Re: kmemleak reports firmware loader funnies in iwlwifi

[Catalin Marinas <catalin.marinas@arm.com>]

Dave Jones <davej@redhat.com> wrote:
> iwlagn 0000:03:00.0: loaded firmware version 8.24.2.12
> kmemleak: Freeing unknown object at 0xffffc90018070000
> Pid: 1034, comm: NetworkManager Not tainted 2.6.31-0.25.rc0.git22.fc12.x86_64
> #1
> Call Trace:
>  [<ffffffff81139f74>] delete_object+0x5b/0x13b
>  [<ffffffff8113b012>] kmemleak_free+0x5b/0xb5
>  [<ffffffff8111dc51>] vfree+0x40/0x68
>  [<ffffffff813485e6>] release_firmware+0x49/0x6c
>  [<ffffffffa021997c>] ? iwl_mac_start+0xc5c/0x106b [iwlagn]
>  [<ffffffffa0219adc>] iwl_mac_start+0xdbc/0x106b [iwlagn]
>  [<ffffffff8109df9b>] ? __module_text_address+0x25/0x85
>
>
> So it appears to be vfree'ing something that it had no knowledge of
> ever allocating.  afaict _request_firmware only vmallocs when it's
> using a firmware image built into the driver, which isn't the case
> here, so I'm not sure why we end up trying to vfree instead of kfree
> when we call release_firmware

It seems that firmware_loading_store uses vmap() to set fw->data and
it later calls vfree() on this (maybe as a short-cut to vunmap +
__free_page).

Kmemleak doesn't track vmap allocations but tracks vmalloc/vfree
calls. A solution here is to track vmap/vunmap calls (setting the
block size to 0 or adding extra checks to make sure it doesn't scan
I/O or user pages).

Another solution (my preferred one) is to annotate some of the few
places where vmap may be used with vfree. In this particular case:


diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index ddeb819..26fb808 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -179,6 +179,13 @@ static ssize_t firmware_loading_store(struct device *dev,
 				dev_err(dev, "%s: vmap() failed\n", __func__);
 				goto err;
 			}
+			/*
+			 * This block of memory is later freed using vfree.
+			 * Since kmemleak does not track vmap calls, just
+			 * inform it about this block but ignore it during
+			 * scanning.
+			 */
+			kmemleak_alloc(fw_priv->fw->data, 0, -1, GFP_KERNEL);
 			/* Pages will be freed by vfree() */
 			fw_priv->pages = NULL;
 			fw_priv->page_array_size = 0;


-- 
Catalin