linux-kernel - Re: [PATCH] lightnvm: pblk: use vfree

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Date:   Tue, 3 Oct 2017 17:20:20 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Javier González <jg@...htnvm.io>
Cc:     Hans Holmberg <hans.ml.holmberg@...tronix.com>,
        Matias Bjørling <mb@...htnvm.io>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Hans Holmberg <hans.holmberg@...xlabs.com>
Subject: Re: [PATCH] lightnvm: pblk: use vfree_atomic when freeing line
 metadata



On 10/03/2017 05:11 PM, Javier González wrote:
>> On 3 Oct 2017, at 16.07, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
>>
>>
>>
>> On 10/03/2017 04:48 PM, Hans Holmberg wrote:
>>> From: Hans Holmberg <hans.holmberg@...xlabs.com>
>>>
>>> The commit bf22e37a6413 ("mm: add vfree_atomic()") made vfree unsafe to
>>> call in atomic context (unless the call came from an interrupt) and
>>> introduced vfree_atomic that is safe to call in atomic context.
>>>
>>> So, since we're holding locks when freeing line metadata, we need to
>>> use the atomic version of vfree.
>>>
>>> Fix this by introducing an atomic variant of pblk_mfree and
>>> switching to that in pblk_line_meta_free.
>>>
>>> Signed-off-by: Hans Holmberg <hans.holmberg@...xlabs.com>
>>> ---
>>>
>>> The patch is for:
>>> https://github.com/OpenChannelSSD/linux branch for-4.15/pblk
>>>
>>> drivers/lightnvm/pblk-init.c | 3 ++-
>>> drivers/lightnvm/pblk.h      | 8 ++++++++
>>> 2 files changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
>>> index c452478..3a191a6 100644
>>> --- a/drivers/lightnvm/pblk-init.c
>>> +++ b/drivers/lightnvm/pblk-init.c
>>> @@ -396,7 +396,8 @@ static void pblk_line_meta_free(struct pblk *pblk)
>>> 	spin_lock(&l_mg->free_lock);
>>
>> What's the point in holding ->free_lock here? It seems like it could be just dropped.
>>
> 
> This lock can indeed be dropped,

So, let's do this. This would be the best way to fix this.

> but the general pblk semaphore, which
> serializes initialization and tear down cannot. This is taken on
> pblk_exit().
> 

But semaphore is not the problem here. We can sleep under semaphore, so it's fine.

> Javier
>