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SubjectRe: [PATCH] lightnvm: pblk: use vfree_atomic when freeing line metadata
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> On 3 Oct 2017, at 16.20, Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
>
>
>
> On 10/03/2017 05:11 PM, Javier González wrote:
>>> On 3 Oct 2017, at 16.07, Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
>>>
>>>
>>>
>>> On 10/03/2017 04:48 PM, Hans Holmberg wrote:
>>>> From: Hans Holmberg <hans.holmberg@cnexlabs.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@cnexlabs.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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