console: Move userspace I/O out of console_lock to fix lockdep warning
When running certain workload on a debug kernel with lockdep turned on,
a ppc64 kvm guest could sometimes hit the following lockdep warning:
[ INFO: possible circular locking dependency detected ]
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&mm->mmap_sem);
lock(console_lock);
lock(&mm->mmap_sem);
lock(cpu_hotplug.lock);
*** DEADLOCK ***
Looking at the console code, the console_lock-->mmap_sem scenario will
only happen when reading or writing the console unicode map leading to
a page fault.
To break this circular locking dependency, all the userspace I/O
operations in consolemap.c are now moved outside of the console_lock
critical sections so that the mmap_sem won't be acquired when holding
the console_lock.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed