scsi/sd: remove big kernel lock

Every user of the BKL in the sd driver is the
result of the pushdown from the block layer
into the open/close/ioctl functions.

The only place that used to rely on the BKL is
the sdkp->openers variable, which gets converted
into an atomic_t.

Nothing else seems to rely on the BKL, since the
functions do not touch global data without holding
another lock, and the open/close functions are
still protected from concurrent execution using
the bdev->bd_mutex.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: linux-scsi@vger.kernel.org
Cc: "James E.J. Bottomley" <James.Bottomley@suse.de>
Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 01680c7c850728503bea1bf41f6658068f0f34cd..fc5d69a84af5ff66ca39fbed2e1496b3b6453f28 100644 (file)
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -783,6 +783,8 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
  *     or from within the kernel (e.g. as a result of a mount(1) ).
  *     In the latter case @inode and @filp carry an abridged amount
  *     of information as noted above.
+ *
+ *     Locking: called with bdev->bd_mutex held.
  **/
 static int sd_open(struct block_device *bdev, fmode_t mode)
 {
@@ -795,7 +797,6 @@ static int sd_open(struct block_device *bdev, fmode_t mode)
 
        SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_open\n"));
 
-       lock_kernel();
        sdev = sdkp->device;
 
        /*
@@ -834,17 +835,15 @@ static int sd_open(struct block_device *bdev, fmode_t mode)
        if (!scsi_device_online(sdev))
                goto error_out;
 
-       if (!sdkp->openers++ && sdev->removable) {
+       if ((atomic_inc_return(&sdkp->openers) == 1) && sdev->removable) {
                if (scsi_block_when_processing_errors(sdev))
                        scsi_set_medium_removal(sdev, SCSI_REMOVAL_PREVENT);
        }
 
-       unlock_kernel();
        return 0;
 
 error_out:
        scsi_disk_put(sdkp);
-       unlock_kernel();
        return retval;  
 }
 
@@ -858,6 +857,8 @@ error_out:
  *
  *     Note: may block (uninterruptible) if error recovery is underway
  *     on this disk.
+ *
+ *     Locking: called with bdev->bd_mutex held.
  **/
 static int sd_release(struct gendisk *disk, fmode_t mode)
 {
@@ -866,8 +867,7 @@ static int sd_release(struct gendisk *disk, fmode_t mode)
 
        SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_release\n"));
 
-       lock_kernel();
-       if (!--sdkp->openers && sdev->removable) {
+       if (atomic_dec_return(&sdkp->openers) && sdev->removable) {
                if (scsi_block_when_processing_errors(sdev))
                        scsi_set_medium_removal(sdev, SCSI_REMOVAL_ALLOW);
        }
@@ -877,7 +877,6 @@ static int sd_release(struct gendisk *disk, fmode_t mode)
         * XXX is followed by a "rmmod sd_mod"?
         */
        scsi_disk_put(sdkp);
-       unlock_kernel();
        return 0;
 }
 
@@ -930,7 +929,6 @@ static int sd_ioctl(struct block_device *bdev, fmode_t mode,
        SCSI_LOG_IOCTL(1, printk("sd_ioctl: disk=%s, cmd=0x%x\n",
                                                disk->disk_name, cmd));
 
-       lock_kernel();
        /*
         * If we are in the middle of error recovery, don't let anyone
         * else try and use this device.  Also, if error recovery fails, it
@@ -960,7 +958,6 @@ static int sd_ioctl(struct block_device *bdev, fmode_t mode,
                        break;
        }
 out:
-       unlock_kernel();
        return error;
 }
 
@@ -2346,7 +2343,7 @@ static int sd_probe(struct device *dev)
        sdkp->driver = &sd_template;
        sdkp->disk = gd;
        sdkp->index = index;
-       sdkp->openers = 0;
+       atomic_set(&sdkp->openers, 0);
        sdkp->previous_state = 1;
 
        if (!sdp->request_queue->rq_timeout) {

diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
index 43d3caf268efb50a00783b647caa1b25b1e7fe56..f81a9309e6de460096139856adaf924f36e1fd64 100644 (file)
--- a/drivers/scsi/sd.h
+++ b/drivers/scsi/sd.h
@@ -47,7 +47,7 @@ struct scsi_disk {
        struct scsi_device *device;
        struct device   dev;
        struct gendisk  *disk;
-       unsigned int    openers;        /* protected by BKL for now, yuck */
+       atomic_t        openers;
        sector_t        capacity;       /* size in 512-byte sectors */
        u32             index;
        unsigned short  hw_sector_size;