linux-kernel - Re: [Kernel Bug] WARNING in mempool_alloc

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Message-ID: <6f5881df-0e0b-4278-808b-7c0cffa12a30@suse.cz>
Date: Tue, 3 Feb 2026 17:55:27 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Christoph Hellwig <hch@...radead.org>, Harry Yoo <harry.yoo@...cle.com>
Cc: Vernon Yang <vernon2gm@...il.com>, 李龙兴
 <coregee2000@...il.com>, syzkaller@...glegroups.com,
 akpm@...ux-foundation.org, cl@...two.org, rientjes@...gle.com,
 roman.gushchin@...ux.dev, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [Kernel Bug] WARNING in mempool_alloc_noprof

On 2/3/26 17:27, Christoph Hellwig wrote:
> On Tue, Feb 03, 2026 at 06:52:39PM +0900, Harry Yoo wrote:
>> Maybe the changelog could be rephrased a bit,
>> but overall LGTM, thanks!
> 
> 
> No, that does not make sense.  If mempool is used with __GFP_RECLAIM in
> the flags it won't fail, and if it isn't, GFP_NOFAIL can't work.

So that means as long as there's __GFP_RECLAIM, __GFP_NOFAIL isn't wrong,
just redundant.

> So if there is any work in mempool_alloc it's that it should warn about
> GFP_NOFAIL.  The fix is in the callers to not pass the flag, assuming
> current kernels still do this.

We could just tolerate the redundant. The code would be simpler too. But I
don't feel too strongly about it.