I stared at this code for a while and almost deleted it before
understanding crept into my slow brain.  Hopefully this makes life easier
for the next person to happen on it.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

All of the open() functions which don't need the BKL on their face may
still depend on its acquisition to serialize opens against driver
initialization.  So make those functions acquire then release the BKL to be
on the safe side.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

A number of driver functions are so obviously trivial that they do not need
the big kernel lock - at least not overtly.  It turns out that the
acquisition of the BKL in driver open() functions can perform a sort of
poor-hacker's serialization function, delaying the open operation until the
driver is certain to have completed its initialization.  Add a simple
cycle_kernel_lock() function for these cases to make it clear that there is
no need to *hold* the BKL, just to be sure that we can acquire it.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel() calls into videodev_open().  That function
itself seems OK, but one never knows about all the open() functions
provided by underlying video drivers.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add explicit lock_kernel() calls to usbdev_open()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add explicit lock_kernel() calls to mon_bin_open()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add explicit lock_kernel() calls to printer_open()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel() calls in adb_open().  The fact that
adb_release() already has them suggests this is necessary.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel() calls into maint_open().
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel() calls into capi_open()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add lock_kernel() calls to ch_open(), though the existing locking looks
adequate.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add lock_kernel() calls to adpt_open()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add explicit lock_kernel() calls to vfc_open().
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel() calls into bpp_open().  It has locking, but I'm
not convinced it won't race with ioctl().
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add explicit lock_kernel calls to phantom_open().
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Be extra-cautious and protect the remaining open() functions.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel calls into dsp56k_open().

[Stupid missing label error fixed]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel() calls into raw_open(), even though the existing
locking looks adequate.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Put explicit lock_kernel calls into tlclk_open()
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add explicit lock_kernel() calls to hwicap_open() even though the existing
locking looks adequate.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add explicit BKL to vcs_open().
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Add the BKL to spidev_open(), even though the existing locking looks
adequate.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

This documents the fact that somebody looked at the relevant open()
functions and concluded that, due to their trivial nature, no locking was
needed.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Parts of the serial code actually BUG() if we don't do this.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

usb_open() is protected by a down_read(&minor_rwsem), but I'm not sure I
trust it to protect everything including subsidiary open() functions.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

->release() already has explicit lock_kernel() calls...
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

phone_open() looks OK, but I don't trust the subsidiary drivers (and ixj in
particular).
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

This driver would appear to have no internal locking at all.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>