diff mbox series

[v4,3/4] scsi: core: Introduce a new list for SCSI proc directory entries

Message ID 20220913195716.3966875-4-bvanassche@acm.org
State Superseded
Headers show
Series Prepare for constifying SCSI host templates | expand

Commit Message

Bart Van Assche Sept. 13, 2022, 7:57 p.m. UTC 
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>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_priv.h |   4 +-
 drivers/scsi/scsi_proc.c | 111 +++++++++++++++++++++++++++++++++------
 include/scsi/scsi_host.h |  12 -----
 3 files changed, 96 insertions(+), 31 deletions(-)

Comments

Bart Van Assche Sept. 14, 2022, 4:52 p.m. UTC | #1 
On 9/14/22 02:43, John Garry wrote:
> On 13/09/2022 20:57, Bart Van Assche wrote:
>> +void scsi_proc_hostdir_add(const 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);
> 
> So this following scenario is safe, right?
> 
> 1. host0 calls scsi_proc_hostdir_add() but alloc here fails
> 2. host1 calls scsi_proc_hostdir_add() but alloc passes, so e->present = 1
> 3. host0 calls scsi_proc_hostdir_rm(), so e->present goes to zero and we 
> dealloc the scsi_proc_entry
> 4. host1 calls scsi_proc_hostdir_rm(), but does not find the 
> scsi_proc_entry and returns
> 
> I suppose the only problem is that we try to free the procfs dir but 
> host1 still has a procfs entry after 3
> 
> I just wonder why we can't make scsi_alloc_alloc() -> 
> scsi_proc_hostdir_add() error, i.e. return an error code in this 
> function - it would seem to make things simpler

That sounds like a good idea to me. I will look into this.

>> +    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);
>> +        e->present--;
> 
> I don't see why we decrement e->present and then free e

I will remove the code that decrements e->present again.

Thanks,

Bart.
diff mbox series

Patch

diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index f385b3f04d6e..be5d7c9b7f39 100644
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -100,8 +100,8 @@  extern void scsi_evt_thread(struct work_struct *work);
 
 /* scsi_proc.c */
 #ifdef CONFIG_SCSI_PROC_FS
-extern void scsi_proc_hostdir_add(struct scsi_host_template *);
-extern void scsi_proc_hostdir_rm(struct scsi_host_template *);
+extern void scsi_proc_hostdir_add(const struct scsi_host_template *);
+extern void scsi_proc_hostdir_rm(const struct scsi_host_template *);
 extern void scsi_proc_host_add(struct Scsi_Host *);
 extern void scsi_proc_host_rm(struct Scsi_Host *);
 extern int scsi_init_procfs(void);
diff --git a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
index 456b43097288..7dffa73d6f92 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 int		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_GPL(scsi_template_proc_dir);
 
@@ -109,34 +152,57 @@  static const struct proc_ops proc_scsi_ops = {
  * Sets sht->proc_dir to the new directory.
  */
 
-void scsi_proc_hostdir_add(struct scsi_host_template *sht)
+void scsi_proc_hostdir_add(const 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);
+		e->present--;
+		goto unlock;
+	}
+	e->sht = sht;
+	list_add_tail(&e->entry, &scsi_proc_list);
+	e = NULL;
+unlock:
 	mutex_unlock(&global_host_template_mutex);
+
+	kfree(e);
 }
 
 /**
  * scsi_proc_hostdir_rm - remove directory in /proc for a scsi host
  * @sht: owner of directory
  */
-void scsi_proc_hostdir_rm(struct scsi_host_template *sht)
+void scsi_proc_hostdir_rm(const 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);
 }
@@ -148,16 +214,21 @@  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;
+	const struct scsi_host_template *sht = shost->hostt;
+	struct scsi_proc_entry *e;
 	struct proc_dir_entry *p;
 	char name[10];
 
-	if (!sht->proc_dir)
+	if (!sht->show_info)
+		return;
+
+	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 +241,19 @@  void scsi_proc_host_add(struct Scsi_Host *shost)
  */
 void scsi_proc_host_rm(struct Scsi_Host *shost)
 {
+	const struct scsi_host_template *sht = shost->hostt;
+	struct scsi_proc_entry *e;
 	char name[10];
 
-	if (!shost->hostt->proc_dir)
+	if (!sht->show_info)
+		return;
+
+	e = scsi_lookup_proc_entry(sht);
+	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 030faca947d2..fb8184d87384 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;