[PATCH v2 0/2] Prepare for constifying SCSI host templates

[PATCH v2 0/2] Prepare for constifying SCSI host templates

[Bart Van Assche]

Hi Martin,

This patch series prepares for constifying SCSI host templates by moving the
members that are not constant out of the SCSI host template. Please consider
this patch series for the next merge window.

Thanks,

Bart.

Changes compared to v1: fix the CONFIG_SCSI_PROC_FS=n build.

Bart Van Assche (2):
  scsi: esas2r: Introduce scsi_template_proc_dir()
  scsi: core: Introduce a new list for SCSI proc directory entries

 drivers/scsi/esas2r/esas2r_main.c |  18 +++--
 drivers/scsi/scsi_proc.c          | 106 ++++++++++++++++++++++++++----
 include/scsi/scsi_host.h          |  18 ++---
 3 files changed, 110 insertions(+), 32 deletions(-)

[PATCH v2 1/2] scsi: esas2r: Introduce scsi_template_proc_dir()

[Bart Van Assche]

Prepare for removing the 'proc_dir' and 'present' members from the SCSI
host template. This patch does not change any functionality.

Cc: Bradley Grove <linuxdrivers@attotech.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: John Garry <john.garry@huawei.com>
Cc: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/esas2r/esas2r_main.c | 18 +++++++++++-------
 drivers/scsi/scsi_proc.c          | 11 +++++++++++
 include/scsi/scsi_host.h          |  6 ++++++
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/esas2r/esas2r_main.c b/drivers/scsi/esas2r/esas2r_main.c
index 7a4eadad23d7..fbf7fdb3b52a 100644
--- a/drivers/scsi/esas2r/esas2r_main.c
+++ b/drivers/scsi/esas2r/esas2r_main.c
@@ -248,7 +248,6 @@ static struct scsi_host_template driver_template = {
 	.sg_tablesize			= SG_CHUNK_SIZE,
 	.cmd_per_lun			=
 		ESAS2R_DEFAULT_CMD_PER_LUN,
-	.present			= 0,
 	.emulated			= 0,
 	.proc_name			= ESAS2R_DRVR_NAME,
 	.change_queue_depth		= scsi_change_queue_depth,
@@ -637,10 +636,13 @@ static void __exit esas2r_exit(void)
 	esas2r_log(ESAS2R_LOG_INFO, "%s called", __func__);
 
 	if (esas2r_proc_major > 0) {
+		struct proc_dir_entry *proc_dir;
+
 		esas2r_log(ESAS2R_LOG_INFO, "unregister proc");
 
-		remove_proc_entry(ATTONODE_NAME,
-				  esas2r_proc_host->hostt->proc_dir);
+		proc_dir = scsi_template_proc_dir(esas2r_proc_host->hostt);
+		if (proc_dir)
+			remove_proc_entry(ATTONODE_NAME, proc_dir);
 		unregister_chrdev(esas2r_proc_major, ESAS2R_DRVR_NAME);
 
 		esas2r_proc_major = 0;
@@ -730,11 +732,13 @@ const char *esas2r_info(struct Scsi_Host *sh)
 			       esas2r_proc_major);
 
 		if (esas2r_proc_major > 0) {
-			struct proc_dir_entry *pde;
+			struct proc_dir_entry *proc_dir;
+			struct proc_dir_entry *pde = NULL;
 
-			pde = proc_create(ATTONODE_NAME, 0,
-					  sh->hostt->proc_dir,
-					  &esas2r_proc_ops);
+			proc_dir = scsi_template_proc_dir(sh->hostt);
+			if (proc_dir)
+				pde = proc_create(ATTONODE_NAME, 0, proc_dir,
+						  &esas2r_proc_ops);
 
 			if (!pde) {
 				esas2r_log_dev(ESAS2R_LOG_WARN,
diff --git a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
index 95aee1ad1383..eeb9261c93f7 100644
--- a/drivers/scsi/scsi_proc.c
+++ b/drivers/scsi/scsi_proc.c
@@ -83,6 +83,17 @@ static int proc_scsi_host_open(struct inode *inode, struct file *file)
 				4 * PAGE_SIZE);
 }
 
