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[195.135.220.15]) by mx.google.com with ESMTPS id f5si64285edc.177.2019.03.27.04.45.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Mar 2019 04:45:00 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org 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 9BD45AEF5; Wed, 27 Mar 2019 11:44:59 +0000 (UTC) Date: Wed, 27 Mar 2019 12:44:58 +0100 From: Michal Hocko To: Qian Cai 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 Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation Message-ID: <20190327114458.GF11927@dhcp22.suse.cz> References: <20190327005948.24263-1-cai@lca.pw> <20190327084432.GA11927@dhcp22.suse.cz> <651bd879-c8c0-b162-fee7-1e523904b14e@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <651bd879-c8c0-b162-fee7-1e523904b14e@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Wed 27-03-19 07:34:32, Qian Cai wrote: > On 3/27/19 4:44 AM, Michal Hocko wrote: > >> diff --git a/mm/kmemleak.c b/mm/kmemleak.c > >> index a2d894d3de07..7f4545ab1f84 100644 > >> --- a/mm/kmemleak.c > >> +++ b/mm/kmemleak.c > >> @@ -580,7 +580,16 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size, > >> struct rb_node **link, *rb_parent; > >> unsigned long untagged_ptr; > >> > >> - object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp)); > >> + /* > >> + * The tracked memory was allocated successful, if the kmemleak object > >> + * failed to allocate for some reasons, it ends up with the whole > >> + * kmemleak disabled, so try it harder. > >> + */ > >> + gfp = (in_atomic() || irqs_disabled()) ? > >> + gfp_kmemleak_mask(gfp) | GFP_ATOMIC : > >> + gfp_kmemleak_mask(gfp) | __GFP_DIRECT_RECLAIM; > > > > > > The comment for in_atomic says: > > * Are we running in atomic context? WARNING: this macro cannot > > * always detect atomic context; in particular, it cannot know about > > * held spinlocks in non-preemptible kernels. Thus it should not be > > * used in the general case to determine whether sleeping is possible. > > * Do not use in_atomic() in driver code. > > That is why it needs both in_atomic() and irqs_disabled(), so irqs_disabled() > can detect kernel functions held spinlocks even in non-preemptible kernels. > > According to [1], > > "This [2] is useful if you know that the data in question is only ever > manipulated from a "process context", ie no interrupts involved." > > Since kmemleak only deal with kernel context, if a spinlock was held, it always > has local interrupt disabled. 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. > ftrace is in the same boat where this commit was merged a while back that has > the same check. > > ef99b88b16be > tracing: Handle ftrace_dump() atomic context in graph_trace_open() > > [1] https://www.kernel.org/doc/Documentation/locking/spinlocks.txt > [2] > spin_lock(&lock); > ... > spin_unlock(&lock); -- Michal Hocko SUSE Labs