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=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 565DFC19425 for ; Sat, 12 Dec 2020 10:02:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 27A9020684 for ; Sat, 12 Dec 2020 10:02:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2438469AbgLLJ6r (ORCPT ); Sat, 12 Dec 2020 04:58:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42438 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388329AbgLLJ6o (ORCPT ); Sat, 12 Dec 2020 04:58:44 -0500 Received: from mail-io1-xd44.google.com (mail-io1-xd44.google.com [IPv6:2607:f8b0:4864:20::d44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDC57C0613CF; Sat, 12 Dec 2020 01:58:03 -0800 (PST) Received: by mail-io1-xd44.google.com with SMTP id z5so12072161iob.11; Sat, 12 Dec 2020 01:58:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=VfC8U3+9RgAipJV6RtcOXOTncWoLx+pvsz+FVUtT+WM=; b=ru8KqwZkrp8biP002XsKcZ7D9aatn+KC/DegPBreXXE6ZS1KMc/Z2M2WmwW/rQAwED ySiXaA+fHXKjtOEjXJFmS2KxBd+ec+Y70LX4Pk7z9M8MhCoAVz4j/WRJOSNINxfivoGy GDqSbNVGtCAdz19ntqGL4YhucICczEsvnsIK1IohMq8G/GJvv7igdgtJbHYr5c2VYy50 OVHwhsUVdRTzwCd+58mvjJX/NG+vDKlZIGZkYZRHzLMx6CAQnUEtILIwzXg1Uq3RjVYE qDu5NyFAlIQqGmdLaQeJVLB+LvzOD2Jaeq5oZt8QOdSM+BuYHHZiYGISF9bV2y0Udiqd iKtA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=VfC8U3+9RgAipJV6RtcOXOTncWoLx+pvsz+FVUtT+WM=; b=B+j3aapKDBcQwzc9Au/qebRV0Q+pO36JCQfq9iMz/+OAs5FTQFwpI1RQTCz7ZZmT3V i759zfNoPOs4d1WBG1pkP2lsRbel+NORW37uDkyNDrKu+wE6qPvtpqU5/tt0PiYro39S s/OTgMDBMOyDT1Z4x8bJpX16Z7pxYNqv67PJLuPjijQls1FBbhVrwQVFa6Mjycqqr+E0 jVl56+AvQuoEUk7o63/htXDvE7g7NhdaptFnoHVguofJTFtLLN9wyONcgc2ATGc0/pH7 aqDKPXDkl2sv64Q91P4S7rY48uocnNnyW5qZ8HOcWpgvNqdznucZHndDc4oCD7t3pAGZ vF4g== X-Gm-Message-State: AOAM533T2u9A/ir2n+U6DrAmFOpAN6leUROQyzXEwE7OH7vj04Ip1C92 BuwKm2w5gbPdHtJQzJlqvT0JCqGLcoDjbg4XCQI= X-Google-Smtp-Source: ABdhPJzmJSTtlvPRlby9CqpfmwXRf7R6w5YTMgILXhIqKEo4qqH4jQyqzvvTqqn3shcnX3rL3DHEDwbVItsF8VIsmMw= X-Received: by 2002:a02:b607:: with SMTP id h7mr21485997jam.120.1607767083180; Sat, 12 Dec 2020 01:58:03 -0800 (PST) MIME-Version: 1.0 References: <20201211235002.4195-1-sargun@sargun.me> <20201211235002.4195-3-sargun@sargun.me> In-Reply-To: <20201211235002.4195-3-sargun@sargun.me> From: Amir Goldstein Date: Sat, 12 Dec 2020 11:57:52 +0200 Message-ID: Subject: Re: [PATCH v2 2/3] errseq: Add mechanism to snapshot errseq_counter and check snapshot To: Sargun Dhillon Cc: Miklos Szeredi , Vivek Goyal , overlayfs , Linux FS-devel Mailing List , Matthew Wilcox , Jeff Layton Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org Forgot to CC Jeff? On Sat, Dec 12, 2020 at 1:50 AM Sargun Dhillon wrote: > > This adds the function errseq_counter_sample to allow for "subscribers" > to take point-in-time snapshots of the errseq_counter, and store the > counter + errseq_t. > > Signed-off-by: Sargun Dhillon > --- > include/linux/errseq.h | 4 ++++ > lib/errseq.c | 51 ++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 55 insertions(+) > > diff --git a/include/linux/errseq.h b/include/linux/errseq.h > index 35818c484290..8998df499a3b 100644 > --- a/include/linux/errseq.h > +++ b/include/linux/errseq.h > @@ -25,4 +25,8 @@ errseq_t errseq_set(errseq_t *eseq, int err); > errseq_t errseq_sample(errseq_t *eseq); > int errseq_check(errseq_t *eseq, errseq_t since); > int errseq_check_and_advance(errseq_t *eseq, errseq_t *since); > +void errseq_counter_sample(errseq_t *dst_errseq, int *dst_errors, > + struct errseq_counter *counter); > +int errseq_counter_check(struct errseq_counter *counter, errseq_t errseq_since, > + int errors_since); > #endif > diff --git a/lib/errseq.c b/lib/errseq.c > index d555e7fc18d2..98fcfafa3d97 100644 > --- a/lib/errseq.c > +++ b/lib/errseq.c > @@ -246,3 +246,54 @@ int errseq_check_and_advance(errseq_t *eseq, errseq_t *since) > return err; > } > EXPORT_SYMBOL(errseq_check_and_advance); > + > +/** > + * errseq_counter_sample() - Grab the current errseq_counter value > + * @dst_errseq: The errseq_t to copy to > + * @dst_errors: The destination overflow to copy to > + * @counter: The errseq_counter to copy from > + * > + * Grabs a point in time sample of the errseq_counter for latter comparison > + */ > +void errseq_counter_sample(errseq_t *dst_errseq, int *dst_errors, Why 2 arguments and not struct errseq_counter *dst_counter? > + struct errseq_counter *counter) > +{ > + errseq_t cur; > + > + do { > + cur = READ_ONCE(counter->errseq); > + *dst_errors = atomic_read(&counter->errors); > + } while (cur != READ_ONCE(counter->errseq)); This loop seems odd. I think the return value should reflect the fact that the snapshot failed and let the caller decide if it wants to loop. And about the one and only introduced caller, I think the answer is that it shouldn't loop. If volatile overlayfs mount tries to sample the upper sb error counter and an unseen error exists, I argued before that I think mount should fail, so that the container orchestrator can decide what to do. Failure to take an errseq_counter sample means than an unseen error has been observed at least in the first or second check. > + > + /* Clear the seen bit to make checking later easier */ > + *dst_errseq = cur & ~ERRSEQ_SEEN; > +} > +EXPORT_SYMBOL(errseq_counter_sample); > + > +/** > + * errseq_counter_check() - Has an error occurred since the sample > + * @counter: The errseq_counter from which to check. > + * @errseq_since: The errseq_t sampled with errseq_counter_sample to check > + * @errors_since: The errors sampled with errseq_counter_sample to check > + * > + * Returns: The latest error set in the errseq_t or 0 if there have been none. > + */ > +int errseq_counter_check(struct errseq_counter *counter, errseq_t errseq_since, > + int errors_since) > +{ > + errseq_t cur_errseq; > + int cur_errors; > + > + cur_errors = atomic_read(&counter->errors); > + /* To match the barrier in errseq_counter_set */ > + smp_rmb(); > + > + /* Clear / ignore the seen bit as we do at sample time */ > + cur_errseq = READ_ONCE(counter->errseq) & ~ERRSEQ_SEEN; > + > + if (cur_errseq == errseq_since && errors_since == cur_errors) > + return 0; > + > + return -(cur_errseq & MAX_ERRNO); > +} Same here. Why not pass an errseq_counter_since argument? Thanks, Amir.