From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id B77AA6B0033 for ; Tue, 17 Jan 2017 16:42:36 -0500 (EST) Received: by mail-pg0-f70.google.com with SMTP id z67so139847159pgb.0 for ; Tue, 17 Jan 2017 13:42:36 -0800 (PST) Received: from mga02.intel.com (mga02.intel.com. [134.134.136.20]) by mx.google.com with ESMTPS id g1si26107130pgc.92.2017.01.17.13.42.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Jan 2017 13:42:35 -0800 (PST) Date: Tue, 17 Jan 2017 13:42:35 -0800 From: Tim Chen Subject: Re: [Update][PATCH v5 7/9] mm/swap: Add cache for swap slots allocation Message-ID: <20170117214234.GA14383@linux.intel.com> Reply-To: tim.c.chen@linux.intel.com References: <35de301a4eaa8daa2977de6e987f2c154385eb66.1484082593.git.tim.c.chen@linux.intel.com> <87tw8ymm2z.fsf_-_@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="vkogqOf2sHV7VnPd" Content-Disposition: inline In-Reply-To: <87tw8ymm2z.fsf_-_@yhuang-dev.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Huang, Ying" Cc: Andrew Morton , dave.hansen@intel.com, ak@linux.intel.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Shaohua Li , Minchan Kim , Rik van Riel , Andrea Arcangeli , "Kirill A . Shutemov" , Vladimir Davydov , Johannes Weiner , Michal Hocko , Hillf Danton , Christian Borntraeger , Jonathan Corbet , Tim C Chen --vkogqOf2sHV7VnPd Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Jan 17, 2017 at 10:55:47AM +0800, Huang, Ying wrote: > Hi, Andrew, >=20 > This update patch is to fix the preemption warning raised by Michal > Hocko. raw_cpu_ptr() is used to replace this_cpu_ptr() and comments are > added for why it is used. >=20 Andrew & Michal, Here's a fix that's a follow on patch instead of an updated patch as Michal has suggested. I've updated the comments a bit to make it clearer. Thanks. Tim --->8--- Date: Tue, 17 Jan 2017 12:57:00 -0800 Subject: [PATCH] mm/swap: Use raw_cpu_ptr over this_cpu_ptr for swap slots access To: Andrew Morton Cc: Ying Huang , dave.hansen@intel.com, ak@linux.inte= l.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org= , Hugh Dickins , Shaohua Li , Minchan Ki= m , Rik van Riel , Andrea Arcangeli , Kirill A . Shutemov ,= Vladimir Davydov , Johannes Weiner , Michal Hocko , Hillf Danton , Christian Borntraeger , Jonathan Corbet =46rom: "Huang, Ying" The usage of this_cpu_ptr in get_swap_page causes a bug warning as it is used in pre-emptible code. [ 57.812314] BUG: using smp_processor_id() in preemptible [00000000] code= : kswapd0/527 [ 57.814360] caller is debug_smp_processor_id+0x17/0x19 [ 57.815237] CPU: 1 PID: 527 Comm: kswapd0 Tainted: G W 4.9.0-mmot= m-00135-g4e9a9895ebef #1042 [ 57.816019] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS = 1.10.1-1 04/01/2014 [ 57.816019] ffffc900001939c0 ffffffff81329c60 0000000000000001 ffffffff= 81a0ce06 [ 57.816019] ffffc900001939f0 ffffffff81343c2a 00000000000137a0 ffffea00= 00dfd2a0 [ 57.816019] ffff88003c49a700 ffffc90000193b10 ffffc90000193a00 ffffffff= 81343c53 [ 57.816019] Call Trace: [ 57.816019] [] dump_stack+0x68/0x92 [ 57.816019] [] check_preemption_disabled+0xce/0xe0 [ 57.816019] [] debug_smp_processor_id+0x17/0x19 [ 57.816019] [] get_swap_page+0x19/0x183 [ 57.816019] [] shmem_writepage+0xce/0x38c [ 57.816019] [] shrink_page_list+0x81f/0xdbf [ 57.816019] [] shrink_inactive_list+0x2ab/0x594 [ 57.816019] [] shrink_node_memcg+0x4c7/0x673 [ 57.816019] [] shrink_node+0xc4/0x282 [ 57.816019] [] ? shrink_node+0xc4/0x282 [ 57.816019] [] kswapd+0x656/0x834 Logic wise, We do allow pre-emption as per cpu ptr cache->slots is protected by the mutex cache->alloc_lock. We switch the inappropriately used this_cpu_ptr to raw_cpu_ptr for per cpu ptr access of cache->slots. Reported-by: Michal Hocko Signed-off-by: "Huang, Ying" Signed-off-by: Tim Chen --- mm/swap_slots.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/swap_slots.c b/mm/swap_slots.c index 8cf941e..9b5bc86 100644 --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -303,7 +303,16 @@ swp_entry_t get_swap_page(void) swp_entry_t entry, *pentry; struct swap_slots_cache *cache; =20 - cache =3D this_cpu_ptr(&swp_slots); + /* + * Preemption is allowed here, because we may sleep + * in refill_swap_slots_cache(). But it is safe, because + * accesses to the per-CPU data structure are protected by the + * mutex cache->alloc_lock. + * + * The alloc path here does not touch cache->slots_ret + * so cache->free_lock is not taken. + */ + cache =3D raw_cpu_ptr(&swp_slots); =20 entry.val =3D 0; if (check_cache_active()) { --=20 2.5.5 --vkogqOf2sHV7VnPd Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBAgAGBQJYfo/KAAoJEKJntYqi1rhJMU8QAKlUQOzi7jp8od1tdH/7A+Qh R6quSzU3d4sUUlX4o1eA4FCeFFqTKrAJozAury1869ZBwnoswR1J0Jq9sBZQCxrP bvf4XAHC0oa4faUFgWYuEMx0N6Sh3j1EQBKAdupveffV9NUA2MQf7choNPi9bWKF fWIwOThmO7CPQ/3XmpP2kdvzYIfqqpMVvGdpfGlL1qMd8W8HH36d5y1leo7GtmET Fs/n5FQTFYOEXyrz1fnNcpCvOjpWcMDMNJtj0yenPLyUCJJxLVgyNkOBXMfbxCA9 WTSWXA0KhX/qK4sr4bIX7bVsfOgQdVWkzF09nnLCG7XA6laV4H+EXQgExAr3feso LJ3mI7ieQfzrDTuV/q21MqNQMs7UvDitjk4yhhmQW4bsYv5tZRbSLad9BRXYQI0t HpkGoBpWaoB1OvNyzBo8nUK276XCRLIMkvMYK9YxdupEwupQvngu5CxBCBYUoUdZ u0uq+pwlZl83Mfu/YV+7OAbq83MnFK2PqzL9tpi4+vqtAZoybTrwBexhTilYGl6C B76nGQhaN8jX20j7ECPIh/afcXHo51LAi4ifW6YQhTnVKFVVc2+TFvAD5a3D+CRD A0R9klL+PXRDIAX39g7vlEAg3wsA8iNHu871zFYju295DbHzdz/ktMIFkcixOTZf 8Xi0QOCixeujF2w/82mN =CuaE -----END PGP SIGNATURE----- --vkogqOf2sHV7VnPd-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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