[PATCH] st: unblock concurrent access in st_open()

[Hannes Reinecke <hare@xxxxxxx>]

st_open() is taking a global mutex 'st_mutex' to protect
against concurrent calls to st_open(). However, as
st_open() might take quite some time before returning,
_any_ open to _any_ st device will be blocked during
that time.

Seeing that all critical sections are already protected
by individual spinlocks 'st_mutex' doesn't serve any
purpose and can be removed, unblocking concurrent
accesses.

Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
Cc: James Bottomley <jbottomley@xxxxxxxxxxxxx>
Cc: Kai Mäkisara <Kai.Makisara@xxxxxxxxxxx>
Cc: Lee Duncan <lduncan@xxxxxxxx>
---
 drivers/scsi/st.c |    8 ++------
 1 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index e41998c..c6c172e 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -74,7 +74,6 @@ static const char *verstr = "20101219";
 #include "st_options.h"
 #include "st.h"
 
-static DEFINE_MUTEX(st_mutex);
 static int buffer_kbs;
 static int max_sg_segs;
 static int try_direct_io = TRY_DIRECT_IO;
@@ -1188,7 +1187,6 @@ static int st_open(struct inode *inode, struct file *filp)
 	int dev = TAPE_NR(inode);
 	char *name;
 
-	mutex_lock(&st_mutex);
 	/*
 	 * We really want to do nonseekable_open(inode, filp); here, but some
 	 * versions of tar incorrectly call lseek on tapes and bail out if that
@@ -1197,7 +1195,6 @@ static int st_open(struct inode *inode, struct file *filp)
 	filp->f_mode &= ~(FMODE_PREAD | FMODE_PWRITE);
 
 	if (!(STp = scsi_tape_get(dev))) {
-		mutex_unlock(&st_mutex);
 		return -ENXIO;
 	}
 
@@ -1208,7 +1205,6 @@ static int st_open(struct inode *inode, struct file *filp)
 	if (STp->in_use) {
 		write_unlock(&st_dev_arr_lock);
 		scsi_tape_put(STp);
-		mutex_unlock(&st_mutex);
 		DEB( printk(ST_DEB_MSG "%s: Device already in use.\n", name); )
 		return (-EBUSY);
 	}
@@ -1262,16 +1258,16 @@ static int st_open(struct inode *inode, struct file *filp)
 			retval = (-EIO);
 		goto err_out;
 	}
-	mutex_unlock(&st_mutex);
 	return 0;
 
  err_out:
 	normalize_buffer(STp->buffer);
+	write_lock(&st_dev_arr_lock);
 	STp->in_use = 0;
+	write_unlock(&st_dev_arr_lock);
 	scsi_tape_put(STp);
 	if (resumed)
 		scsi_autopm_put_device(STp->device);
-	mutex_unlock(&st_mutex);
 	return retval;
 
 }
-- 
1.7.4.2

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