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[209.85.220.65]) by mx.google.com with SMTPS id m18sor8961852ljg.42.2019.06.03.10.35.36 for (Google Transport Security); Mon, 03 Jun 2019 10:35:36 -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=jZtRRCEd; 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=1SfpobffKOrWKpwW04bKR3mmJHzrYDeRfbFX89KU/oE=; b=jZtRRCEdmQBOJG+Z5Up8Wy+HVMsB57ugBkXzh+rkJObgJLdoRJgQKS7nDZimjMzczG S3F4JvOrlWCxkK/z/bDgxnJY6URVrCDeXW239F+/VHZZ81wNElY2v7G1OpQcS5I9wS3V cSf1fcSFeDdhba9fTG2mUs0IncszXpghIDfP4G3Mcxydu7l8apcf6f9nyBvpqQ2e3LB9 +nKxYMfSCIlUDiplICylhbJ8YNz7gYuxTo8xJN4Ru3P+sgTjMWFYTXOe0MptITF/M9Oy beo5KkDFxhWrrHlzSQqKMdwlDCzajLk6/ckQFloacvBIgL6ze5EYrW3BD+mnusYRi1W3 5GZw== X-Google-Smtp-Source: APXvYqxDhmj7CdetUC52G+P/KDdFxFmprc9ZbFMlBQef2Z4kbsNDFuCKau2KhIv26tP0/iKhJ8ROwA== X-Received: by 2002:a2e:9a4f:: with SMTP id k15mr14550155ljj.159.1559583336440; Mon, 03 Jun 2019 10:35:36 -0700 (PDT) Received: from pc636 ([37.139.158.167]) by smtp.gmail.com with ESMTPSA id q11sm3261148lfh.47.2019.06.03.10.35.34 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 03 Jun 2019 10:35:35 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 3 Jun 2019 19:35:28 +0200 To: Roman Gushchin Cc: Uladzislau Rezki , 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: <20190603173528.7ukfgznmiypzfyze@pc636> References: <20190527093842.10701-1-urezki@gmail.com> <20190527093842.10701-5-urezki@gmail.com> <20190528225001.GI27847@tower.DHCP.thefacebook.com> <20190529135817.tr7usoi2xwx5zl2s@pc636> <20190529162638.GB3228@tower.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190529162638.GB3228@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! On Wed, May 29, 2019 at 04:26:43PM +0000, Roman Gushchin wrote: > On Wed, May 29, 2019 at 03:58:17PM +0200, Uladzislau Rezki wrote: > > 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? > > Hello, Uladzislau! > > I don't have a strong opinion here. If you're worried about losing the message, > WARN_ON() should be fine here. I don't think that this event will happen often, > if at all. > If it happens then we are in trouble :) I prefer to keep it here as of now, later on will see. Anyway, let's keep it and i will update it with: if (WARN_ON(RB_EMPTY_NODE(&va->rb_node))) return; Thank you for the comments! -- Vlad Rezki