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Date: Wed, 12 Nov 2025 16:38:55 +0100
From: Christoph Hellwig <hch@lst.de>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@gentwo.org>,
	David Rientjes <rientjes@google.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Harry Yoo <harry.yoo@oracle.com>,
	Eric Biggers <ebiggers@kernel.org>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/7] mempool: fix a wakeup race when sleeping for
 elements
Message-ID: <20251112153855.GA7209@lst.de>
References: <20251111135300.752962-1-hch@lst.de> <20251111135300.752962-7-hch@lst.de> <dec19492-bc23-49a0-a2b0-1cd8b5c7726e@suse.cz>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Wed, Nov 12, 2025 at 11:53:39AM +0100, Vlastimil Babka wrote:
> > +alloc:
> >  	element = remove_element(pool);
> >  	spin_unlock_irqrestore(&pool->lock, flags);
> >  
> > @@ -406,13 +407,17 @@ static void *mempool_alloc_from_pool(struct mempool *pool, gfp_t gfp_mask)
> >  		DEFINE_WAIT(wait);
> >  
> >  		prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
> > +		if (pool->curr_nr) {
> > +			finish_wait(&pool->wait, &wait);
> > +			goto alloc;
> > +		}
> >  		spin_unlock_irqrestore(&pool->lock, flags);
> I think the race already cannot exist, thanks to the pool->lock being
> unlocked after prepare_to_wait()?
> The freeing path can't bump pool->curr_nr without the lock, so the condition
> you added can't even be true, no?

You're right, I'll drop this again.