From: John Garry <john.garry@huawei.com>
To: Bart Van Assche <bvanassche@acm.org>,
"Martin K . Petersen" <martin.petersen@oracle.com>
Cc: <linux-scsi@vger.kernel.org>, Christoph Hellwig <hch@lst.de>,
Ming Lei <ming.lei@redhat.com>, Hannes Reinecke <hare@suse.de>,
Mike Christie <michael.christie@oracle.com>,
Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
"James E.J. Bottomley" <jejb@linux.ibm.com>
Subject: Re: [PATCH v4 3/4] scsi: core: Introduce a new list for SCSI proc directory entries
Date: Wed, 14 Sep 2022 10:43:51 +0100 [thread overview]
Message-ID: <33c751b4-9c6d-ac2c-d394-86ae0de3af0d@huawei.com> (raw)
In-Reply-To: <20220913195716.3966875-4-bvanassche@acm.org>
On 13/09/2022 20:57, 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:
>
> $ 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(-)
>
> 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);
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
> + 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--;
I don't see why we decrement e->present and then free e
> + 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;
>
>
> .
next prev parent reply other threads:[~2022-09-14 9:44 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-13 19:57 [PATCH v4 0/4] Prepare for constifying SCSI host templates Bart Van Assche
2022-09-13 19:57 ` [PATCH v4 1/4] scsi: esas2r: Initialize two host template members implicitly Bart Van Assche
2022-09-14 9:05 ` John Garry
2022-09-13 19:57 ` [PATCH v4 2/4] scsi: esas2r: Introduce scsi_template_proc_dir() Bart Van Assche
2022-09-14 9:06 ` John Garry
2022-09-14 16:43 ` Bart Van Assche
2022-09-14 16:53 ` John Garry
2022-09-13 19:57 ` [PATCH v4 3/4] scsi: core: Introduce a new list for SCSI proc directory entries Bart Van Assche
2022-09-14 9:43 ` John Garry [this message]
2022-09-14 16:52 ` Bart Van Assche
2022-09-13 19:57 ` [PATCH v4 4/4] scsi: core: Rework the code for dropping the LLD module reference Bart Van Assche
2022-09-14 9:52 ` John Garry
2022-09-14 17:54 ` Bart Van Assche
2022-09-14 9:21 ` [PATCH v4 0/4] Prepare for constifying SCSI host templates John Garry
2022-09-14 17:06 ` Bart Van Assche
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