linux-kernel - Re: [patch] ceph: checking for IS

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Date:	Tue, 26 Jan 2016 12:40:41 +0100
From:	Ilya Dryomov <idryomov@...il.com>
To:	"Yan, Zheng" <zyan@...hat.com>
Cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	Sage Weil <sage@...hat.com>,
	Ceph Development <ceph-devel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] ceph: checking for IS_ERR instead of NULL

On Tue, Jan 26, 2016 at 12:16 PM, Yan, Zheng <zyan@...hat.com> wrote:
>
>> On Jan 26, 2016, at 18:30, Ilya Dryomov <idryomov@...il.com> wrote:
>>
>> On Tue, Jan 26, 2016 at 10:24 AM, Dan Carpenter
>> <dan.carpenter@...cle.com> wrote:
>>> ceph_osdc_alloc_request() returns NULL on error, it never returns error
>>> pointers.
>>>
>>> Fixes: 5be0389dac66 ('ceph: re-send AIO write request when getting -EOLDSNAP error')
>>> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>>>
>>> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
>>> index d37efdd..a52cf9b 100644
>>> --- a/fs/ceph/file.c
>>> +++ b/fs/ceph/file.c
>>> @@ -698,8 +698,8 @@ static void ceph_aio_retry_work(struct work_struct *work)
>>>
>>>        req = ceph_osdc_alloc_request(orig_req->r_osdc, snapc, 2,
>>>                        false, GFP_NOFS);
>>> -       if (IS_ERR(req)) {
>>> -               ret = PTR_ERR(req);
>>> +       if (!req) {
>>> +               ret = -ENOMEM;
>>>                req = orig_req;
>>>                goto out;
>>>        }
>>
>> Applied, thanks Dan.
>>
>> Zheng, I have an related concern: where do you put snapc (refcount is
>> bumped a few lines above) if ceph_osdc_alloc_request() fails?  It looks
>> like it's leaked to me.
>>
>> The BUG_ON(ret == -EOLDSNAPC) also seems a bit bogus, given that ret is
>> either -ENOMEM or ceph_osdc_start_request() retval.
>
> ceph_aio_complete_req treats -EOLDSNAP distinguishingly.  Purpose of this BUG_ON is detect potential infinite loop.

Did you miss the part about the snap context?

I get the purpose of -EOLDSNAPC assert in ceph_direct_read_write(),
where you can actually get it from ceph_osdc_wait_request() - it's
a server-side error code.  Asserting it in ceph_aio_retry_work(), in
which only client helpers are called and the only two possible error
codes are -ENOMEM and -EIO doesn't make much sense to me.

Thanks,

                Ilya