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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id z20sm5101396qkb.52.2019.03.27.06.05.33 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Mar 2019 06:05:33 -0700 (PDT) Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation To: Michal Hocko Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, cl@linux.com, willy@infradead.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190327005948.24263-1-cai@lca.pw> <20190327084432.GA11927@dhcp22.suse.cz> <651bd879-c8c0-b162-fee7-1e523904b14e@lca.pw> <20190327114458.GF11927@dhcp22.suse.cz> From: Qian Cai Message-ID: <68cff59d-2b0e-5a7b-bca9-36784522059b@lca.pw> Date: Wed, 27 Mar 2019 09:05:31 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.3.3 MIME-Version: 1.0 In-Reply-To: <20190327114458.GF11927@dhcp22.suse.cz> 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 3/27/19 7:44 AM, Michal Hocko wrote> What? Normal spin lock implementation doesn't disable interrupts. So > either I misunderstand what you are saying or you seem to be confused. > the thing is that in_atomic relies on preempt_count to work properly and > if you have CONFIG_PREEMPT_COUNT=n then you simply never know whether > preemption is disabled so you do not know that a spin_lock is held. > irqs_disabled on the other hand checks whether arch specific flag for > IRQs handling is set (or cleared). So you would only catch irq safe spin > locks with the above check. Exactly, because kmemleak_alloc() is only called in a few call sites, slab allocation, neigh_hash_alloc(), alloc_page_ext(), sg_kmalloc(), early_amd_iommu_init() and blk_mq_alloc_rqs(), my review does not yield any of those holding irq unsafe spinlocks. Could future code changes suddenly call kmemleak_alloc() with a irq unsafe spinlock held? Always possible, but it is unlikely to happen. I could put some comments on kmemleak_alloc() about this though.