linux-kernel - Re: [PATCH v2] net/9p/client.c: fix misuse of spin_lock_irqsave for p9

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Date:   Wed, 18 Jul 2018 10:19:20 +0800
From:   piaojun <piaojun@...wei.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
CC:     Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <v9fs-developer@...ts.sourceforge.net>
Subject: Re: [PATCH v2] net/9p/client.c: fix misuse of spin_lock_irqsave for
 p9_client lock

Hi Dominique,

On 2018/7/17 19:56, Dominique Martinet wrote:
> piaojun wrote on Tue, Jul 17, 2018:
>> In p9_read_work(), we use spin_lock for client->lock, but misuse
>> spin_lock_irqsave for it in p9_fid_create(). As p9_client lock won't be
>> locked in irq context, so spin_lock is enough. And that will improve the
>> performance.
> 
> (I didn't say in v1, but the commit message sounds a bit odd to me, if
> there is any other change to the patch could you please rephrase it a
> bit?)

Yes, I will rephrase it if there is any change to the patch.

> 
>> Rebased on 9p-next.
> 
> (Likewise, this should probably go below the '---' mark to not be in the
> final commit message, 9p-next does not make sense to linux as a whole)
> 

Thanks for your suggestion.

>>
>> Signed-off-by: Jun Piao <piaojun@...wei.com>
> 
> Nitpicks aside this still looks good to me, I'm not expert in locking
> but I believe the conn_cancel stuff in trans_fd is called either from
> user context or workqueue which also is process context, while the rest
> comes from user context only.
> 
> There *are* common functions called from interrupt context (I see:
> p9_tag_lookup, p9_client_cb, p9_parse_header) but luckily enough
> none of these take the lock.
> 
> I'll give this one a little bit of time for others to review before
> picking it up, just in case, but will do if no-one complains.
> 
>> ---
>>  net/9p/client.c   | 18 ++++++++----------
>>  net/9p/trans_fd.c |  7 +++----
>>  2 files changed, 11 insertions(+), 14 deletions(-)
>>
>> diff --git a/net/9p/client.c b/net/9p/client.c
>> index 30f9aee..f6897ee 100644
>> --- a/net/9p/client.c
>> +++ b/net/9p/client.c
>> @@ -275,14 +275,14 @@ static struct p9_fcall *p9_fcall_alloc(int alloc_msize)
>>  	INIT_LIST_HEAD(&req->req_list);
>>
>>  	idr_preload(GFP_NOFS);
>> -	spin_lock_irq(&c->lock);
>> +	spin_lock(&c->lock);
>>  	if (type == P9_TVERSION)
>>  		tag = idr_alloc(&c->reqs, req, P9_NOTAG, P9_NOTAG + 1,
>>  				GFP_NOWAIT);
>>  	else
>>  		tag = idr_alloc(&c->reqs, req, 0, P9_NOTAG, GFP_NOWAIT);
>>  	req->tc->tag = tag;
>> -	spin_unlock_irq(&c->lock);
>> +	spin_unlock(&c->lock);
>>  	idr_preload_end();
>>  	if (tag < 0)
>>  		goto free;
>> @@ -328,13 +328,12 @@ struct p9_req_t *p9_tag_lookup(struct p9_client *c, u16 tag)
>>   */
>>  static void p9_free_req(struct p9_client *c, struct p9_req_t *r)
>>  {
>> -	unsigned long flags;
>>  	u16 tag = r->tc->tag;
>>
>>  	p9_debug(P9_DEBUG_MUX, "clnt %p req %p tag: %d\n", c, r, tag);
>> -	spin_lock_irqsave(&c->lock, flags);
>> +	spin_lock(&c->lock);
>>  	idr_remove(&c->reqs, tag);
>> -	spin_unlock_irqrestore(&c->lock, flags);
>> +	spin_unlock(&c->lock);
>>  	kfree(r->tc);
>>  	kfree(r->rc);
>>  	kmem_cache_free(p9_req_cache, r);
>> @@ -846,10 +845,10 @@ static struct p9_fid *p9_fid_create(struct p9_client *clnt)
>>  	fid->fid = 0;
>>
>>  	idr_preload(GFP_KERNEL);
>> -	spin_lock_irq(&clnt->lock);
>> +	spin_lock(&clnt->lock);
>>  	ret = idr_alloc_u32(&clnt->fids, fid, &fid->fid, P9_NOFID - 1,
>>  			    GFP_NOWAIT);
>> -	spin_unlock_irq(&clnt->lock);
>> +	spin_unlock(&clnt->lock);
>>  	idr_preload_end();
>>
>>  	if (!ret)
>> @@ -862,13 +861,12 @@ static struct p9_fid *p9_fid_create(struct p9_client *clnt)
>>  static void p9_fid_destroy(struct p9_fid *fid)
>>  {
>>  	struct p9_client *clnt;
>> -	unsigned long flags;
>>
>>  	p9_debug(P9_DEBUG_FID, "fid %d\n", fid->fid);
>>  	clnt = fid->clnt;
>> -	spin_lock_irqsave(&clnt->lock, flags);
>> +	spin_lock(&clnt->lock);
>>  	idr_remove(&clnt->fids, fid->fid);
>> -	spin_unlock_irqrestore(&clnt->lock, flags);
>> +	spin_unlock(&clnt->lock);
>>  	kfree(fid->rdir);
>>  	kfree(fid);
>>  }
>> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
>> index bf459ee..94ef685 100644
>> --- a/net/9p/trans_fd.c
>> +++ b/net/9p/trans_fd.c
>> @@ -197,15 +197,14 @@ static void p9_mux_poll_stop(struct p9_conn *m)
>>  static void p9_conn_cancel(struct p9_conn *m, int err)
>>  {
>>  	struct p9_req_t *req, *rtmp;
>> -	unsigned long flags;
>>  	LIST_HEAD(cancel_list);
>>
>>  	p9_debug(P9_DEBUG_ERROR, "mux %p err %d\n", m, err);
>>
>> -	spin_lock_irqsave(&m->client->lock, flags);
>> +	spin_lock(&m->client->lock);
>>
>>  	if (m->err) {
>> -		spin_unlock_irqrestore(&m->client->lock, flags);
>> +		spin_unlock(&m->client->lock);
>>  		return;
>>  	}
>>
>> @@ -217,7 +216,7 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
>>  	list_for_each_entry_safe(req, rtmp, &m->unsent_req_list, req_list) {
>>  		list_move(&req->req_list, &cancel_list);
>>  	}
>> -	spin_unlock_irqrestore(&m->client->lock, flags);
>> +	spin_unlock(&m->client->lock);
>>
>>  	list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
>>  		p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req);
>> -- 
>