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    Subject[PATCH for bkl-removal v2] IB/umad: BKL is not needed for ib_umad_open()
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    Date
    Remove explicit lock_kernel() calls and document why the code is safe.

    Signed-off-by: Roland Dreier <rolandd@cisco.com>
    ---
    Resending with s/proble/problem/

    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 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;
    }


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