+/**
+ * scsi_template_proc_dir() - returns the procfs dir for a SCSI host template
+ * @sht: SCSI host template pointer.
+ */
+struct proc_dir_entry *
+scsi_template_proc_dir(const struct scsi_host_template *sht)
+{
+	return sht->proc_dir;
+}
+EXPORT_SYMBOL(scsi_template_proc_dir);
+
 static const struct proc_ops proc_scsi_ops = {
 	.proc_open	= proc_scsi_host_open,
 	.proc_release	= single_release,
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index aa7b7496c93a..c2b8427e0305 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -752,6 +752,12 @@ extern struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *, int);
 extern int __must_check scsi_add_host_with_dma(struct Scsi_Host *,
 					       struct device *,
 					       struct device *);
+#if defined(CONFIG_SCSI_PROC_FS)
+struct proc_dir_entry *
+scsi_template_proc_dir(const struct scsi_host_template *sht);
+#else
+#define scsi_template_proc_dir(sht) NULL
+#endif
 extern void scsi_scan_host(struct Scsi_Host *);
 extern void scsi_rescan_device(struct device *);
 extern void scsi_remove_host(struct Scsi_Host *);

[PATCH v2 2/2] scsi: core: Introduce a new list for SCSI proc directory entries

[Bart Van Assche]

Instead of using scsi_host_template members to track the SCSI proc
directory entries, track these entries in a list. This patch changes the
time needed for looking up the proc dir pointer from O(1) into O(n). I
think this is acceptable since the number of SCSI host adapter types per
host is usually small (less than ten).

This patch has been tested by attaching two USB storage devices to a
qemu host:

$ grep -aH . /proc/scsi/usb-storage/*
/proc/scsi/usb-storage/7:   Host scsi7: usb-storage
/proc/scsi/usb-storage/7:       Vendor: QEMU
/proc/scsi/usb-storage/7:      Product: QEMU USB HARDDRIVE
/proc/scsi/usb-storage/7:Serial Number: 1-0000:00:02.1:00.0-6
/proc/scsi/usb-storage/7:     Protocol: Transparent SCSI
/proc/scsi/usb-storage/7:    Transport: Bulk
/proc/scsi/usb-storage/7:       Quirks: SANE_SENSE
/proc/scsi/usb-storage/8:   Host scsi8: usb-storage
/proc/scsi/usb-storage/8:       Vendor: QEMU
/proc/scsi/usb-storage/8:      Product: QEMU USB HARDDRIVE
/proc/scsi/usb-storage/8:Serial Number: 1-0000:00:02.1:00.0-7
/proc/scsi/usb-storage/8:     Protocol: Transparent SCSI
/proc/scsi/usb-storage/8:    Transport: Bulk
/proc/scsi/usb-storage/8:       Quirks: SANE_SENSE

This patch prepares for constifying most SCSI host templates.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: John Garry <john.garry@huawei.com>
Cc: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_proc.c | 97 ++++++++++++++++++++++++++++++++++------
 include/scsi/scsi_host.h | 12 -----
 2 files changed, 83 insertions(+), 26 deletions(-)

diff --git a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
index eeb9261c93f7..702b78963c2e 100644
--- a/drivers/scsi/scsi_proc.c
+++ b/drivers/scsi/scsi_proc.c
@@ -43,8 +43,23 @@
 
 static struct proc_dir_entry *proc_scsi;
 
-/* Protect sht->present and sht->proc_dir */
+/* Protects scsi_proc_list */
 static DEFINE_MUTEX(global_host_template_mutex);
+static LIST_HEAD(scsi_proc_list);
+
+/**
+ * struct scsi_proc_entry - (host template, SCSI proc dir) association
+ * @entry: entry in scsi_proc_list.
+ * @sht: SCSI host template associated with the procfs directory.
+ * @proc_dir: procfs directory associated with the SCSI host template.
+ * @present: Number of SCSI hosts instantiated for @sht.
+ */
+struct scsi_proc_entry {
+	struct list_head	entry;
+	const struct scsi_host_template *sht;
+	struct proc_dir_entry	*proc_dir;
+	unsigned char		present;
+};
 
 static ssize_t proc_scsi_host_write(struct file *file, const char __user *buf,
                            size_t count, loff_t *ppos)
@@ -83,6 +98,32 @@ static int proc_scsi_host_open(struct inode *inode, struct file *file)
 				4 * PAGE_SIZE);
 }
 
