From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 84F62C47082 for ; Tue, 8 Jun 2021 12:35:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6CDCB61287 for ; Tue, 8 Jun 2021 12:35:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232635AbhFHMhm (ORCPT ); Tue, 8 Jun 2021 08:37:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34440 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232579AbhFHMhl (ORCPT ); Tue, 8 Jun 2021 08:37:41 -0400 Received: from mail-pf1-x42b.google.com (mail-pf1-x42b.google.com [IPv6:2607:f8b0:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E78BC061574 for ; Tue, 8 Jun 2021 05:35:49 -0700 (PDT) Received: by mail-pf1-x42b.google.com with SMTP id g6so15603833pfq.1 for ; Tue, 08 Jun 2021 05:35:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to:cc; bh=EtSen5x9pYOvSCLuPlXvWs/V8hs2GAQuKNJwTnNHRe0=; b=jnGctsQSD2ll882C3rvRdrk9ZcBMqRBFH82PxAi60Fr8cIvux379jQyLL5VZLnLlRU IzQB8d0p9N8/LgZEirr3KJcfl1AnSH+/KpCThC+HMKJ+0cPnkEKVF6eDSa8Sx5Hhy4IQ VmFuBIqRJYu6hGUM34Kpxi2hOWe3sv3DFb31FCAqhdHaHDUyDkc4CEXaKVXbXxh0X81N v5Ysso+LRBwwsEkl37Kfiag2oOM1rW220lLAjQfEw1L2hPAFRMnNpJDXX4UYl7kSvRzj mJ+EITs4uTy/zPXhrH8bdYYkeFMU0R+1PqjH2BsVZGZ+OX251qxl6VsuQAsUcEuvBEt5 Yy6g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to:cc; bh=EtSen5x9pYOvSCLuPlXvWs/V8hs2GAQuKNJwTnNHRe0=; b=SELXybsYJ9zm+1G2bjeS1PEFLONm3lwhP8sf51BLSeTlTsQ3vLGQ1x9J3lpcAv+IR1 qpBJkS88kkVbhF7vsdC5iFWelXtB4qV2/qkxFlQmBM4L/vt0LNbRO3UJ3jw8eZljhgIa 5qH6Wwobx8y8uEZ4Ry+dwd09p5j3EBMHMMFH2uVN3rEhnne9aVmIId6Chi0Czf+CAIci XBt57Zrt3TdJqiN8GIlyn2BV8x5KBJbdgh9rY5HWx2ORUo/xsqN1kH4Jg9fv7VyHJbLz liDce098wAk+n9+u0KtKADEjF2j6OYv5h71wnSKFXIw7LXmL/EdF2h/izVl4JVU9ZyIb IOnw== X-Gm-Message-State: AOAM533SAk1nwiow2kT1WPg4mKDC/uqGKlbC+Y6+TFTqM6pGktvoDc4l 6FuE18/JyBopuhCUXZiC/NtHSxlWceWAY92yCoMvp5+8UvmPgA== X-Google-Smtp-Source: ABdhPJxpuIEgGXgd3YfKUFCEX68z4M5Nbb5w2S+zWBlCZFjDbwtqzrZKwr9chpuEgVoqS2KtmbGMFwWfMhJhftBCSZA= X-Received: by 2002:a63:b507:: with SMTP id y7mr22576075pge.74.1623155748420; Tue, 08 Jun 2021 05:35:48 -0700 (PDT) MIME-Version: 1.0 From: Andy Shevchenko Date: Tue, 8 Jun 2021 15:35:32 +0300 Message-ID: Subject: atomic use is not atomic? To: linux-iio Cc: Jonathan Cameron , Lars-Peter Clausen , Peter Meerwald Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org Hi! Can anybody explain this code [1] in terms of atomicity? if (!atomic_read(&trig->use_count)) { atomic_set(&trig->use_count, CONFIG_IIO_CONSUMERS_PER_TRIGGER); ... } AFAIU how atomics are supposed to work the above doesn't do anything atomically. I.o.w. use_count may be simple int with the same effect. What did I miss? [1]: https://elixir.bootlin.com/linux/latest/source/drivers/iio/industrialio-trigger.c#L166 -- With Best Regards, Andy Shevchenko