dax/bus.c: use the right locking mode (read vs write) in size_show

JIRA: https://issues.redhat.com/browse/RHEL-23824

commit 2acf045
Author: Vishal Verma <vishal.l.verma@intel.com>
Date:   Tue Apr 30 11:44:26 2024 -0600

    dax/bus.c: use the right locking mode (read vs write) in size_show
    
    In size_show(), the dax_dev_rwsem only needs a read lock, but was
    acquiring a write lock.  Change it to down_read_interruptible() so it
    doesn't unnecessarily hold a write lock.
    
    Link: https://lkml.kernel.org/r/20240430-vv-dax_abi_fixes-v3-4-e3dcd755774c@intel.com
    Fixes: c05ae9d ("dax/bus.c: replace driver-core lock usage by a local rwsem")
    Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
    Reviewed-by: Dan Williams <dan.j.williams@intel.com>
    Cc: Alison Schofield <alison.schofield@intel.com>
    Cc: Dave Jiang <dave.jiang@intel.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

Author: JeffMoyer

drivers/dax/bus.c

@@ -939,11 +939,11 @@ static ssize_t size_show(struct device *dev,
 	unsigned long long size;
 	int rc;
 
-	rc = down_write_killable(&dax_dev_rwsem);
+	rc = down_read_interruptible(&dax_dev_rwsem);
 	if (rc)
 		return rc;
 	size = dev_dax_size(dev_dax);
-	up_write(&dax_dev_rwsem);
+	up_read(&dax_dev_rwsem);
 
 	return sysfs_emit(buf, "%llu\n", size);
 }