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From:   "Dilger, Andreas" <andreas.dilger@intel.com>
To:     NeilBrown <neilb@suse.com>
CC:     "Drokin, Oleg" <oleg.drokin@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        James Simmons <jsimmons@infradead.org>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
        Lustre Development List <lustre-devel@lists.lustre.org>,
        "Yong, Fan" <fan.yong@intel.com>
Subject: Re: [PATCH 14/17] staging: lustre: change sai_thread to sai_task.
Thread-Topic: [PATCH 14/17] staging: lustre: change sai_thread to sai_task.
Thread-Index: AQHTsbXQSDgx/3sOlU+zYkVjojObd6PHm4mA
Date:   Fri, 9 Mar 2018 00:20:27 +0000
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 <151994708553.7628.2646121829758742627.stgit@noble>
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> On Mar 1, 2018, at 16:31, NeilBrown <neilb@suse.com> wrote:
> 
> Rather than allocating a ptlrpc_thread for the
> stat-ahead thread, just use the task_struct provided
> by kthreads directly.
> 
> As nothing ever waits for the sai_task, it must call do_exit()
> directly rather than simply return from the function.
> Also it cannot use kthread_should_stop() to know when to stop.
> 
> There is one caller which can ask it to stop so we need a simple
> signaling mechanism.  I've chosen to set ->sai_task to NULL
> when the thread should finish up.  The thread notices this and
> cleans up and exits.
> lli_sa_lock is used to avoid races between waking up the process
> and the process exiting.
> 
> Signed-off-by: NeilBrown <neilb@suse.com>

CC'd Fan Yong, who is the author for this code.

Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>

> ---
> .../staging/lustre/lustre/llite/llite_internal.h   |    2 
> drivers/staging/lustre/lustre/llite/statahead.c    |  118 +++++++++-----------
> 2 files changed, 54 insertions(+), 66 deletions(-)
> 
> diff --git a/drivers/staging/lustre/lustre/llite/llite_internal.h b/drivers/staging/lustre/lustre/llite/llite_internal.h
> index 0c2d717fd526..d46bcf71b273 100644
> --- a/drivers/staging/lustre/lustre/llite/llite_internal.h
> +++ b/drivers/staging/lustre/lustre/llite/llite_internal.h
> @@ -1070,7 +1070,7 @@ struct ll_statahead_info {
> 				sai_agl_valid:1,/* AGL is valid for the dir */
> 				sai_in_readpage:1;/* statahead in readdir() */
> 	wait_queue_head_t	sai_waitq;      /* stat-ahead wait queue */
> -	struct ptlrpc_thread    sai_thread;     /* stat-ahead thread */
> +	struct task_struct     *sai_task;       /* stat-ahead thread */
> 	struct task_struct     *sai_agl_task;   /* AGL thread */
> 	struct list_head	sai_interim_entries; /* entries which got async
> 						      * stat reply, but not
> diff --git a/drivers/staging/lustre/lustre/llite/statahead.c b/drivers/staging/lustre/lustre/llite/statahead.c
> index 39241b952bf4..155ce3cf6f60 100644
> --- a/drivers/staging/lustre/lustre/llite/statahead.c
> +++ b/drivers/staging/lustre/lustre/llite/statahead.c
> @@ -267,7 +267,7 @@ sa_kill(struct ll_statahead_info *sai, struct sa_entry *entry)
> 
> /* called by scanner after use, sa_entry will be killed */
> static void
> -sa_put(struct ll_statahead_info *sai, struct sa_entry *entry)
> +sa_put(struct ll_statahead_info *sai, struct sa_entry *entry, struct ll_inode_info *lli)
> {
> 	struct sa_entry *tmp, *next;
> 
> @@ -295,7 +295,11 @@ sa_put(struct ll_statahead_info *sai, struct sa_entry *entry)
> 		sa_kill(sai, tmp);
> 	}
> 
