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	Wed, 18 Jun 2025 17:47:57 +0000
Date: Wed, 18 Jun 2025 18:47:57 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Dan Carpenter <dan.carpenter@linaro.org>
Cc: oe-kbuild@lists.linux.dev, Zi Yan <ziy@nvidia.com>, lkp@intel.com,
	oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Baolin Wang <baolin.wang@linux.alibaba.com>
Subject: Re: mm/shmem.c:2223 shmem_split_large_entry() error: uninitialized
 symbol 'entry_order'.
Message-ID: <aFL7zYgdMoqNbJBS@casper.infradead.org>
References: <428fa0fe-8960-4566-9054-5bfd967c18c8@suswa.mountain>
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In-Reply-To: <428fa0fe-8960-4566-9054-5bfd967c18c8@suswa.mountain>

On Wed, Jun 18, 2025 at 08:42:17PM +0300, Dan Carpenter wrote:
> smatch warnings:
> mm/shmem.c:2223 shmem_split_large_entry() error: uninitialized symbol 'entry_order'.

...

> 12885cbe88ddf6 Baolin Wang 2024-08-12  2169  		if (!xa_is_value(old) || swp_to_radix_entry(swap) != old) {
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2170  			xas_set_err(&xas, -EEXIST);
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2171  			goto unlock;
> 
> Imagine we hit this goto on the first iteration

That can happen (but if it does, we set -EEXIST in the xa_state).

> 12885cbe88ddf6 Baolin Wang 2024-08-12  2213  unlock:
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2214  		xas_unlock_irq(&xas);
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2215  
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2216  		if (!xas_nomem(&xas, gfp))
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2217  			break;
> 
> And we hit this break.

That's guaranteed.  If there's an errno in the xa_state that isn't
-ENOMEM, xas_nomem() will fail.

> 12885cbe88ddf6 Baolin Wang 2024-08-12  2218  	}
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2219  
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2220  	if (xas_error(&xas))
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2221  		return xas_error(&xas);
> 12885cbe88ddf6 Baolin Wang 2024-08-12  2222  
> d53c78fffe7ad3 Zi Yan      2025-03-14 @2223  	return entry_order;

but if this does happen, then xas_error() will be true and we'll return
-EEXIST here instead of returning entry_order.