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

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Message-ID: <87lgkzkywr.fsf@hermes>
Date:   Thu, 28 Sep 2017 09:31:00 +0100
From:   Luis Henriques <lhenriques@...e.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Dennis Zhou <dennisszhou@...il.com>,
        Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] percpu: fix iteration to prevent skipping over block

Tejun Heo <tj@...nel.org> writes:

> 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?

I can confirm that I'm no longer seeing the allocation failure after
applying these patches.  Feel free to add my:

Tested-by: Luis Henriques <lhenriques@...e.com>

Cheers,
-- 
Luis