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 01680c7..fc5d69a 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -783,6 +783,8 @@
* 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 @@
SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp, "sd_open\n"));
- lock_kernel();
sdev = sdkp->device;
/*
@@ -834,17 +835,15 @@
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 @@
*
* 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 @@
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 @@
* XXX is followed by a "rmmod sd_mod"?
*/
scsi_disk_put(sdkp);
- unlock_kernel();
return 0;
}
@@ -930,7 +929,6 @@
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 @@
break;
}
out:
- unlock_kernel();
return error;
}
@@ -2346,7 +2343,7 @@
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) {