Re: [PATCH 0/5] pnfs-submit fix kfree under spin lock

["William A. (Andy) Adamson" <androsadamson@gmail.com>]

On Wed, Jul 21, 2010 at 3:23 AM, Benny Halevy <bhalevy@panasas.com> wro=
te:
> On Jul. 20, 2010, 20:30 +0300, "William A. (Andy) Adamson" <androsada=
mson@gmail.com> wrote:
>> Trond and Fred informed me that kfree under a spin lock is actually
>> OK. So, maybe these patches aren't needed.
>>
>> On the other hand, with these patches we don't hold the spin lock ov=
er
>> function calls which to my mind is easier to read. Also, the
>> free_layout/free_lseg layoutdriver calls may do more than call kfree=
=2E
>
> I'm all for that.
> Just document they must not block.
> If we ever see that as a requirement we can then change the caller
> to drop the spin lock before calling the free method.

You might consider the first patch which combines looking up an lseg
and allocating the pnfs_layout_type. They are really the same job, and
I think it's more clear what is going on.

-->Andy

>
> Beny
>
>>
>> At least, we should document what we expect from the
>> free_layout/free_lseg - e.g. no side affects that conflict with bein=
g
>> called under a spinlock..
>>
>> -->Andy
>>
>> On Tue, Jul 20, 2010 at 1:01 PM, =A0<andros@netapp.com> wrote:
>>>
>>> Fix kfree under spin lock
>>>
>>> Both put_lseg and put_layout are called under the inode i_lock wher=
e the
>>> last reference will end up freeing structures.
>>>
>>> I know there has been a lot of churn in this code, but free'ing und=
er the
>>> spin lock is a no-no.
>>> In this patch I refactor the layout allocation, combining it with t=
he
>>> layout segment lookup code. The new function, pnfs_get_layout_segme=
nt takes
>>> inode spin lock, and looks to see if the requested range is service=
d by an
>>> existing layout segment. If the layout has not been allocated, allo=
cate it.
>>> If a layout segement is found, reference it and give up the lock. I=
f no
>>> layout segment is found, reference the layout for the layoutget cal=
l and
>>> give up the lock.
>>>
>>> 0001-SQUASHME-pnfs-submit-alloc-layout-don-t-call-put_lay.patch
>>> 0002-SQUASHME-pnfs-submit-use-atomic_dec_and_lock-for-lay.patch
>>>
>>> Fix the put_lseg under spin lock.
>>> 0003-SQUASHME-pnfs-submit-don-t-call-put_lseg-under-spin-.patch
>>>
>>> Cleanup.
>>> 0004-SQUASHME-pnfs-submit-pnfs_release_layout-just-use-in.patch
>>> 0005-SQUASHME-pnfs-submit-fix-has_layout-compile-error.patch
>>>
>>> Tests:
>>> CONFIG_NFS_V4_1 set:
>>> Connectathon tests pass against GFS2 and pyNFS file layout servers.
>>>
>>> CONFIG_NFS_V4_1 not set:
>>> Connectathon tests pass.
>>>
>>> -->Andy
>>>
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>