linux-kernel - Re: [PATCH 2/2] percpu: fix iteration to prevent skipping over block

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Message-ID: <20170927215125.GB15129@devbig577.frc2.facebook.com>
Date:   Wed, 27 Sep 2017 14:51:25 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Dennis Zhou <dennisszhou@...il.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Luis Henriques <lhenriques@...e.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] percpu: fix iteration to prevent skipping over block

On Wed, Sep 27, 2017 at 04:35:00PM -0500, Dennis Zhou wrote:
> The iterator functions pcpu_next_md_free_region and
> pcpu_next_fit_region use the block offset to determine if they have
> checked the area in the prior iteration. However, this causes an issue
> when the block offset is greater than subsequent block contig hints. If
> within the iterator it moves to check subsequent blocks, it may fail in
> the second predicate due to the block offset not being cleared. Thus,
> this causes the allocator to skip over blocks leading to false failures
> when allocating from the reserved chunk. While this happens in the
> general case as well, it will only fail if it cannot allocate a new
> chunk.
> 
> This patch resets the block offset to 0 to pass the second predicate
> when checking subseqent blocks within the iterator function.
> 
> Signed-off-by: Dennis Zhou <dennisszhou@...il.com>
> Reported-by: Luis Henriques <lhenriques@...e.com>

Luis, can you please verify that this fixes the allocaiton failure you
were seeing?

Thanks.

-- 
tejun