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Subject[PATCH for bkl-removal] IB/umad: BKL is not needed for ib_umad_open()
Date
Remove explicit lock_kernel() calls and document why the code is safe.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
---
Hi Jon, more BKL removal for your tree. Should be ready for 2.6.27.
diff --git a/drivers/infiniband/core/user_mad.c b/drivers/infiniband/core/user_mad.c
index 260b3df..d31e5bb 100644
--- a/drivers/infiniband/core/user_mad.c
+++ b/drivers/infiniband/core/user_mad.c
@@ -47,7 +47,6 @@
#include <linux/kref.h>
#include <linux/compat.h>
#include <linux/semaphore.h>
-#include <linux/smp_lock.h>

#include <asm/uaccess.h>

@@ -778,23 +777,33 @@ static long ib_umad_compat_ioctl(struct file *filp, unsigned int cmd,
}
#endif

+/*
+ * ib_umad_open() does not need the BKL:
+ *
+ * - umad_port[] accesses are protected by port_lock, the
+ * ib_umad_port structures are properly reference counted, and
+ * everything else is purely local to the file being created, so
+ * races against other open calls are not a proble;
+ * - the ioctl method does not affect any global state outside of the
+ * file structure being operated on;
+ * - the port is added to umad_port[] as the last part of module
+ * initialization so the open method will either immediately run
+ * -ENXIO, or all required initialization will be done.
+ */
static int ib_umad_open(struct inode *inode, struct file *filp)
{
struct ib_umad_port *port;
struct ib_umad_file *file;
int ret = 0;

- lock_kernel();
spin_lock(&port_lock);
port = umad_port[iminor(inode) - IB_UMAD_MINOR_BASE];
if (port)
kref_get(&port->umad_dev->ref);
spin_unlock(&port_lock);

- if (!port) {
- unlock_kernel();
+ if (!port)
return -ENXIO;
- }

mutex_lock(&port->file_mutex);

@@ -823,7 +832,6 @@ static int ib_umad_open(struct inode *inode, struct file *filp)

out:
mutex_unlock(&port->file_mutex);
- unlock_kernel();
return ret;
}


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