fbdev: add mutex for fb_mmap locking

Add a mutex to avoid a circular locking problem between the mm layer
semaphore and fbdev ioctl mutex through the fb_mmap() call.

Also, add mutex to all places where smem_start and smem_len fields change
so the mutex inside the fb_mmap() is actually used.  Changing of these
fields before calling the framebuffer_register() are not mutexed.

This is 2.6.31 material.  It removes one lockdep (fb_mmap() and
register_framebuffer()) but there is still another one (fb_release() and
register_framebuffer()).  It also cleans up handling of the smem_start and
smem_len fields used by mutexed section of the fb_mmap().

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/video/matrox/matroxfb_base.c b/drivers/video/matrox/matroxfb_base.c
index 8e7a275df50c..59c3a2e14913 100644
--- a/drivers/video/matrox/matroxfb_base.c
+++ b/drivers/video/matrox/matroxfb_base.c
@@ -724,8 +724,10 @@ static void matroxfb_update_fix(WPMINFO2)
         struct fb_fix_screeninfo *fix = &ACCESS_FBINFO(fbcon).fix;
         DBG(__func__)
 
+        mutex_lock(&ACCESS_FBINFO(fbcon).mm_lock);
         fix->smem_start = ACCESS_FBINFO(video.base) + ACCESS_FBINFO(curr.ydstorg.bytes);
         fix->smem_len = ACCESS_FBINFO(video.len_usable) - ACCESS_FBINFO(curr.ydstorg.bytes);
+        mutex_unlock(&ACCESS_FBINFO(fbcon).mm_lock);
 }
 
 static int matroxfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
@@ -2081,6 +2083,7 @@ static int matroxfb_probe(struct pci_dev* pdev, const struct pci_device_id* dumm
         spin_lock_init(&ACCESS_FBINFO(lock.accel));
         init_rwsem(&ACCESS_FBINFO(crtc2.lock));
         init_rwsem(&ACCESS_FBINFO(altout.lock));
+        mutex_init(&ACCESS_FBINFO(fbcon).mm_lock);
         ACCESS_FBINFO(irq_flags) = 0;
         init_waitqueue_head(&ACCESS_FBINFO(crtc1.vsync.wait));
         init_waitqueue_head(&ACCESS_FBINFO(crtc2.vsync.wait));