> -	wake_up(&sai->sai_thread.t_ctl_waitq);
> +	spin_lock(&lli->lli_sa_lock);
> +	if (sai->sai_task)
> +		wake_up_process(sai->sai_task);
> +	spin_unlock(&lli->lli_sa_lock);
> +
> }
> 
> /*
> @@ -403,7 +407,6 @@ static struct ll_statahead_info *ll_sai_alloc(struct dentry *dentry)
> 	sai->sai_max = LL_SA_RPC_MIN;
> 	sai->sai_index = 1;
> 	init_waitqueue_head(&sai->sai_waitq);
> -	init_waitqueue_head(&sai->sai_thread.t_ctl_waitq);
> 
> 	INIT_LIST_HEAD(&sai->sai_interim_entries);
> 	INIT_LIST_HEAD(&sai->sai_entries);
> @@ -465,7 +468,7 @@ static void ll_sai_put(struct ll_statahead_info *sai)
> 		lli->lli_sai = NULL;
> 		spin_unlock(&lli->lli_sa_lock);
> 
> -		LASSERT(thread_is_stopped(&sai->sai_thread));
> +		LASSERT(sai->sai_task == NULL);
> 		LASSERT(sai->sai_agl_task == NULL);
> 		LASSERT(sai->sai_sent == sai->sai_replied);
> 		LASSERT(!sa_has_callback(sai));
> @@ -646,7 +649,6 @@ static int ll_statahead_interpret(struct ptlrpc_request *req,
> 	struct ll_inode_info     *lli = ll_i2info(dir);
> 	struct ll_statahead_info *sai = lli->lli_sai;
> 	struct sa_entry *entry = (struct sa_entry *)minfo->mi_cbdata;
> -	wait_queue_head_t *waitq = NULL;
> 	__u64 handle = 0;
> 
> 	if (it_disposition(it, DISP_LOOKUP_NEG))
> @@ -657,7 +659,6 @@ static int ll_statahead_interpret(struct ptlrpc_request *req,
> 	 * sai should be always valid, no need to refcount
> 	 */
> 	LASSERT(sai);
> -	LASSERT(!thread_is_stopped(&sai->sai_thread));
> 	LASSERT(entry);
> 
> 	CDEBUG(D_READA, "sa_entry %.*s rc %d\n",
> @@ -681,8 +682,9 @@ static int ll_statahead_interpret(struct ptlrpc_request *req,
> 	spin_lock(&lli->lli_sa_lock);
> 	if (rc) {
> 		if (__sa_make_ready(sai, entry, rc))
> -			waitq = &sai->sai_waitq;
> +			wake_up(&sai->sai_waitq);
> 	} else {
> +		int first = 0;
> 		entry->se_minfo = minfo;
> 		entry->se_req = ptlrpc_request_addref(req);
> 		/*
> @@ -693,14 +695,15 @@ static int ll_statahead_interpret(struct ptlrpc_request *req,
> 		 */
> 		entry->se_handle = handle;
> 		if (!sa_has_callback(sai))
> -			waitq = &sai->sai_thread.t_ctl_waitq;
> +			first = 1;
> 
> 		list_add_tail(&entry->se_list, &sai->sai_interim_entries);
> +
> +		if (first && sai->sai_task)
> +			wake_up_process(sai->sai_task);
> 	}
> 	sai->sai_replied++;
> 
> -	if (waitq)
> -		wake_up(waitq);
> 	spin_unlock(&lli->lli_sa_lock);
> 
> 	return rc;
> @@ -942,17 +945,13 @@ static int ll_statahead_thread(void *arg)
> 	struct inode	     *dir    = d_inode(parent);
> 	struct ll_inode_info     *lli   = ll_i2info(dir);
> 	struct ll_sb_info	*sbi    = ll_i2sbi(dir);
> -	struct ll_statahead_info *sai;
> -	struct ptlrpc_thread *sa_thread;
> +	struct ll_statahead_info *sai = lli->lli_sai;
> 	struct page	      *page = NULL;
> 	__u64		     pos    = 0;
> 	int		       first  = 0;
> 	int		       rc     = 0;
> 	struct md_op_data *op_data;
> 
> -	sai = ll_sai_get(dir);
> -	sa_thread = &sai->sai_thread;
> -	sa_thread->t_pid = current_pid();
> 	CDEBUG(D_READA, "statahead thread starting: sai %p, parent %pd\n",
> 	       sai, parent);
> 
> @@ -965,21 +964,7 @@ static int ll_statahead_thread(void *arg)
> 
> 	op_data->op_max_pages = ll_i2sbi(dir)->ll_md_brw_pages;
> 
> -	if (sbi->ll_flags & LL_SBI_AGL_ENABLED)
> -		ll_start_agl(parent, sai);
> -
> -	atomic_inc(&sbi->ll_sa_total);
> -	spin_lock(&lli->lli_sa_lock);
> -	if (thread_is_init(sa_thread))
> -		/* If someone else has changed the thread state
> -		 * (e.g. already changed to SVC_STOPPING), we can't just
> -		 * blindly overwrite that setting.
