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=-11.3 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 C6227C352A3 for ; Thu, 13 Feb 2020 19:21:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A078A2073A for ; Thu, 13 Feb 2020 19:21:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="pS/rA/XQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728582AbgBMTVu (ORCPT ); Thu, 13 Feb 2020 14:21:50 -0500 Received: from mail-io1-f66.google.com ([209.85.166.66]:38097 "EHLO mail-io1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727076AbgBMTVt (ORCPT ); Thu, 13 Feb 2020 14:21:49 -0500 Received: by mail-io1-f66.google.com with SMTP id s24so7780672iog.5 for ; Thu, 13 Feb 2020 11:21:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=/QOUSXFhncnCv9tdGLgXn7t709p+c+vsJCaqhbGCgQg=; b=pS/rA/XQrsxzALgzkkxUeROv/A+yx7tTwuLt9niMsfB6HwrxJMIlP3S2/4cJAI9Xxl FEwPSATlEOu0eg2zmBQmE+QLH8NFhPJGMSP43gExdI76wnbvkqAkqVwfXFs/8+X4+ZMP j9OHRJjNJPJf6srEwtDgNRoYZ2sM5AlxJ9JauV7+SkprHS0iAq04hzVRoYEkME95AMaA KWBQrY3h2AZsrbxjz6W33oBVnW+96Q/3aKr5x/uyP6f08CkG52DwaC/wKWy8OelXOhHG enBS8ih7VJX0/gHzC7y/6ktnVbeRNBA9p+kQy0prGSEVEFxHEx/6PeJiN5Xz0VnbYNg5 CaSQ== 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=/QOUSXFhncnCv9tdGLgXn7t709p+c+vsJCaqhbGCgQg=; b=K/i9zrlo4qdX7J3smlBPn2E6I8EjqfL4aApjHxRk1ENjL7MW0NSD7WPhvNaTdAbEy2 asOchqK76Ykt+RG1s0ItH3YgRFFbrzovtq3I/CdH99Z7whGJlPxs6veECsK82chxcE4r H6keLGFGRsAmNdufrvogNs4X6cxvP2pCQ8IkSzgSyT4Tn4k0smwm79HsEx7AhCIAZgMO 6lxBUAyCFqWxagWyae/dwsnmWxEMSnd78Tx0oFHSkv5fAq+9amp0dtqcqcRYkDeVr1S+ pt1UE2EJ+fgpvUL6B2VJr+LtKsxaU/Q8jnyICfb6PaQOyuZGWVUjaeMmF44r2zOwSm1E cf3w== X-Gm-Message-State: APjAAAXuUSK/5pCCnol3GPFlsA9d3u6M+SH4dsNq+Qt+WtG7dKRXzJEo AKeTHyFekkMXSCAF7G8iDXeDwp2hBE2LnGVX392HrQ== X-Google-Smtp-Source: APXvYqwbrJIHiF6yo1n6cPB8dSDhRLQlDy6lDN6DDMGk6NwCczSxpnrZielmwNpETh3CvySMVqQQMDSUdbfC5OaU1zc= X-Received: by 2002:a5d:8c84:: with SMTP id g4mr23458168ion.289.1581621708984; Thu, 13 Feb 2020 11:21:48 -0800 (PST) MIME-Version: 1.0 References: <20200213082643.GB9144@ming.t460p> In-Reply-To: From: Salman Qazi Date: Thu, 13 Feb 2020 11:21:37 -0800 Message-ID: Subject: Re: BLKSECDISCARD ioctl and hung tasks To: Bart Van Assche Cc: Ming Lei , Jens Axboe , Christoph Hellwig , Linux Kernel Mailing List , linux-block@vger.kernel.org, Gwendal Grignou , Jesse Barnes Content-Type: text/plain; charset="UTF-8" Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Feb 13, 2020 at 9:48 AM Bart Van Assche wrote: > > On 2/13/20 12:26 AM, Ming Lei wrote: > > The approach used in blk_execute_rq() can be borrowed for workaround the > > issue, such as: > > > > diff --git a/block/bio.c b/block/bio.c > > index 94d697217887..c9ce19a86de7 100644 > > --- a/block/bio.c > > +++ b/block/bio.c > > @@ -17,6 +17,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include "blk.h" > > @@ -1019,12 +1020,19 @@ static void submit_bio_wait_endio(struct bio *bio) > > int submit_bio_wait(struct bio *bio) > > { > > DECLARE_COMPLETION_ONSTACK_MAP(done, bio->bi_disk->lockdep_map); > > + unsigned long hang_check; > > > > bio->bi_private = &done; > > bio->bi_end_io = submit_bio_wait_endio; > > bio->bi_opf |= REQ_SYNC; > > submit_bio(bio); > > - wait_for_completion_io(&done); > > + > > + /* Prevent hang_check timer from firing at us during very long I/O */ > > + hang_check = sysctl_hung_task_timeout_secs; > > + if (hang_check) > > + while (!wait_for_completion_io_timeout(&done, hang_check * (HZ/2))); > > + else > > + wait_for_completion_io(&done); > > > > return blk_status_to_errno(bio->bi_status); > > } > > Instead of suppressing the hung task complaints, has it been considered > to use the bio splitting mechanism to make discard bios smaller? Block > drivers may set a limit by calling blk_queue_max_discard_segments(). > From block/blk-settings.c: > > /** > * blk_queue_max_discard_segments - set max segments for discard > * requests > * @q: the request queue for the device > * @max_segments: max number of segments > * > * Description: > * Enables a low level driver to set an upper limit on the number of > * segments in a discard request. > **/ > void blk_queue_max_discard_segments(struct request_queue *q, > unsigned short max_segments) > { > q->limits.max_discard_segments = max_segments; > } > EXPORT_SYMBOL_GPL(blk_queue_max_discard_segments); > AFAICT, This is not actually sufficient, because the issuer of the bio is waiting for the entire bio, regardless of how it is split later. But, also there isn't a good mapping between the size of the secure discard and how long it will take. If given the geometry of a flash device, it is not hard to construct a scenario where a relatively small secure discard (few thousand sectors) will take a very long time (multiple seconds). Having said that, I don't like neutering the hung task timer either. > Thanks, > > Bart.