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[209.85.220.65]) by mx.google.com with SMTPS id a5sor2726047ljf.4.2019.05.29.06.58.26 for (Google Transport Security); Wed, 29 May 2019 06:58:27 -0700 (PDT) Received-SPF: pass (google.com: domain of urezki@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=uXjwPjRZ; spf=pass (google.com: domain of urezki@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=urezki@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=FvnuOzvWWHxvWxRXVyec6ngD8uETWcADOgiOUZyOXOI=; b=uXjwPjRZCt5+NzEnNPmdCCkF3iYjQdmKQjzHPmIBvcHk21+tVcQk6R/TffAC7mbzK7 3OwgsrDjSkovmg4CpeCxkjLO/kQQvYs0pmQohCNI7L8gZdD8RGrfY4VGJdYTU4SoFB3v vxOJmH2NmOUBLSaEMsTV4T0d7uI//nBlM9nMZjIItiftF4IVJAOz7r5HkBkNRO1ocej9 uSw6MboF7GCpcr9BVSt1oVeMNInBa+xY8WKUwIpqaSATf3Ri/vgGphqjpJDKCfIuJNPw 2XVz/73HtiI5Ls00TDoUhrA2TsMBVDDDh2a2MIgaAD8+i7k63TUUX87Zz6QC0oBlSFQ1 qdNA== X-Google-Smtp-Source: APXvYqxJcXNy9tjvGvb6p0Lmjk07Ff52IXEus1xxpwJYnnL8XqCx75U51Gw9O4dVXAeZBa+45pmDaQ== X-Received: by 2002:a2e:a0ca:: with SMTP id f10mr1708409ljm.113.1559138306581; Wed, 29 May 2019 06:58:26 -0700 (PDT) Received: from pc636 ([37.139.158.167]) by smtp.gmail.com with ESMTPSA id d18sm3473580lfl.95.2019.05.29.06.58.24 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 29 May 2019 06:58:25 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 29 May 2019 15:58:17 +0200 To: Roman Gushchin Cc: "Uladzislau Rezki (Sony)" , Andrew Morton , "linux-mm@kvack.org" , Hillf Danton , Michal Hocko , Matthew Wilcox , LKML , Thomas Garnier , Oleksiy Avramchenko , Steven Rostedt , Joel Fernandes , Thomas Gleixner , Ingo Molnar , Tejun Heo Subject: Re: [PATCH v3 4/4] mm/vmap: move BUG_ON() check to the unlink_va() Message-ID: <20190529135817.tr7usoi2xwx5zl2s@pc636> References: <20190527093842.10701-1-urezki@gmail.com> <20190527093842.10701-5-urezki@gmail.com> <20190528225001.GI27847@tower.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190528225001.GI27847@tower.DHCP.thefacebook.com> User-Agent: NeoMutt/20170113 (1.7.2) 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: Hello, Roman! > > Move the BUG_ON()/RB_EMPTY_NODE() check under unlink_va() > > function, it means if an empty node gets freed it is a BUG > > thus is considered as faulty behaviour. > > It's not exactly clear from the description, why it's better. > It is rather about if "unlink" happens on unhandled node it is faulty behavior. Something that clearly written in stone. We used to call "unlink" on detached node during merge, but after: [PATCH v3 3/4] mm/vmap: get rid of one single unlink_va() when merge it is not supposed to be ever happened across the logic. > > Also, do we really need a BUG_ON() in either place? > Historically we used to have the BUG_ON there. We can get rid of it for sure. But in this case, it would be harder to find a head or tail of it when the crash occurs, soon or later. > Isn't something like this better? > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index c42872ed82ac..2df0e86d6aff 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1118,7 +1118,8 @@ EXPORT_SYMBOL_GPL(unregister_vmap_purge_notifier); > > static void __free_vmap_area(struct vmap_area *va) > { > - BUG_ON(RB_EMPTY_NODE(&va->rb_node)); > + if (WARN_ON_ONCE(RB_EMPTY_NODE(&va->rb_node))) > + return; > I was thinking about WARN_ON_ONCE. The concern was about if the message gets lost due to kernel ring buffer. Therefore i used that. I am not sure if we have something like WARN_ONE_RATELIMIT that would be the best i think. At least it would indicate if a warning happens periodically or not. Any thoughts? Thanks for the comments! -- Vlad Rezki