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[209.85.220.65]) by mx.google.com with SMTPS id 3sor565237wrs.49.2019.02.13.17.51.07 for (Google Transport Security); Wed, 13 Feb 2019 17:51:07 -0800 (PST) Received-SPF: pass (google.com: domain of surenb@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=vSAH0Rpc; spf=pass (google.com: domain of surenb@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=F24RVbeKKB1cnCpDEq5tv60PU/vFe4EDFYXQPFBYiG4=; b=vSAH0RpcqZoI384N6aWx/a6ZO2VP1uD+NDCUhuF485R1ktTjgbuR4PWJN1jDtxgthv tpuxVzwCTlSEem19lNbbjRd64NWiI9+H6gVoVdOXse39STXrhIByIAXR29cbksE5hDeC XDzgSzzrFoubIeuv61vg5LzUDm/AuQA4Xu03E2eYI9EmAfExE4qrbEENk6rXge3HAWll yk+QSMLSZoH9LNhMKxKRUJrev4N4BQU22lVhPXu6d7xlfHHX0HTrpCxsEuitSs+riyGW xPyFR4EXHqRBAEPYUcJ2+Tz9aB+EKuX81RkV5ag74cXkyQ1IH4W3dS6RONT25M15qXXs +74w== X-Google-Smtp-Source: AHgI3IawV0AoL7/SiLAiW/evEF+BYLElakf4/oiB4CxjF1FDKzc7cBvow+JY0LNl96CjfAcJTQ9o3oVFmLRng1RtSqs= X-Received: by 2002:adf:dbc4:: with SMTP id e4mr748458wrj.320.1550109066968; Wed, 13 Feb 2019 17:51:06 -0800 (PST) MIME-Version: 1.0 References: <201902080231.RZbiWtQ6%fengguang.wu@intel.com> <20190208151441.4048e6968579dd178b259609@linux-foundation.org> <20190209074407.GE4240@linux.ibm.com> <20190212013606.GJ12668@bombadil.infradead.org> <20190212163145.GD14231@cmpxchg.org> <20190212163547.GP12668@bombadil.infradead.org> In-Reply-To: <20190212163547.GP12668@bombadil.infradead.org> From: Suren Baghdasaryan Date: Wed, 13 Feb 2019 17:50:55 -0800 Message-ID: Subject: Re: [linux-next:master 6618/6917] kernel/sched/psi.c:1230:13: sparse: error: incompatible types in comparison expression (different address spaces) To: Matthew Wilcox Cc: Johannes Weiner , "Paul E. McKenney" , Andrew Morton , kbuild test robot , kbuild-all@01.org, Linux Memory Management List Content-Type: text/plain; charset="UTF-8" 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 Tue, Feb 12, 2019 at 8:35 AM Matthew Wilcox wrote: > > On Tue, Feb 12, 2019 at 11:31:45AM -0500, Johannes Weiner wrote: > > On Mon, Feb 11, 2019 at 05:36:06PM -0800, Matthew Wilcox wrote: > > > On Fri, Feb 08, 2019 at 11:44:07PM -0800, Paul E. McKenney wrote: > > > > On Fri, Feb 08, 2019 at 03:14:41PM -0800, Andrew Morton wrote: > > > > > On Fri, 8 Feb 2019 02:29:33 +0800 kbuild test robot wrote: > > > > > > 1223 static __poll_t psi_fop_poll(struct file *file, poll_table *wait) > > > > > > 1224 { > > > > > > 1225 struct seq_file *seq = file->private_data; > > > > > > 1226 struct psi_trigger *t; > > > > > > 1227 __poll_t ret; > > > > > > 1228 > > > > > > 1229 rcu_read_lock(); > > > > > > > 1230 t = rcu_dereference(seq->private); > > > > > > So the problem here is the opposite of what we think it is -- seq->private > > > is not marked as being RCU protected. > > > > > > > If you wish to opt into this checking, you need to mark the pointer > > > > definitions (in this case ->private) with __rcu. It may also > > > > be necessary to mark function parameters as well, as is done for > > > > radix_tree_iter_resume(). If you do not wish to use this checking, > > > > you should ignore these sparse warnings. > > > > We cannot make struct seq_file->private generally __rcu, but the > > cgroup code has a similar thing with kernfs, where it's doing rcu for > > its particular use of struct kernfs_node->private. This is how it does > > the dereference: > > > > cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv); > > > > We could do this here as well. > > > > It's ugly, though. I'd also be fine with ignoring the sparse warning. > > How about: > > +++ b/include/linux/seq_file.h > @@ -26,7 +26,10 @@ struct seq_file { > const struct seq_operations *op; > int poll_event; > const struct file *file; > - void *private; > + union { > + void *private; > + void __rcu *rcu_private; > + }; > }; > > struct seq_operations { > Personally I would prefer cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv); as it's more localized change but if union would be preferable I'll roll that into the next version of psi monitor. Thanks, Suren.