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IB/umad: BKL is not needed for ib_umad_open()

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Remove explicit lock_kernel() calls and document why the code is safe.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Roland Dreier 2008-07-11 13:54:40 -07:00 committed by Jonathan Corbet
parent 5b2d281acb
commit feae1ef116
1 changed files with 14 additions and 6 deletions
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20
drivers/infiniband/core/user_mad.c
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@ -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 problem;
* - 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;
}