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

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Message-Id: <A9B2CD92-C7CE-478F-B361-704D1EFE7532@lightnvm.io>
Date:   Tue, 3 Oct 2017 16:43:25 +0200
From:   Javier González <jg@...htnvm.io>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
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 3 Oct 2017, at 16.20, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
> 
> 
> 
> 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.
> 

It seems to me like a false positive, but lockdep complains on the
mentioned rw_semaphore held by pblk, and on the mutex held by the
lightnvm subsystem when removing a target (dev->mlock).

[ 6037.778889] BUG: sleeping function called from invalid context at mm/vmalloc.c:1492
[ 6037.786579] in_atomic(): 1, irqs_disabled(): 0, pid: 1282, name: nvme
[ 6037.793050] 3 locks held by nvme/1282:
[ 6037.793053]  #0:  (&dev->mlock){+.+.+.}, at: [<ffffffff8ddff395>] nvm_ctl_ioctl+0x3c5/0x6a0
[ 6037.793075]  #1:  (pblk_lock){+.+.+.}, at: [<ffffffff8de0439b>] pblk_exit+0x1b/0x100
[ 6037.793092]  #2:  (&(&l_mg->free_lock)->rlock){+.+...}, at: [<ffffffff8de040ea>] pblk_line_meta_free+0x8a/0x130

Any ideas?

Thanks,
Javier




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