On 10/8/19 9:50 AM, Douglas Gilbert wrote:
> Introduce bitops in sg_device to replace an atomic, a bool and a
> char. That char (sgdebug) had been reduced to only two states.
> Add some associated macros to make the code a little clearer.
>
> Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
> ---
> drivers/scsi/sg.c | 104 +++++++++++++++++++++++-----------------------
> 1 file changed, 53 insertions(+), 51 deletions(-)
>
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 9aa1b1030033..97ce84f0c51b 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -74,6 +74,11 @@ static char *sg_version_date = "20190606";
>
> #define SG_DEFAULT_TIMEOUT mult_frac(SG_DEFAULT_TIMEOUT_USER, HZ, USER_HZ)
>
> +/* Bit positions (flags) for sg_device::fdev_bm bitmask follow */
> +#define SG_FDEV_EXCLUDE 0 /* have fd open with O_EXCL */
> +#define SG_FDEV_DETACHING 1 /* may be unexpected device removal */
> +#define SG_FDEV_LOG_SENSE 2 /* set by ioctl(SG_SET_DEBUG) */
> +
> int sg_big_buff = SG_DEF_RESERVED_SIZE;
> /* N.B. This variable is readable and writeable via
> /proc/scsi/sg/def_reserved_size . Each time sg_open() is called a buffer
> @@ -155,14 +160,12 @@ struct sg_device { /* holds the state of each scsi generic device */
> struct scsi_device *device;
> wait_queue_head_t open_wait; /* queue open() when O_EXCL present */
> struct mutex open_rel_lock; /* held when in open() or release() */
> - int sg_tablesize; /* adapter's max scatter-gather table size */
> - u32 index; /* device index number */
> struct list_head sfds;
> rwlock_t sfd_lock; /* protect access to sfd list */
> - atomic_t detaching; /* 0->device usable, 1->device detaching */
> - bool exclude; /* 1->open(O_EXCL) succeeded and is active */
> + int sg_tablesize; /* adapter's max scatter-gather table size */
> + u32 index; /* device index number */
> int open_cnt; /* count of opens (perhaps < num(sfds) ) */
> - char sgdebug; /* 0->off, 1->sense, 9->dump dev, 10-> all devs */
> + unsigned long fdev_bm[1]; /* see SG_FDEV_* defines above */
> struct gendisk *disk;
> struct cdev * cdev; /* char_dev [sysfs: /sys/cdev/major/sg<n>] */
> struct kref d_ref;
> @@ -200,6 +203,9 @@ static void sg_device_destroy(struct kref *kref);
> #define SZ_SG_IO_HDR ((int)sizeof(struct sg_io_hdr)) /* v3 header */
> #define SZ_SG_REQ_INFO ((int)sizeof(struct sg_req_info))
>
> +#define SG_IS_DETACHING(sdp) test_bit(SG_FDEV_DETACHING, (sdp)->fdev_bm)
> +#define SG_HAVE_EXCLUDE(sdp) test_bit(SG_FDEV_EXCLUDE, (sdp)->fdev_bm)
> +
> /*
> * Kernel needs to be built with CONFIG_SCSI_LOGGING to see log messages.