+static struct scsi_proc_entry *
+__scsi_lookup_proc_entry(const struct scsi_host_template *sht)
+{
+	struct scsi_proc_entry *e;
+
+	lockdep_assert_held(&global_host_template_mutex);
+
+	list_for_each_entry(e, &scsi_proc_list, entry)
+		if (e->sht == sht)
+			return e;
+
+	return NULL;
+}
+
+static struct scsi_proc_entry *
+scsi_lookup_proc_entry(const struct scsi_host_template *sht)
+{
+	struct scsi_proc_entry *e;
+
+	mutex_lock(&global_host_template_mutex);
+	e = __scsi_lookup_proc_entry(sht);
+	mutex_unlock(&global_host_template_mutex);
+
+	return e;
+}
+
 /**
  * scsi_template_proc_dir() - returns the procfs dir for a SCSI host template
  * @sht: SCSI host template pointer.
@@ -90,7 +131,9 @@ static int proc_scsi_host_open(struct inode *inode, struct file *file)
 struct proc_dir_entry *
 scsi_template_proc_dir(const struct scsi_host_template *sht)
 {
-	return sht->proc_dir;
+	struct scsi_proc_entry *e = scsi_lookup_proc_entry(sht);
+
+	return e ? e->proc_dir : NULL;
 }
 EXPORT_SYMBOL(scsi_template_proc_dir);
 
@@ -111,17 +154,35 @@ static const struct proc_ops proc_scsi_ops = {
 
 void scsi_proc_hostdir_add(struct scsi_host_template *sht)
 {
+	struct scsi_proc_entry *e;
+
 	if (!sht->show_info)
 		return;
 
 	mutex_lock(&global_host_template_mutex);
-	if (!sht->present++) {
-		sht->proc_dir = proc_mkdir(sht->proc_name, proc_scsi);
-        	if (!sht->proc_dir)
-			printk(KERN_ERR "%s: proc_mkdir failed for %s\n",
-			       __func__, sht->proc_name);
+	e = __scsi_lookup_proc_entry(sht);
+	if (!e) {
+		e = kzalloc(sizeof(*e), GFP_KERNEL);
+		if (!e)
+			goto unlock;
+	}
+	if (e->present++) {
+		e = NULL;
+		goto unlock;
+	}
+	e->proc_dir = proc_mkdir(sht->proc_name, proc_scsi);
+	if (!e->proc_dir) {
+		printk(KERN_ERR "%s: proc_mkdir failed for %s\n", __func__,
+		       sht->proc_name);
+		goto unlock;
 	}
+	e->sht = sht;
+	list_add_tail(&e->entry, &scsi_proc_list);
+	e = NULL;
+unlock:
 	mutex_unlock(&global_host_template_mutex);
+
+	kfree(e);
 }
 
 /**
@@ -130,13 +191,17 @@ void scsi_proc_hostdir_add(struct scsi_host_template *sht)
  */
 void scsi_proc_hostdir_rm(struct scsi_host_template *sht)
 {
+	struct scsi_proc_entry *e;
+
 	if (!sht->show_info)
 		return;
 
 	mutex_lock(&global_host_template_mutex);
-	if (!--sht->present && sht->proc_dir) {
+	e = __scsi_lookup_proc_entry(sht);
+	if (e && !--e->present) {
 		remove_proc_entry(sht->proc_name, proc_scsi);
-		sht->proc_dir = NULL;
+		list_del(&e->entry);
+		kfree(e);
 	}
 	mutex_unlock(&global_host_template_mutex);
 }
@@ -149,15 +214,17 @@ void scsi_proc_hostdir_rm(struct scsi_host_template *sht)
 void scsi_proc_host_add(struct Scsi_Host *shost)
 {
 	struct scsi_host_template *sht = shost->hostt;
+	struct scsi_proc_entry *e;
 	struct proc_dir_entry *p;
 	char name[10];
 
-	if (!sht->proc_dir)
+	e = scsi_lookup_proc_entry(sht);
+	if (!e)
 		return;
 
 	sprintf(name,"%d", shost->host_no);
-	p = proc_create_data(name, S_IRUGO | S_IWUSR,
-		sht->proc_dir, &proc_scsi_ops, shost);
+	p = proc_create_data(name, S_IRUGO | S_IWUSR, e->proc_dir,
+			     &proc_scsi_ops, shost);
 	if (!p)
 		printk(KERN_ERR "%s: Failed to register host %d in"
 		       "%s\n", __func__, shost->host_no,
@@ -170,13 +237,15 @@ void scsi_proc_host_add(struct Scsi_Host *shost)
  */
 void scsi_proc_host_rm(struct Scsi_Host *shost)
 {
+	struct scsi_proc_entry *e;
 	char name[10];
 
