) +{ + unsigned long bit; + + do { + bit = FIND_NEXT_BIT(~addr[idx], /* nop */, nbits, start); + if (bit >= nbits) + return nbits; + } while (test_and_set_bit_lock(bit, addr)); + + return bit; +} +EXPORT_SYMBOL(_find_and_set_next_bit_lock); + +unsigned long _find_and_clear_bit(volatile unsigned long *addr, unsigned long nbits) +{ + unsigned long bit; + + do { + bit = FIND_FIRST_BIT(addr[idx], /* nop */, nbits); + if (bit >= nbits) + return nbits; + } while (!test_and_clear_bit(bit, addr)); + + return bit; +} +EXPORT_SYMBOL(_find_and_clear_bit); + +unsigned long _find_and_clear_next_bit(volatile unsigned long *addr, + unsigned long nbits, unsigned long start) +{ + do { + start = FIND_NEXT_BIT(addr[idx], /* nop */, nbits, start); + if (start >= nbits) + return nbits; + } while (!test_and_clear_bit(start, addr)); + + return start; +} +EXPORT_SYMBOL(_find_and_clear_next_bit); + #ifndef find_first_zero_bit /* * Find the first cleared bit in a memory region.