BKL: introduce CONFIG_BKL.

With all the patches we have queued in the BKL removal tree, only a
few dozen modules are left that actually rely on the BKL, and even
there are lots of low-hanging fruit. We need to decide what to do
about them, this patch illustrates one of the options:

Every user of the BKL is marked as 'depends on BKL' in Kconfig,
and the CONFIG_BKL becomes a user-visible option. If it gets
disabled, no BKL using module can be built any more and the BKL
code itself is compiled out.

The one exception is file locking, which is practically always
enabled and does a 'select BKL' instead. This effectively forces
CONFIG_BKL to be enabled until we have solved the fs/lockd
mess and can apply the patch that removes the BKL from fs/locks.c.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1b4afd2e6ca0..088eea1c2bef 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -461,6 +461,15 @@ config DEBUG_MUTEXES
          This feature allows mutex semantics violations to be detected and
          reported.
 
+config BKL
+        bool "Big Kernel Lock" if (SMP || PREEMPT)
+        default y
+        help
+          This is the traditional lock that is used in old code instead
+          of proper locking. All drivers that use the BKL should depend
+          on this symbol.
+          Say Y here unless you are working on removing the BKL.
+
 config DEBUG_LOCK_ALLOC
         bool "Lock debugging: detect incorrect freeing of live locks"
         depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT