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>
diff --git a/drivers/video/mx3fb.c b/drivers/video/mx3fb.c
index b7af525..567fb94 100644
--- a/drivers/video/mx3fb.c
+++ b/drivers/video/mx3fb.c
@@ -669,7 +669,7 @@
}
static int mx3fb_blank(int blank, struct fb_info *fbi);
-static int mx3fb_map_video_memory(struct fb_info *fbi);
+static int mx3fb_map_video_memory(struct fb_info *fbi, unsigned int mem_len);
static int mx3fb_unmap_video_memory(struct fb_info *fbi);
/**
@@ -742,8 +742,7 @@
if (fbi->fix.smem_start)
mx3fb_unmap_video_memory(fbi);
- fbi->fix.smem_len = mem_len;
- if (mx3fb_map_video_memory(fbi) < 0) {
+ if (mx3fb_map_video_memory(fbi, mem_len) < 0) {
mutex_unlock(&mx3_fbi->mutex);
return -ENOMEM;
}
@@ -1198,6 +1197,7 @@
/**
* mx3fb_map_video_memory() - allocates the DRAM memory for the frame buffer.
* @fbi: framebuffer information pointer
+ * @mem_len: length of mapped memory
* @return: Error code indicating success or failure
*
* This buffer is remapped into a non-cached, non-buffered, memory region to
@@ -1205,23 +1205,26 @@
* area is remapped, all virtual memory access to the video memory should occur
* at the new region.
*/
-static int mx3fb_map_video_memory(struct fb_info *fbi)
+static int mx3fb_map_video_memory(struct fb_info *fbi, unsigned int mem_len)
{
int retval = 0;
dma_addr_t addr;
fbi->screen_base = dma_alloc_writecombine(fbi->device,
- fbi->fix.smem_len,
+ mem_len,
&addr, GFP_DMA);
if (!fbi->screen_base) {
dev_err(fbi->device, "Cannot allocate %u bytes framebuffer memory\n",
- fbi->fix.smem_len);
+ mem_len);
retval = -EBUSY;
goto err0;
}
+ mutex_lock(&fbi->mm_lock);
fbi->fix.smem_start = addr;
+ fbi->fix.smem_len = mem_len;
+ mutex_unlock(&fbi->mm_lock);
dev_dbg(fbi->device, "allocated fb @ p=0x%08x, v=0x%p, size=%d.\n",
(uint32_t) fbi->fix.smem_start, fbi->screen_base, fbi->fix.smem_len);
@@ -1251,8 +1254,10 @@
fbi->screen_base, fbi->fix.smem_start);
fbi->screen_base = 0;
+ mutex_lock(&fbi->mm_lock);
fbi->fix.smem_start = 0;
fbi->fix.smem_len = 0;
+ mutex_unlock(&fbi->mm_lock);
return 0;
}