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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 43886C43441 for ; Thu, 22 Nov 2018 09:42:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 05988206B2 for ; Thu, 22 Nov 2018 09:42:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 05988206B2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389978AbeKVUVO (ORCPT ); Thu, 22 Nov 2018 15:21:14 -0500 Received: from mx2.suse.de ([195.135.220.15]:44880 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2389946AbeKVUVO (ORCPT ); Thu, 22 Nov 2018 15:21:14 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 64CA8AE7A; Thu, 22 Nov 2018 09:42:29 +0000 (UTC) Subject: Re: [PATCH 1/6] btrfs: add btrfs_delete_ref_head helper From: Nikolay Borisov To: Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com Cc: Josef Bacik References: <20181121185912.24288-1-josef@toxicpanda.com> <20181121185912.24288-2-josef@toxicpanda.com> <9e2495bc-4bcc-046c-2416-415a7e48c681@suse.com> Openpgp: preference=signencrypt Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: <3eb452b8-d07f-530e-a16e-8d8fd5938b87@suse.com> Date: Thu, 22 Nov 2018 11:42:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <9e2495bc-4bcc-046c-2416-415a7e48c681@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 22.11.18 г. 11:12 ч., Nikolay Borisov wrote: > > > On 21.11.18 г. 20:59 ч., Josef Bacik wrote: >> From: Josef Bacik >> >> We do this dance in cleanup_ref_head and check_ref_cleanup, unify it >> into a helper and cleanup the calling functions. >> >> Signed-off-by: Josef Bacik >> Reviewed-by: Omar Sandoval >> --- >> fs/btrfs/delayed-ref.c | 14 ++++++++++++++ >> fs/btrfs/delayed-ref.h | 3 ++- >> fs/btrfs/extent-tree.c | 22 +++------------------- >> 3 files changed, 19 insertions(+), 20 deletions(-) >> >> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c >> index 9301b3ad9217..b3e4c9fcb664 100644 >> --- a/fs/btrfs/delayed-ref.c >> +++ b/fs/btrfs/delayed-ref.c >> @@ -400,6 +400,20 @@ struct btrfs_delayed_ref_head *btrfs_select_ref_head( >> return head; >> } >> >> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs, >> + struct btrfs_delayed_ref_head *head) >> +{ >> + lockdep_assert_held(&delayed_refs->lock); >> + lockdep_assert_held(&head->lock); >> + >> + rb_erase_cached(&head->href_node, &delayed_refs->href_root); >> + RB_CLEAR_NODE(&head->href_node); >> + atomic_dec(&delayed_refs->num_entries); >> + delayed_refs->num_heads--; >> + if (head->processing == 0) >> + delayed_refs->num_heads_ready--; > > num_heads_ready will never execute in cleanup_ref_head, since > processing == 0 only when the ref head is unselected. Perhaps those 2 > lines shouldn't be in this function? I find it a bit confusing that if > processing is 0 we decrement num_heads_ready in check_ref_cleanup, but > in unselect_delayed_ref_head we set it to 0 and increment it. > >> +} >> + >> /* >> * Helper to insert the ref_node to the tail or merge with tail. >> * >> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h >> index 8e20c5cb5404..d2af974f68a1 100644 >> --- a/fs/btrfs/delayed-ref.h >> +++ b/fs/btrfs/delayed-ref.h >> @@ -261,7 +261,8 @@ static inline void btrfs_delayed_ref_unlock(struct btrfs_delayed_ref_head *head) >> { >> mutex_unlock(&head->mutex); >> } >> - >> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs, >> + struct btrfs_delayed_ref_head *head); >> >> struct btrfs_delayed_ref_head *btrfs_select_ref_head( >> struct btrfs_delayed_ref_root *delayed_refs); >> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c >> index d242a1174e50..c36b3a42f2bb 100644 >> --- a/fs/btrfs/extent-tree.c >> +++ b/fs/btrfs/extent-tree.c >> @@ -2474,12 +2474,9 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans, >> spin_unlock(&delayed_refs->lock); >> return 1; >> } >> - delayed_refs->num_heads--; >> - rb_erase_cached(&head->href_node, &delayed_refs->href_root); >> - RB_CLEAR_NODE(&head->href_node); >> + btrfs_delete_ref_head(delayed_refs, head); >> spin_unlock(&head->lock); >> spin_unlock(&delayed_refs->lock); >> - atomic_dec(&delayed_refs->num_entries); >> >> trace_run_delayed_ref_head(fs_info, head, 0); >> >> @@ -6984,22 +6981,9 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans, >> if (!mutex_trylock(&head->mutex)) >> goto out; >> >> - /* >> - * at this point we have a head with no other entries. Go >> - * ahead and process it. >> - */ >> - rb_erase_cached(&head->href_node, &delayed_refs->href_root); >> - RB_CLEAR_NODE(&head->href_node); >> - atomic_dec(&delayed_refs->num_entries); >> - >> - /* >> - * we don't take a ref on the node because we're removing it from the >> - * tree, so we just steal the ref the tree was holding. >> - */ >> - delayed_refs->num_heads--; >> - if (head->processing == 0) >> - delayed_refs->num_heads_ready--; >> + btrfs_delete_ref_head(delayed_refs, head); >> head->processing = 0; On a closer inspection I think here we can do: ASSERT(head->processing == 0) because at that point we've taken the head->lock spinlock which is held during ordinary delayed refs processing (in __btrfs_run_delayed_refs) when the head is selected (and processing is 1). So head->processing == 0 here I think is a hard invariant of the code. The decrement here should pair with the increment when the head was initially added to the tree. In cleanup_ref_head we don't need to ever worry about num_heads_ready since it has already been decremented by btrfs_select_ref_head. As a matter fact this counter is not used anywhere so we might as well just remove it. > > Something is fishy here, before the code checked for processing == 0 and > then also set it to 0 ? > >> + >> spin_unlock(&head->lock); >> spin_unlock(&delayed_refs->lock); >> >> >