-	if (!shost->hostt->proc_dir)
+	e = scsi_lookup_proc_entry(shost->hostt);
+	if (!e)
 		return;
 
 	sprintf(name,"%d", shost->host_no);
-	remove_proc_entry(name, shost->hostt->proc_dir);
+	remove_proc_entry(name, e->proc_dir);
 }
 /**
  * proc_print_scsidevice - return data about this host
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index c2b8427e0305..f2294d44013c 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -357,12 +357,6 @@ struct scsi_host_template {
 	 */
 	const char *proc_name;
 
-	/*
-	 * Used to store the procfs directory if a driver implements the
-	 * show_info method.
-	 */
-	struct proc_dir_entry *proc_dir;
-
 	/*
 	 * This determines if we will use a non-interrupt driven
 	 * or an interrupt driven scheme.  It is set to the maximum number
@@ -423,12 +417,6 @@ struct scsi_host_template {
 	 */
 	short cmd_per_lun;
 
-	/*
-	 * present contains counter indicating how many boards of this
-	 * type were found when we did the scan.
-	 */
-	unsigned char present;
-
 	/* If use block layer to manage tags, this is tag allocation policy */
 	int tag_alloc_policy;
 

Re: [PATCH v2 0/2] Prepare for constifying SCSI host templates

[John Garry]

On 30/08/2022 22:05, Bart Van Assche wrote:

+ Krzysztof

This is the same topic as what Krzysztof was working on in 
https://lore.kernel.org/linux-scsi/6f28acde-2177-0bc7-b06d-c704153489c0@linaro.org/

And at least we have the scsi_host_template.module issue to solve - any 
plan or progress for that?

Thanks,
John

> Hi Martin,
> 
> This patch series prepares for constifying SCSI host templates by moving the
> members that are not constant out of the SCSI host template. Please consider
> this patch series for the next merge window.
> 
> Thanks,
> 
> Bart.
> 
> Changes compared to v1: fix the CONFIG_SCSI_PROC_FS=n build.
> 
> Bart Van Assche (2):
>    scsi: esas2r: Introduce scsi_template_proc_dir()
>    scsi: core: Introduce a new list for SCSI proc directory entries
> 
>   drivers/scsi/esas2r/esas2r_main.c |  18 +++--
>   drivers/scsi/scsi_proc.c          | 106 ++++++++++++++++++++++++++----
>   include/scsi/scsi_host.h          |  18 ++---
>   3 files changed, 110 insertions(+), 32 deletions(-)
> 
> .

Re: [PATCH v2 0/2] Prepare for constifying SCSI host templates

[Krzysztof Kozlowski]

On 01/09/2022 16:23, John Garry wrote:
> On 30/08/2022 22:05, Bart Van Assche wrote:
> 
> + Krzysztof
> 
> This is the same topic as what Krzysztof was working on in 
> https://lore.kernel.org/linux-scsi/6f28acde-2177-0bc7-b06d-c704153489c0@linaro.org/
> 
> And at least we have the scsi_host_template.module issue to solve - any 
> plan or progress for that?

I won't have time to work on that anytime soon, so feel free to pickup
my patchset and rework or continue on your own.

Best regards,
Krzysztof

Re: [PATCH v2 2/2] scsi: core: Introduce a new list for SCSI proc directory entries

[Mike Christie]

On 8/30/22 4:05 PM, Bart Van Assche wrote:
> Instead of using scsi_host_template members to track the SCSI proc
> directory entries, track these entries in a list. This patch changes the
> time needed for looking up the proc dir pointer from O(1) into O(n). I
> think this is acceptable since the number of SCSI host adapter types per
> host is usually small (less than ten).
> 
> This patch has been tested by attaching two USB storage devices to a
> qemu host:
> 


>  }
> @@ -149,15 +214,17 @@ void scsi_proc_hostdir_rm(struct scsi_host_template *sht)
>  void scsi_proc_host_add(struct Scsi_Host *shost)
>  {
>  	struct scsi_host_template *sht = shost->hostt;
> +	struct scsi_proc_entry *e;
>  	struct proc_dir_entry *p;
>  	char name[10];
>  
> -	if (!sht->proc_dir)


>   */
>  void scsi_proc_host_rm(struct Scsi_Host *shost)
>  {
> +	struct scsi_proc_entry *e;
>  	char name[10];
>  
> -	if (!shost->hostt->proc_dir)


Hey Bart, Would it better to replace those two checks with a

if (!sht->show_info)
	return;

like is done in scsi_proc_hostdir_add/scsi_proc_hostdir_rm? In those
hostdir functions if show_info is not set, you will not add an entry to
scsi_proc_list. So in the above functions if that callout is not set
you know there is no entry on &scsi_proc_list and don't need to grab the
global_host_template_mutex for those cases.