> * 'depth' is a number between 1 (most severe) and 7 (most noisy, most
> @@ -273,26 +279,26 @@ sg_wait_open_event(struct sg_device *sdp, bool o_excl)
> while (sdp->open_cnt > 0) {
> mutex_unlock(&sdp->open_rel_lock);
> retval = wait_event_interruptible(sdp->open_wait,
> - (atomic_read(&sdp->detaching) ||
> + (SG_IS_DETACHING(sdp) ||
> !sdp->open_cnt));
> mutex_lock(&sdp->open_rel_lock);
>
> if (retval) /* -ERESTARTSYS */
> return retval;
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> }
> } else {
> - while (sdp->exclude) {
> + while (SG_HAVE_EXCLUDE(sdp)) {
> mutex_unlock(&sdp->open_rel_lock);
> retval = wait_event_interruptible(sdp->open_wait,
> - (atomic_read(&sdp->detaching) ||
> - !sdp->exclude));
> + (SG_IS_DETACHING(sdp) ||
> + !SG_HAVE_EXCLUDE(sdp)));
> mutex_lock(&sdp->open_rel_lock);
>
> if (retval) /* -ERESTARTSYS */
> return retval;
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> }
> }
> @@ -354,7 +360,7 @@ sg_open(struct inode *inode, struct file *filp)
> goto error_mutex_locked;
> }
> } else {
> - if (sdp->exclude) {
> + if (SG_HAVE_EXCLUDE(sdp)) {
> retval = -EBUSY;
> goto error_mutex_locked;
> }
> @@ -367,10 +373,10 @@ sg_open(struct inode *inode, struct file *filp)
>
> /* N.B. at this point we are holding the open_rel_lock */
> if (o_excl)
> - sdp->exclude = true;
> + set_bit(SG_FDEV_EXCLUDE, sdp->fdev_bm);
>
> if (sdp->open_cnt < 1) { /* no existing opens */
> - sdp->sgdebug = 0;
> + clear_bit(SG_FDEV_LOG_SENSE, sdp->fdev_bm);
> q = sdp->device->request_queue;
> sdp->sg_tablesize = queue_max_segments(q);
> }
> @@ -393,8 +399,8 @@ sg_open(struct inode *inode, struct file *filp)
> return retval;
>
> out_undo:
> - if (o_excl) {
> - sdp->exclude = false; /* undo if error */
> + if (o_excl) { /* undo if error */
> + clear_bit(SG_FDEV_EXCLUDE, sdp->fdev_bm);
> wake_up_interruptible(&sdp->open_wait);
> }
> error_mutex_locked:
> @@ -428,12 +434,10 @@ sg_release(struct inode *inode, struct file *filp)
>
> /* possibly many open()s waiting on exlude clearing, start many;
> * only open(O_EXCL)s wait on 0==open_cnt so only start one */
> - if (sdp->exclude) {
> - sdp->exclude = false;
> + if (test_and_clear_bit(SG_FDEV_EXCLUDE, sdp->fdev_bm))
> wake_up_interruptible_all(&sdp->open_wait);
> - } else if (0 == sdp->open_cnt) {
> + else if (sdp->open_cnt == 0)
> wake_up_interruptible(&sdp->open_wait);
> - }
> mutex_unlock(&sdp->open_rel_lock);
> return 0;
> }
> @@ -467,7 +471,7 @@ sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
> SG_LOG(3, sfp, "%s: write(3rd arg) count=%d\n", __func__, (int)count);
> if (!sdp)
> return -ENXIO;
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> if (!((filp->f_flags & O_NONBLOCK) ||
> scsi_block_when_processing_errors(sdp->device)))
> @@ -666,7 +670,7 @@ sg_common_write(struct sg_fd *sfp, struct sg_request *srp,
> sg_remove_request(sfp, srp);
> return k; /* probably out of space --> ENOMEM */
> }
> - if (atomic_read(&sdp->detaching)) {
> + if (SG_IS_DETACHING(sdp)) {
> if (srp->bio) {
> scsi_req_free_cmd(scsi_req(srp->rq));
> blk_put_request(srp->rq);
> @@ -831,7 +835,7 @@ sg_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
> }
> srp = sg_get_rq_mark(sfp, req_pack_id);
> if (!srp) { /* now wait on packet to arrive */
> - if (atomic_read(&sdp->detaching)) {
> + if (SG_IS_DETACHING(sdp)) {
> retval = -ENODEV;
> goto free_old_hdr;
> }
> @@ -840,9 +844,9 @@ sg_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
