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From: Gao Xiang <hsiangkao@aol.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>,
	linux-xfs@vger.kernel.org, Gao Xiang <gaoxiang25@huawei.com>,
	William Kucharski <william.kucharski@oracle.com>,
	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 <dchinner@redhat.com>,
	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
Date: Tue, 21 Apr 2020 15:28:51 +0800
Message-ID: <20200421072839.GA13867@hsiangkao-HP-ZHAN-66-Pro-G1> (raw)
In-Reply-To: <20200420224210.dff005bc62957a4d81d58226@linux-foundation.org>

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 <willy@infradead.org> 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



  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-14 15:02 [PATCH v11 00/25] Change readahead API Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 01/25] mm: Move readahead prototypes from mm.h Matthew Wilcox
2020-04-15  9:10   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 02/25] mm: Return void from various readahead functions Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 03/25] mm: Ignore return value of ->readpages Matthew Wilcox
2020-04-15  9:17   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 04/25] mm: Move readahead nr_pages check into read_pages Matthew Wilcox
2020-04-15  9:19   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 05/25] mm: Add new readahead_control API Matthew Wilcox
2020-04-15  1:17   ` Andrew Morton
2020-04-15  2:18     ` Matthew Wilcox
2020-04-15  4:56       ` Andrew Morton
2020-04-15 11:22         ` Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 06/25] mm: Use readahead_control to pass arguments Matthew Wilcox
2020-04-15  9:30   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 07/25] mm: Rename various 'offset' parameters to 'index' Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 08/25] mm: rename readahead loop variable to 'i' Matthew Wilcox
2020-04-15  9:31   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 09/25] mm: Remove 'page_offset' from readahead loop Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 10/25] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 11/25] mm: Add readahead address space operation Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 12/25] mm: Move end_index check out of readahead loop Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 13/25] mm: Add page_cache_readahead_unbounded Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 14/25] mm: Document why we don't set PageReadahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 15/25] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 16/25] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-06-16 22:36   ` [Cluster-devel] " Andreas Gruenbacher
2020-06-17  0:32     ` Matthew Wilcox
2020-06-17  0:57       ` Andreas Grünbacher
2020-06-17  2:21         ` Matthew Wilcox
2020-06-18 12:46           ` Andreas Gruenbacher
2020-06-18 15:03             ` Matthew Wilcox
2020-06-18 16:40               ` Andreas Gruenbacher
2020-04-14 15:02 ` [PATCH v11 17/25] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 18/25] erofs: Convert uncompressed files " Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 19/25] erofs: Convert compressed " Matthew Wilcox
2020-04-21  5:42   ` Andrew Morton
2020-04-21  7:28     ` Gao Xiang [this message]
2020-04-14 15:02 ` [PATCH v11 20/25] ext4: Convert " Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 21/25] ext4: Pass the inode to ext4_mpage_readpages Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 22/25] f2fs: Convert from readpages to readahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 23/25] f2fs: Pass the inode to f2fs_mpage_readpages Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 24/25] fuse: Convert from readpages to readahead Matthew Wilcox
2020-04-20 11:14   ` Miklos Szeredi
2020-04-20 11:43     ` Matthew Wilcox
2020-04-20 11:54       ` Miklos Szeredi
2020-04-14 15:02 ` [PATCH v11 25/25] iomap: " Matthew Wilcox

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