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Fri, 23 Nov 2018 21:58:30 -0500 Received: from mx2.suse.de ([195.135.220.15]:35876 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2436604AbeKXC6a (ORCPT ); Fri, 23 Nov 2018 21:58:30 -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 6753BAE52; Fri, 23 Nov 2018 16:13:38 +0000 (UTC) Subject: Re: [PATCH v2] Btrfs: fix deadlock with memory reclaim during scrub To: fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: <20181123134543.20199-1-fdmanana@kernel.org> <20181123160533.21204-1-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: <9400989f-cc9c-048a-3f37-04c85d0bc569@suse.com> Date: Fri, 23 Nov 2018 18:13:36 +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: <20181123160533.21204-1-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 23.11.18 г. 18:05 ч., fdmanana@kernel.org wrote: > From: Filipe Manana > > When a transaction commit starts, it attempts to pause scrub and it blocks > until the scrub is paused. So while the transaction is blocked waiting for > scrub to pause, we can not do memory allocation with GFP_KERNEL while scrub > is running, we must use GFP_NOS to avoid deadlock with reclaim. Checking > for pause requests is done early in the while loop of scrub_stripe(), and > later in the loop, scrub_extent() is called, which in turns calls > scrub_pages(), which does memory allocations using GFP_KERNEL. So use > GFP_NOFS for the memory allocations because at any time a scrub pause > request can happen from another task that started to commit a transaction. > > Fixes: 58c4e173847a ("btrfs: scrub: use GFP_KERNEL on the submission path") > Signed-off-by: Filipe Manana > --- > > V2: Make using GFP_NOFS unconditionial. Previous version was racy, as pausing > requests migth happen just after we checked for them. > > fs/btrfs/scrub.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c > index 3be1456b5116..0630ea0881bc 100644 > --- a/fs/btrfs/scrub.c > +++ b/fs/btrfs/scrub.c > @@ -2205,7 +2205,13 @@ static int scrub_pages(struct scrub_ctx *sctx, u64 logical, u64 len, > struct scrub_block *sblock; > int index; > > - sblock = kzalloc(sizeof(*sblock), GFP_KERNEL); > + /* > + * In order to avoid deadlock with reclaim when there is a transaction > + * trying to pause scrub, use GFP_NOFS. The pausing request is done when > + * the transaction commit starts, and it blocks the transaction until > + * scrub is paused (done at specific points at scrub_stripe()). > + */ > + sblock = kzalloc(sizeof(*sblock), GFP_NOFS); Newer code shouldn't use GFP_NOFS, rather leave GFP_KERNEL as is and instead use the memaloc_nofs_save/memalloc_nofs_restore. For background information refer to: Documentation/core-api/gfp_mask-from-fs-io.rst > if (!sblock) { > spin_lock(&sctx->stat_lock); > sctx->stat.malloc_errors++; > @@ -2223,7 +2229,7 @@ static int scrub_pages(struct scrub_ctx *sctx, u64 logical, u64 len, > struct scrub_page *spage; > u64 l = min_t(u64, len, PAGE_SIZE); > > - spage = kzalloc(sizeof(*spage), GFP_KERNEL); > + spage = kzalloc(sizeof(*spage), GFP_NOFS); > if (!spage) { > leave_nomem: > spin_lock(&sctx->stat_lock); > @@ -2250,7 +2256,7 @@ static int scrub_pages(struct scrub_ctx *sctx, u64 logical, u64 len, > spage->have_csum = 0; > } > sblock->page_count++; > - spage->page = alloc_page(GFP_KERNEL); > + spage->page = alloc_page(GFP_NOFS); > if (!spage->page) > goto leave_nomem; > len -= l; >