> goto free_old_hdr;
> }
> retval = wait_event_interruptible(sfp->read_wait,
> - (atomic_read(&sdp->detaching) ||
> + (SG_IS_DETACHING(sdp) ||
> (srp = sg_get_rq_mark(sfp, req_pack_id))));
> - if (atomic_read(&sdp->detaching)) {
> + if (SG_IS_DETACHING(sdp)) {
> retval = -ENODEV;
> goto free_old_hdr;
> }
> @@ -997,7 +1001,7 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
>
> switch (cmd_in) {
> case SG_IO:
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> if (!scsi_block_when_processing_errors(sdp->device))
> return -ENXIO;
> @@ -1008,8 +1012,8 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
> if (result < 0)
> return result;
> result = wait_event_interruptible(sfp->read_wait,
> - (srp_done(sfp, srp) || atomic_read(&sdp->detaching)));
> - if (atomic_read(&sdp->detaching))
> + (srp_done(sfp, srp) || SG_IS_DETACHING(sdp)));
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> write_lock_irq(&sfp->rq_list_lock);
> if (srp->done) {
> @@ -1052,7 +1056,7 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
> else {
> sg_scsi_id_t __user *sg_idp = p;
>
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> __put_user((int) sdp->device->host->host_no,
> &sg_idp->host_no);
> @@ -1176,18 +1180,18 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
> return result;
> }
> case SG_EMULATED_HOST:
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> return put_user(sdp->device->host->hostt->emulated, ip);
> case SCSI_IOCTL_SEND_COMMAND:
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> return sg_scsi_ioctl(sdp->device->request_queue, NULL, filp->f_mode, p);
> case SG_SET_DEBUG:
> result = get_user(val, ip);
> if (result)
> return result;
> - sdp->sgdebug = (char) val;
> + assign_bit(SG_FDEV_LOG_SENSE, sdp->fdev_bm, val);
> return 0;
> case BLKSECTGET:
> return put_user(max_sectors_bytes(sdp->device->request_queue),
> @@ -1208,7 +1212,7 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
> case SCSI_IOCTL_PROBE_HOST:
> case SG_GET_TRANSFORM:
> case SG_SCSI_RESET:
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> return -ENODEV;
> break;
> default:
> @@ -1271,7 +1275,7 @@ sg_poll(struct file *filp, poll_table * wait)
> }
> read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
>
> - if (sfp->parentdp && atomic_read(&sfp->parentdp->detaching)) {
> + if (sfp->parentdp && SG_IS_DETACHING(sfp->parentdp)) {
> p_res |= EPOLLHUP;
> } else if (!sfp->cmd_q) {
> if (count == 0)
> @@ -1419,7 +1423,7 @@ sg_rq_end_io(struct request *rq, blk_status_t status)
> return;
>
> sdp = sfp->parentdp;
> - if (unlikely(atomic_read(&sdp->detaching)))
> + if (unlikely(SG_IS_DETACHING(sdp)))
> pr_info("%s: device detaching\n", __func__);
>
> sense = req->sense;
> @@ -1440,9 +1444,9 @@ sg_rq_end_io(struct request *rq, blk_status_t status)
> srp->header.msg_status = msg_byte(result);
> srp->header.host_status = host_byte(result);
> srp->header.driver_status = driver_byte(result);
> - if ((sdp->sgdebug > 0) &&
> - ((CHECK_CONDITION == srp->header.masked_status) ||
> - (COMMAND_TERMINATED == srp->header.masked_status)))
> + if (test_bit(SG_FDEV_LOG_SENSE, sdp->fdev_bm) &&
> + (srp->header.masked_status == CHECK_CONDITION ||
> + srp->header.masked_status == COMMAND_TERMINATED))
> __scsi_print_sense(sdp->device, __func__, sense,
> SCSI_SENSE_BUFFERSIZE);
>
> @@ -1557,7 +1561,7 @@ sg_alloc(struct gendisk *disk, struct scsi_device *scsidp)
> mutex_init(&sdp->open_rel_lock);
