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[195.135.220.15]) by mx.google.com with ESMTPS id f9si1219200edy.321.2019.04.11.01.20.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Apr 2019 01:20:15 -0700 (PDT) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz 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 5D48BAE8A; Thu, 11 Apr 2019 08:20:15 +0000 (UTC) Subject: Re: [PATCH] slab: fix an infinite loop in leaks_show() To: Qian Cai , akpm@linux-foundation.org Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Tobin C. Harding" , Linus Torvalds , Michal Hocko References: <20190411032635.10325-1-cai@lca.pw> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABtCBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PokCVAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJcbbyGBQkH8VTqAAoJECJPp+fMgqZkpGoP /1jhVihakxw1d67kFhPgjWrbzaeAYOJu7Oi79D8BL8Vr5dmNPygbpGpJaCHACWp+10KXj9yz fWABs01KMHnZsAIUytVsQv35DMMDzgwVmnoEIRBhisMYOQlH2bBn/dqBjtnhs7zTL4xtqEcF 1hoUFEByMOey7gm79utTk09hQE/Zo2x0Ikk98sSIKBETDCl4mkRVRlxPFl4O/w8dSaE4eczH LrKezaFiZOv6S1MUKVKzHInonrCqCNbXAHIeZa3JcXCYj1wWAjOt9R3NqcWsBGjFbkgoKMGD usiGabetmQjXNlVzyOYdAdrbpVRNVnaL91sB2j8LRD74snKsV0Wzwt90YHxDQ5z3M75YoIdl byTKu3BUuqZxkQ/emEuxZ7aRJ1Zw7cKo/IVqjWaQ1SSBDbZ8FAUPpHJxLdGxPRN8Pfw8blKY 8mvLJKoF6i9T6+EmlyzxqzOFhcc4X5ig5uQoOjTIq6zhLO+nqVZvUDd2Kz9LMOCYb516cwS/ Enpi0TcZ5ZobtLqEaL4rupjcJG418HFQ1qxC95u5FfNki+YTmu6ZLXy+1/9BDsPuZBOKYpUm 3HWSnCS8J5Ny4SSwfYPH/JrtberWTcCP/8BHmoSpS/3oL3RxrZRRVnPHFzQC6L1oKvIuyXYF rkybPXYbmNHN+jTD3X8nRqo+4Qhmu6SHi3VquQENBFsZNQwBCACuowprHNSHhPBKxaBX7qOv KAGCmAVhK0eleElKy0sCkFghTenu1sA9AV4okL84qZ9gzaEoVkgbIbDgRbKY2MGvgKxXm+kY n8tmCejKoeyVcn9Xs0K5aUZiDz4Ll9VPTiXdf8YcjDgeP6/l4kHb4uSW4Aa9ds0xgt0gP1Xb AMwBlK19YvTDZV5u3YVoGkZhspfQqLLtBKSt3FuxTCU7hxCInQd3FHGJT/IIrvm07oDO2Y8J DXWHGJ9cK49bBGmK9B4ajsbe5GxtSKFccu8BciNluF+BqbrIiM0upJq5Xqj4y+Xjrpwqm4/M ScBsV0Po7qdeqv0pEFIXKj7IgO/d4W2bABEBAAGJA3IEGAEKACYWIQSpQNQ0mSwujpkQPVAi T6fnzIKmZAUCWxk1DAIbAgUJA8JnAAFACRAiT6fnzIKmZMB0IAQZAQoAHRYhBKZ2GgCcqNxn k0Sx9r6Fd25170XjBQJbGTUMAAoJEL6Fd25170XjDBUH/2jQ7a8g+FC2qBYxU/aCAVAVY0NE YuABL4LJ5+iWwmqUh0V9+lU88Cv4/G8fWwU+hBykSXhZXNQ5QJxyR7KWGy7LiPi7Cvovu+1c 9Z9HIDNd4u7bxGKMpn19U12ATUBHAlvphzluVvXsJ23ES/F1c59d7IrgOnxqIcXxr9dcaJ2K k9VP3TfrjP3g98OKtSsyH0xMu0MCeyewf1piXyukFRRMKIErfThhmNnLiDbaVy6biCLx408L Mo4cCvEvqGKgRwyckVyo3JuhqreFeIKBOE1iHvf3x4LU8cIHdjhDP9Wf6ws1XNqIvve7oV+w B56YWoalm1rq00yUbs2RoGcXmtX1JQ//aR/paSuLGLIb3ecPB88rvEXPsizrhYUzbe1TTkKc 4a4XwW4wdc6pRPVFMdd5idQOKdeBk7NdCZXNzoieFntyPpAq+DveK01xcBoXQ2UktIFIsXey uSNdLd5m5lf7/3f0BtaY//f9grm363NUb9KBsTSnv6Vx7Co0DWaxgC3MFSUhxzBzkJNty+2d 10jvtwOWzUN+74uXGRYSq5WefQWqqQNnx+IDb4h81NmpIY/X0PqZrapNockj3WHvpbeVFAJ0 9MRzYP3x8e5OuEuJfkNnAbwRGkDy98nXW6fKeemREjr8DWfXLKFWroJzkbAVmeIL0pjXATxr +tj5JC0uvMrrXefUhXTo0SNoTsuO/OsAKOcVsV/RHHTwCDR2e3W8mOlA3QbYXsscgjghbuLh J3oTRrOQa8tUXWqcd5A0+QPo5aaMHIK0UAthZsry5EmCY3BrbXUJlt+23E93hXQvfcsmfi0N rNh81eknLLWRYvMOsrbIqEHdZBT4FHHiGjnck6EYx/8F5BAZSodRVEAgXyC8IQJ+UVa02QM5 D2VL8zRXZ6+wARKjgSrW+duohn535rG/ypd0ctLoXS6dDrFokwTQ2xrJiLbHp9G+noNTHSan ExaRzyLbvmblh3AAznb68cWmM3WVkceWACUalsoTLKF1sGrrIBj5updkKkzbKOq5gcC5AQ0E Wxk1NQEIAJ9B+lKxYlnKL5IehF1XJfknqsjuiRzj5vnvVrtFcPlSFL12VVFVUC2tT0A1Iuo9 NAoZXEeuoPf1dLDyHErrWnDyn3SmDgb83eK5YS/K363RLEMOQKWcawPJGGVTIRZgUSgGusKL