linux-kernel - Re: Coverity: zblock_reclaim_block(): Control flow issues

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Message-ID: <Y3bMTK+558whA1VX@work>
Date:   Thu, 17 Nov 2022 18:05:32 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     coverity-bot <keescook@...omium.org>
Cc:     Ananda <a.badmaev@...cknet.pro>, Jonathan Corbet <corbet@....net>,
        linux-kernel@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-mm@...ck.org, linux-doc@...r.kernel.org,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-next@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: Coverity: zblock_reclaim_block(): Control flow issues

On Thu, Nov 17, 2022 at 02:21:46PM -0800, coverity-bot wrote:
> Hello!
> 
> This is an experimental semi-automated report about issues detected by
> Coverity from a scan of next-20221117 as part of the linux-next scan project:
> https://scan.coverity.com/projects/linux-next-weekly-scan
> 
> You're getting this email because you were associated with the identified
> lines of code (noted below) that were touched by commits:
> 
>   Wed Nov 16 16:19:12 2022 -0800
>     9097e28c25c8 ("mm: add zblock - new allocator for use via zpool API")
> 
> Coverity reported the following:
> 
> *** CID 1527349:  Control flow issues  (NO_EFFECT)
> mm/zblock.c:412 in zblock_reclaim_block()
> 406     	unsigned long handle, block_type, slot;
> 407     	int ret, i, reclaimed;
> 408
> 409     	/* start with list storing blocks with the worst compression and try
> 410     	 * to evict the first added (oldest) block in this list
> 411     	 */
> vvv     CID 1527349:  Control flow issues  (NO_EFFECT)
> vvv     This greater-than-or-equal-to-zero comparison of an unsigned value is always true. "block_type >= 0UL".
> 412     	for (block_type = ARRAY_SIZE(block_desc) - 1; block_type >= 0; --block_type) {

This seems like a legit issue.

--
Gustavo

> 413     		list = &(pool->block_lists[block_type]);
> 414     		spin_lock(&list->lock);
> 415
> 416     		/* find the oldest block in list */
> 417     		block = list_last_entry(&list->head, struct zblock_block, block_node);
> 
> If this is a false positive, please let us know so we can mark it as
> such, or teach the Coverity rules to be smarter. If not, please make
> sure fixes get into linux-next. :) For patches fixing this, please
> include these lines (but double-check the "Fixes" first):
> 
> Reported-by: coverity-bot <keescook+coverity-bot@...omium.org>
> Addresses-Coverity-ID: 1527349 ("Control flow issues")
> Fixes: 9097e28c25c8 ("mm: add zblock - new allocator for use via zpool API")
> 
> Thanks for your attention!
> 
> -- 
> Coverity-bot