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Mon, 19 Nov 2018 15:19:01 -0500 Received: from mx2.suse.de ([195.135.220.15]:34652 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727084AbeKSUTB (ORCPT ); Mon, 19 Nov 2018 15:19:01 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 91152AACA; Mon, 19 Nov 2018 09:55:51 +0000 (UTC) Subject: Re: [PATCH] Btrfs: fix access to available allocation bits when starting balance To: fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: <20181119094812.27296-1-fdmanana@kernel.org> From: Nikolay Borisov 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: Date: Mon, 19 Nov 2018 11:55:50 +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: <20181119094812.27296-1-fdmanana@kernel.org> 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 19.11.18 г. 11:48 ч., fdmanana@kernel.org wrote: > From: Filipe Manana > > The available allocation bits members from struct btrfs_fs_info are > protected by a sequence lock, and when starting balance we access them > incorrectly in two different ways: > > 1) In the read sequence lock loop at btrfs_balance() we use the values we > read from fs_info->avail_*_alloc_bits and we can immediately do actions > that have side effects and can not be undone (printing a message and > jumping to a label). This is wrong because a retry might be needed, so > our actions must not have side effects and must be repeatable as long > as read_seqretry() returns a non-zero value. In other words, we were > essentially ignoring the sequence lock; > > 2) Right below the read sequence lock loop, we were reading the values > from avail_metadata_alloc_bits and avail_data_alloc_bits without any > protection from concurrent writers, that is, reading them outside of > the read sequence lock critical section. > > So fix this by making sure we only read the available allocation bits > while in a read sequence lock critical section and that what we do in the > critical section is repeatable (has nothing that can not be undone) so > that any eventual retry that is needed is handled properly. > > Fixes: de98ced9e743 ("Btrfs: use seqlock to protect fs_info->avail_{data, metadata, system}_alloc_bits") > Fixes: 14506127979a ("btrfs: fix a bogus warning when converting only data or metadata") > Signed-off-by: Filipe Manana Reviewed-by: Nikolay Borisov > --- > fs/btrfs/volumes.c | 39 +++++++++++++++++++++++---------------- > 1 file changed, 23 insertions(+), 16 deletions(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index f4405e430da6..223334f08530 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -3712,6 +3712,7 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, > int ret; > u64 num_devices; > unsigned seq; > + bool reducing_integrity; > > if (btrfs_fs_closing(fs_info) || > atomic_read(&fs_info->balance_pause_req) || > @@ -3796,24 +3797,30 @@ int btrfs_balance(struct btrfs_fs_info *fs_info, > !(bctl->sys.target & allowed)) || > ((bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) && > (fs_info->avail_metadata_alloc_bits & allowed) && > - !(bctl->meta.target & allowed))) { > - if (bctl->flags & BTRFS_BALANCE_FORCE) { > - btrfs_info(fs_info, > - "balance: force reducing metadata integrity"); > - } else { > - btrfs_err(fs_info, > - "balance: reduces metadata integrity, use --force if you want this"); > - ret = -EINVAL; > - goto out; > - } > - } > + !(bctl->meta.target & allowed))) > + reducing_integrity = true; > + else > + reducing_integrity = false; > + > + /* if we're not converting, the target field is uninitialized */ > + meta_target = (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) ? > + bctl->meta.target : fs_info->avail_metadata_alloc_bits; > + data_target = (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) ? > + bctl->data.target : fs_info->avail_data_alloc_bits; > } while (read_seqretry(&fs_info->profiles_lock, seq)); > > - /* if we're not converting, the target field is uninitialized */ > - meta_target = (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) ? > - bctl->meta.target : fs_info->avail_metadata_alloc_bits; > - data_target = (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) ? > - bctl->data.target : fs_info->avail_data_alloc_bits; > + if (reducing_integrity) { > + if (bctl->flags & BTRFS_BALANCE_FORCE) { > + btrfs_info(fs_info, > + "balance: force reducing metadata integrity"); > + } else { > + btrfs_err(fs_info, > + "balance: reduces metadata integrity, use --force if you want this"); > + ret = -EINVAL; > + goto out; > + } > + } > + > if (btrfs_get_num_tolerated_disk_barrier_failures(meta_target) < > btrfs_get_num_tolerated_disk_barrier_failures(data_target)) { > int meta_index = btrfs_bg_flags_to_raid_index(meta_target); >