> INIT_LIST_HEAD(&sdp->sfds);
> init_waitqueue_head(&sdp->open_wait);
> - atomic_set(&sdp->detaching, 0);
> + clear_bit(SG_FDEV_DETACHING, sdp->fdev_bm);
> rwlock_init(&sdp->sfd_lock);
> sdp->sg_tablesize = queue_max_segments(q);
> sdp->index = k;
> @@ -1682,13 +1686,11 @@ sg_remove_device(struct device *cl_dev, struct class_interface *cl_intf)
> struct sg_device *sdp = dev_get_drvdata(cl_dev);
> unsigned long iflags;
> struct sg_fd *sfp;
> - int val;
>
> if (!sdp)
> return;
> - /* want sdp->detaching non-zero as soon as possible */
> - val = atomic_inc_return(&sdp->detaching);
> - if (val > 1)
> + /* set this flag as soon as possible as it could be a surprise */
> + if (test_and_set_bit(SG_FDEV_DETACHING, sdp->fdev_bm))
> return; /* only want to do following once per device */
>
> SCSI_LOG_TIMEOUT(3, sdev_printk(KERN_INFO, sdp->device,
> @@ -2218,7 +2220,7 @@ sg_add_sfp(struct sg_device *sdp)
> sfp->keep_orphan = SG_DEF_KEEP_ORPHAN;
> sfp->parentdp = sdp;
> write_lock_irqsave(&sdp->sfd_lock, iflags);
> - if (atomic_read(&sdp->detaching)) {
> + if (SG_IS_DETACHING(sdp)) {
> write_unlock_irqrestore(&sdp->sfd_lock, iflags);
> kfree(sfp);
> return ERR_PTR(-ENODEV);
> @@ -2315,8 +2317,8 @@ sg_get_dev(int dev)
> sdp = sg_lookup_dev(dev);
> if (!sdp)
> sdp = ERR_PTR(-ENXIO);
> - else if (atomic_read(&sdp->detaching)) {
> - /* If sdp->detaching, then the refcount may already be 0, in
> + else if (SG_IS_DETACHING(sdp)) {
> + /* If detaching, then the refcount may already be 0, in
> * which case it would be a bug to do kref_get().
> */
> sdp = ERR_PTR(-ENODEV);
> @@ -2530,8 +2532,7 @@ sg_proc_seq_show_dev(struct seq_file *s, void *v)
>
> read_lock_irqsave(&sg_index_lock, iflags);
> sdp = it ? sg_lookup_dev(it->index) : NULL;
> - if ((NULL == sdp) || (NULL == sdp->device) ||
> - (atomic_read(&sdp->detaching)))
> + if (!sdp || !sdp->device || SG_IS_DETACHING(sdp))
> seq_puts(s, "-1\t-1\t-1\t-1\t-1\t-1\t-1\t-1\t-1\n");
> else {
> scsidp = sdp->device;
> @@ -2558,7 +2559,7 @@ sg_proc_seq_show_devstrs(struct seq_file *s, void *v)
> read_lock_irqsave(&sg_index_lock, iflags);
> sdp = it ? sg_lookup_dev(it->index) : NULL;
> scsidp = sdp ? sdp->device : NULL;
> - if (sdp && scsidp && (!atomic_read(&sdp->detaching)))
> + if (sdp && scsidp && !SG_IS_DETACHING(sdp))
> seq_printf(s, "%8.8s\t%16.16s\t%4.4s\n",
> scsidp->vendor, scsidp->model, scsidp->rev);
> else
> @@ -2650,7 +2651,7 @@ sg_proc_seq_show_debug(struct seq_file *s, void *v)
> read_lock(&sdp->sfd_lock);
> if (!list_empty(&sdp->sfds)) {
> seq_printf(s, " >>> device=%s ", sdp->disk->disk_name);
> - if (atomic_read(&sdp->detaching))
> + if (SG_IS_DETACHING(sdp))
> seq_puts(s, "detaching pending close ");
> else if (sdp->device) {
> struct scsi_device *scsidp = sdp->device;
> @@ -2662,7 +2663,8 @@ sg_proc_seq_show_debug(struct seq_file *s, void *v)
> scsidp->host->hostt->emulated);
> }
> seq_printf(s, " sg_tablesize=%d excl=%d open_cnt=%d\n",
> - sdp->sg_tablesize, sdp->exclude, sdp->open_cnt);
> + sdp->sg_tablesize, SG_HAVE_EXCLUDE(sdp),
> + sdp->open_cnt);
> sg_proc_debug_helper(s, sdp);
> }
> read_unlock(&sdp->sfd_lock);
>
One thing to keep in mind here is that 'set_bit()' is not atomic; it
needs to be followed by a memory barrier or being replaced by
test_and_set_bit() if possible.
Please audit the code if that poses a problem.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 247165 (AG München), GF: Felix Imendörffer