> -		 */
> -		thread_set_flags(sa_thread, SVC_RUNNING);
> -	spin_unlock(&lli->lli_sa_lock);
> -	wake_up(&sa_thread->t_ctl_waitq);
> -
> -	while (pos != MDS_DIR_END_OFF && thread_is_running(sa_thread)) {
> +	while (pos != MDS_DIR_END_OFF && sai->sai_task) {
> 		struct lu_dirpage *dp;
> 		struct lu_dirent  *ent;
> 
> @@ -996,7 +981,7 @@ static int ll_statahead_thread(void *arg)
> 
> 		dp = page_address(page);
> 		for (ent = lu_dirent_start(dp);
> -		     ent && thread_is_running(sa_thread) && !sa_low_hit(sai);
> +		     ent && sai->sai_task && !sa_low_hit(sai);
> 		     ent = lu_dirent_next(ent)) {
> 			struct lu_fid fid;
> 			__u64 hash;
> @@ -1046,13 +1031,7 @@ static int ll_statahead_thread(void *arg)
> 
> 			fid_le_to_cpu(&fid, &ent->lde_fid);
> 
> -			/* wait for spare statahead window */
> 			do {
> -				wait_event_idle(sa_thread->t_ctl_waitq,
> -						!sa_sent_full(sai) ||
> -						sa_has_callback(sai) ||
> -						!list_empty(&sai->sai_agls) ||
> -						!thread_is_running(sa_thread));
> 				sa_handle_callback(sai);
> 
> 				spin_lock(&lli->lli_agl_lock);
> @@ -1072,8 +1051,16 @@ static int ll_statahead_thread(void *arg)
> 					spin_lock(&lli->lli_agl_lock);
> 				}
> 				spin_unlock(&lli->lli_agl_lock);
> -			} while (sa_sent_full(sai) &&
> -				 thread_is_running(sa_thread));
> +
> +				set_current_state(TASK_IDLE);
> +				if (sa_sent_full(sai) &&
> +				    !sa_has_callback(sai) &&
> +				    agl_list_empty(sai) &&
> +				    sai->sai_task)
> +					/* wait for spare statahead window */
> +					schedule();
> +				__set_current_state(TASK_RUNNING);
> +			} while (sa_sent_full(sai) && sai->sai_task);
> 
> 			sa_statahead(parent, name, namelen, &fid);
> 		}
> @@ -1096,7 +1083,7 @@ static int ll_statahead_thread(void *arg)
> 
> 	if (rc < 0) {
> 		spin_lock(&lli->lli_sa_lock);
> -		thread_set_flags(sa_thread, SVC_STOPPING);
> +		sai->sai_task = NULL;
> 		lli->lli_sa_enabled = 0;
> 		spin_unlock(&lli->lli_sa_lock);
> 	}
> @@ -1105,12 +1092,14 @@ static int ll_statahead_thread(void *arg)
> 	 * statahead is finished, but statahead entries need to be cached, wait
> 	 * for file release to stop me.
