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, 6 insertions, 1 deletions

diff --git a/drivers/video/atafb.c b/drivers/video/atafb.c
index 018850c116c6..497ff8af03ed 100644
--- a/drivers/video/atafb.c
+++ b/drivers/video/atafb.c
@@ -2414,7 +2414,10 @@ static int atafb_get_fix(struct fb_fix_screeninfo *fix, struct fb_info *info)
         if (err)
                 return err;
         memset(fix, 0, sizeof(struct fb_fix_screeninfo));
-        return fbhw->encode_fix(fix, &par);
+        mutex_lock(&info->mm_lock);
+        err = fbhw->encode_fix(fix, &par);
+        mutex_unlock(&info->mm_lock);
+        return err;
 }
 
 static int atafb_get_var(struct fb_var_screeninfo *var, struct fb_info *info)
@@ -2743,7 +2746,9 @@ static int atafb_set_par(struct fb_info *info)
 
         /* Decode wanted screen parameters */
         fbhw->decode_var(&info->var, par);
+        mutex_lock(&info->mm_lock);
         fbhw->encode_fix(&info->fix, par);
+        mutex_unlock(&info->mm_lock);
 
         /* Set new videomode */
         ata_set_par(par);