NuZqE5TCqQls0x/OPljufs4gk7E1GQEgE6M90Xbp0w/r0HB49BqjUzwByut7H2wAdiNAbJWZ F5GNUS2/2IbgOhOychHdqYpWTqyLgRpf+atqkmpIJwFRVhQUfwztuybgJLGJ6vmh/LyNMRr8 J++SqkpOFMwJA81kpjuGR7moSrUIGTbDGFfjxmskQV/W/c25Xc6KaCwXah3OJ40AEQEAAYkC PAQYAQoAJhYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJbGTU1AhsMBQkDwmcAAAoJECJPp+fM gqZkPN4P/Ra4NbETHRj5/fM1fjtngt4dKeX/6McUPDIRuc58B6FuCQxtk7sX3ELs+1+w3eSV rHI5cOFRSdgw/iKwwBix8D4Qq0cnympZ622KJL2wpTPRLlNaFLoe5PkoORAjVxLGplvQIlhg miljQ3R63ty3+MZfkSVsYITlVkYlHaSwP2t8g7yTVa+q8ZAx0NT9uGWc/1Sg8j/uoPGrctml hFNGBTYyPq6mGW9jqaQ8en3ZmmJyw3CHwxZ5FZQ5qc55xgshKiy8jEtxh+dgB9d8zE/S/UGI E99N/q+kEKSgSMQMJ/CYPHQJVTi4YHh1yq/qTkHRX+ortrF5VEeDJDv+SljNStIxUdroPD29 2ijoaMFTAU+uBtE14UP5F+LWdmRdEGS1Ah1NwooL27uAFllTDQxDhg/+LJ/TqB8ZuidOIy1B xVKRSg3I2m+DUTVqBy7Lixo73hnW69kSjtqCeamY/NSu6LNP+b0wAOKhwz9hBEwEHLp05+mj 5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: <43517646-a808-bccd-a05e-1b583fc411c7@suse.cz> Date: Thu, 11 Apr 2019 10:20:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190411032635.10325-1-cai@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 4/11/19 5:26 AM, Qian Cai wrote: > "cat /proc/slab_allocators" could hang forever on SMP machines with > kmemleak or object debugging enabled due to other CPUs running do_drain() > will keep making kmemleak_object or debug_objects_cache dirty and unable > to escape the first loop in leaks_show(), So what if we don't remove SLAB (yet?) but start removing the debugging functionality that has been broken for years and nobody noticed. I think Linus already mentioned that we remove at least the /proc/slab_allocators file... > do { > set_store_user_clean(cachep); > drain_cpu_caches(cachep); > ... > > } while (!is_store_user_clean(cachep)); > > For example, > > do_drain > slabs_destroy > slab_destroy > kmem_cache_free > __cache_free > ___cache_free > kmemleak_free_recursive > delete_object_full > __delete_object > put_object > free_object_rcu > kmem_cache_free > cache_free_debugcheck --> dirty kmemleak_object > > One approach is to check cachep->name and skip both kmemleak_object and > debug_objects_cache in leaks_show(). The other is to set > store_user_clean after drain_cpu_caches() which leaves a small window > between drain_cpu_caches() and set_store_user_clean() where per-CPU > caches could be dirty again lead to slightly wrong information has been > stored but could also speed up things significantly which sounds like a > good compromise. For example, > > # cat /proc/slab_allocators > 0m42.778s # 1st approach > 0m0.737s # 2nd approach > > Fixes: d31676dfde25 ("mm/slab: alternative implementation for DEBUG_SLAB_LEAK") > Signed-off-by: Qian Cai > --- > mm/slab.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/slab.c b/mm/slab.c > index 9142ee992493..3e1b7ff0360c 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -4328,8 +4328,12 @@ static int leaks_show(struct seq_file *m, void *p) > * whole processing. > */ > do { > - set_store_user_clean(cachep); > drain_cpu_caches(cachep); > + /* > + * drain_cpu_caches() could always make kmemleak_object and > + * debug_objects_cache dirty, so reset afterwards. > + */ > + set_store_user_clean(cachep); > > x[1] = 0; > >