> 	 */
> -	while (thread_is_running(sa_thread)) {
> -		wait_event_idle(sa_thread->t_ctl_waitq,
> -				sa_has_callback(sai) ||
> -				!thread_is_running(sa_thread));
> -
> +	while (sai->sai_task) {
> 		sa_handle_callback(sai);
> +
> +		set_current_state(TASK_IDLE);
> +		if (!sa_has_callback(sai) &&
> +		    sai->sai_task)
> +			schedule();
> +		__set_current_state(TASK_RUNNING);
> 	}
> out:
> 	if (sai->sai_agl_task) {
> @@ -1126,26 +1115,23 @@ static int ll_statahead_thread(void *arg)
> 	 */
> 	while (sai->sai_sent != sai->sai_replied) {
> 		/* in case we're not woken up, timeout wait */
> -		wait_event_idle_timeout(sa_thread->t_ctl_waitq,
> -					sai->sai_sent == sai->sai_replied,
> -					HZ>>3);
> +		schedule_timeout_idle(HZ>>3);
> 	}
> 
> 	/* release resources held by statahead RPCs */
> 	sa_handle_callback(sai);
> 
> -	spin_lock(&lli->lli_sa_lock);
> -	thread_set_flags(sa_thread, SVC_STOPPED);
> -	spin_unlock(&lli->lli_sa_lock);
> -
> 	CDEBUG(D_READA, "statahead thread stopped: sai %p, parent %pd\n",
> 	       sai, parent);
> 
> +	spin_lock(&lli->lli_sa_lock);
> +	sai->sai_task = NULL;
> +	spin_unlock(&lli->lli_sa_lock);
> +
> 	wake_up(&sai->sai_waitq);
> -	wake_up(&sa_thread->t_ctl_waitq);
> 	ll_sai_put(sai);
> 
> -	return rc;
> +	do_exit(rc);
> }
> 
> /* authorize opened dir handle @key to statahead */
> @@ -1187,13 +1173,13 @@ void ll_deauthorize_statahead(struct inode *dir, void *key)
> 	lli->lli_opendir_pid = 0;
> 	lli->lli_sa_enabled = 0;
> 	sai = lli->lli_sai;
> -	if (sai && thread_is_running(&sai->sai_thread)) {
> +	if (sai && sai->sai_task) {
> 		/*
> 		 * statahead thread may not quit yet because it needs to cache
> 		 * entries, now it's time to tell it to quit.
> 		 */
> -		thread_set_flags(&sai->sai_thread, SVC_STOPPING);
> -		wake_up(&sai->sai_thread.t_ctl_waitq);
> +		wake_up_process(sai->sai_task);
> +		sai->sai_task = NULL;
> 	}
> 	spin_unlock(&lli->lli_sa_lock);
> }
> @@ -1463,7 +1449,7 @@ static int revalidate_statahead_dentry(struct inode *dir,
> 	 */
> 	ldd = ll_d2d(*dentryp);
> 	ldd->lld_sa_generation = lli->lli_sa_generation;
> -	sa_put(sai, entry);
> +	sa_put(sai, entry, lli);
> 	return rc;
> }
> 
> @@ -1483,7 +1469,6 @@ static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
> {
> 	struct ll_inode_info *lli = ll_i2info(dir);
> 	struct ll_statahead_info *sai = NULL;
> -	struct ptlrpc_thread *thread;
> 	struct task_struct *task;
> 	struct dentry *parent = dentry->d_parent;
> 	int rc;
> @@ -1523,18 +1508,21 @@ static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
> 	CDEBUG(D_READA, "start statahead thread: [pid %d] [parent %pd]\n",
> 	       current_pid(), parent);
> 
> -	task = kthread_run(ll_statahead_thread, parent, "ll_sa_%u",
> -			   lli->lli_opendir_pid);
> -	thread = &sai->sai_thread;
> +	task = kthread_create(ll_statahead_thread, parent, "ll_sa_%u",
> +			      lli->lli_opendir_pid);
> 	if (IS_ERR(task)) {
> 		rc = PTR_ERR(task);
> 		CERROR("can't start ll_sa thread, rc : %d\n", rc);
> 		goto out;
> 	}
> 
> -	wait_event_idle(thread->t_ctl_waitq,
> -			thread_is_running(thread) || thread_is_stopped(thread));
> -	ll_sai_put(sai);
> +	if (ll_i2sbi(parent->d_inode)->ll_flags & LL_SBI_AGL_ENABLED)
> +		ll_start_agl(parent, sai);
> +
> +	atomic_inc(&ll_i2sbi(parent->d_inode)->ll_sa_total);
> +	sai->sai_task = task;
> +
> +	wake_up_process(task);
> 
> 	/*
> 	 * We don't stat-ahead for the first dirent since we are already in
> 
> 

Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Intel Corporation