I can't really test but someone did say they had 1000s of scsi_hosts for
iscsi. I'm not really sure how big a deal it is since we wouldn't be
doing a lot of work with that mutex hold, but it seems like a simple and
nice change just in case.

Re: [PATCH v2 2/2] scsi: core: Introduce a new list for SCSI proc directory entries

[Bart Van Assche]

On 9/8/22 09:03, Mike Christie wrote:
> On 8/30/22 4:05 PM, Bart Van Assche wrote:
>>   void scsi_proc_host_rm(struct Scsi_Host *shost)
>>   {
>> +	struct scsi_proc_entry *e;
>>   	char name[10];
>>   
>> -	if (!shost->hostt->proc_dir)
> 
> 
> Hey Bart, Would it better to replace those two checks with a
> 
> if (!sht->show_info)
> 	return;
> 
> like is done in scsi_proc_hostdir_add/scsi_proc_hostdir_rm? In those
> hostdir functions if show_info is not set, you will not add an entry to
> scsi_proc_list. So in the above functions if that callout is not set
> you know there is no entry on &scsi_proc_list and don't need to grab the
> global_host_template_mutex for those cases.

That sounds like an interesting idea to me.

> I can't really test but someone did say they had 1000s of scsi_hosts for
> iscsi. I'm not really sure how big a deal it is since we wouldn't be
> doing a lot of work with that mutex hold, but it seems like a simple and
> nice change just in case.

How about switching from a linked list to a hash table?

Thanks,

Bart.

Re: [PATCH v2 0/2] Prepare for constifying SCSI host templates

[Bart Van Assche]

On 9/8/22 08:04, Krzysztof Kozlowski wrote:
> On 01/09/2022 16:23, John Garry wrote:
>> On 30/08/2022 22:05, Bart Van Assche wrote:
>>
>> + Krzysztof
>>
>> This is the same topic as what Krzysztof was working on in
>> https://lore.kernel.org/linux-scsi/6f28acde-2177-0bc7-b06d-c704153489c0@linaro.org/
>>
>> And at least we have the scsi_host_template.module issue to solve - any
>> plan or progress for that?
> 
> I won't have time to work on that anytime soon, so feel free to pickup
> my patchset and rework or continue on your own.

Thanks for the feedback Krzysztof. I will keep you in Cc when I repost 
this patch series.

Bart.

Re: [PATCH v2 0/2] Prepare for constifying SCSI host templates

[Bart Van Assche]

On 9/1/22 07:23, John Garry wrote:
> And at least we have the scsi_host_template.module issue to solve - any plan or progress for that?

Hi John,

How about the following (entirely untested) patch?


Subject: [PATCH] scsi: core: Rework the code for dropping the kernel module reference

Instead of clearing the host template module pointer if the LLD kernel
module is being unloaded, set the 'drop_module_ref' SCSI device member.
This patch prepares for constifying the SCSI host template.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
  drivers/scsi/scsi_sysfs.c  | 7 +++----
  include/scsi/scsi_device.h | 1 +
  2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 5d61f58399dc..822ae60a64b9 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -454,7 +454,7 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)

  	sdev = container_of(work, struct scsi_device, ew.work);

-	mod = sdev->host->hostt->module;
+	mod = sdev->drop_module_ref ? sdev->host->hostt->module : NULL;

  	scsi_dh_release_device(sdev);

@@ -525,9 +525,8 @@ static void scsi_device_dev_release(struct device *dev)
  {
  	struct scsi_device *sdp = to_scsi_device(dev);

-	/* Set module pointer as NULL in case of module unloading */
-	if (!try_module_get(sdp->host->hostt->module))
-		sdp->host->hostt->module = NULL;
+	if (try_module_get(sdp->host->hostt->module))
+		sdp->drop_module_ref = true;

  	execute_in_process_context(scsi_device_dev_release_usercontext,
  				   &sdp->ew);
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 2493bd65351a..b03176b69056 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -214,6 +214,7 @@ struct scsi_device {
  					 * creation time */
  	unsigned ignore_media_change:1; /* Ignore MEDIA CHANGE on resume */
  	unsigned silence_suspend:1;	/* Do not print runtime PM related messages */
+	unsigned drop_module_ref:1;

  	unsigned int queue_stopped;	/* request queue is quiesced */
  	bool offline_already;		/* Device offline message logged */