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Tue, 21 Apr 2020 07:31:01 +0000 Received: by smtp407.mail.gq1.yahoo.com (VZM Hermes SMTP Server) with ESMTPA ID 98aed6c61d98e300b5dca39559149029; Tue, 21 Apr 2020 07:28:59 +0000 (UTC) Date: Tue, 21 Apr 2020 15:28:51 +0800 From: Gao Xiang To: Andrew Morton Cc: Matthew Wilcox , linux-xfs@vger.kernel.org, Gao Xiang , William Kucharski , linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, ocfs2-devel@oss.oracle.com, Dave Chinner , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Subject: Re: [PATCH v11 19/25] erofs: Convert compressed files from readpages to readahead Message-ID: <20200421072839.GA13867@hsiangkao-HP-ZHAN-66-Pro-G1> References: <20200414150233.24495-1-willy@infradead.org> <20200414150233.24495-20-willy@infradead.org> <20200420224210.dff005bc62957a4d81d58226@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200420224210.dff005bc62957a4d81d58226@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Mailer: WebService/1.1.15739 hermes Apache-HttpAsyncClient/4.1.4 (Java/11.0.6) 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: Hi Andrew, On Mon, Apr 20, 2020 at 10:42:10PM -0700, Andrew Morton wrote: > On Tue, 14 Apr 2020 08:02:27 -0700 Matthew Wilcox wrote: > > > > > Use the new readahead operation in erofs. > > > > Well this is exciting. > > fs/erofs/data.c: In function erofs_raw_access_readahead: > fs/erofs/data.c:149:18: warning: last_block may be used uninitialized in this function [-Wmaybe-uninitialized] > *last_block + 1 != current_block) { > > It seems to be a preexisting bug, which your patch prompted gcc-7.2.0 > to notice. > > erofs_read_raw_page() goes in and uses *last_block, but neither of its > callers has initialized it. Could the erofs maintainers please take a > look? simply because last_block doesn't need to be initialized at first, because bio == NULL in the begining anyway. I believe this is a gcc false warning because some gcc versions raised some before (many gccs don't, including my current gcc (Debian 8.3.0-6) 8.3.0). in detail, 146 /* note that for readpage case, bio also equals to NULL */ 147 if (bio && 148 /* not continuous */ 149 *last_block + 1 != current_block) { 150 submit_bio_retry: 151 submit_bio(bio); 152 bio = NULL; 153 } bio will be NULL and will bypass the next condition at first. after that, 155 if (!bio) { ... 221 bio = bio_alloc(GFP_NOIO, nblocks); ... } ... 230 err = bio_add_page(bio, page, PAGE_SIZE, 0); 231 /* out of the extent or bio is full */ 232 if (err < PAGE_SIZE) 233 goto submit_bio_retry; 234 235 *last_block = current_block; so bio != NULL, and last_block will be assigned then as well. Thanks, Gao Xiang