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[198.145.29.99]) by mx.google.com with ESMTPS id f1si1137900pgi.432.2019.06.18.13.59.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 Jun 2019 13:59:22 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=dRPi+E6V; spf=pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 57C2C20863; Tue, 18 Jun 2019 20:59:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560891562; bh=OKekjAHMHDSKBX7i8AEyG++qk2Jq9H3Y71jv2y4IdLU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dRPi+E6V6BOa4jcRdwiJTpkttXzbzF7JzL+etbTckkndfBqAq8OEfjCMcljvaUl5A Y0dguz5W/QAQY/rZu34ZBxhJDhgFbNBRj3YPGSV5CsXkQLhMnGgPxgOMaInyd2e2yY /VadGoXzYEJuUjtFcTrb9+vrKqIoxTcf+93+SKaU= Date: Tue, 18 Jun 2019 13:59:20 -0700 From: Andrew Morton To: Uladzislau Rezki Cc: Joel Fernandes , Arnd Bergmann , Roman Penyaev , "open list:MEMORY MANAGEMENT" , Roman Gushchin , Michal Hocko , Matthew Wilcox , Thomas Garnier , Oleksiy Avramchenko , Steven Rostedt , Thomas Gleixner , Ingo Molnar , Tejun Heo , Linus Torvalds , Rick Edgecombe , Andrey Ryabinin , Mike Rapoport , LKML Subject: Re: [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning Message-Id: <20190618135920.9dd7bdc78fc0ce33ee65d99c@linux-foundation.org> In-Reply-To: <20190618140622.bbak3is7yv32hfjn@pc636> References: <20190618092650.2943749-1-arnd@arndb.de> <20190618140622.bbak3is7yv32hfjn@pc636> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 Tue, 18 Jun 2019 16:06:22 +0200 Uladzislau Rezki wrote: > On Tue, Jun 18, 2019 at 09:40:28AM -0400, Joel Fernandes wrote: > > On Tue, Jun 18, 2019 at 5:27 AM Arnd Bergmann wrote: > > > > > > gcc gets confused in pcpu_get_vm_areas() because there are too many > > > branches that affect whether 'lva' was initialized before it gets > > > used: > > > > > > mm/vmalloc.c: In function 'pcpu_get_vm_areas': > > > mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized] > > > insert_vmap_area_augment(lva, &va->rb_node, > > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > &free_vmap_area_root, &free_vmap_area_list); > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > mm/vmalloc.c:916:20: note: 'lva' was declared here > > > struct vmap_area *lva; > > > ^~~ > > > > > > Add an intialization to NULL, and check whether this has changed > > > before the first use. > > > > > > Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation") > > > Signed-off-by: Arnd Bergmann > > > --- > > > mm/vmalloc.c | 9 +++++++-- > > > 1 file changed, 7 insertions(+), 2 deletions(-) > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > index a9213fc3802d..42a6f795c3ee 100644 > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > > @@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va, > > > unsigned long nva_start_addr, unsigned long size, > > > enum fit_type type) > > > { > > > - struct vmap_area *lva; > > > + /* > > > + * GCC cannot always keep track of whether this variable > > > + * was initialized across many branches, therefore set > > > + * it NULL here to avoid a warning. > > > + */ > > > + struct vmap_area *lva = NULL; > > > > Fair enough, but is this 5-line comment really needed here? > > > How it is rewritten now, probably not. I would just set it NULL and > leave the comment, but that is IMHO. Anyway > I agree - given that the patch does this: @@ -972,7 +977,7 @@ adjust_va_to_fit_type(struct vmap_area * if (type != FL_FIT_TYPE) { augment_tree_propagate_from(va); - if (type == NE_FIT_TYPE) + if (lva) insert_vmap_area_augment(lva, &va->rb_node, &free_vmap_area_root, &free_vmap_area_list); } the comment simply isn't relevant any more. Although I guess this might be a bit helpful: @@ -977,7 +972,7 @@ adjust_va_to_fit_type(struct vmap_area * if (type != FL_FIT_TYPE) { augment_tree_propagate_from(va); - if (lva) + if (lva) /* type == NE_FIT_TYPE */ insert_vmap_area_augment(lva, &va->rb_node, &free_vmap_area_root, &free_vmap_area_list); }