trinity: kernel warning at drivers/video/omap2/dss/manager-sysfs.c:290 manager_alpha_blending_enabled_show+0x3c/0x60()

[Russell King - ARM Linux]

Trinity found this error on OMAP4430SDP using 3.11-rc4:

WARNING: CPU: 1 PID: 3395 at /home/rmk/git/linux-rmk/drivers/video/omap2/dss/manager-sysfs.c:290 manager_alpha_blending_enabled_show+0x3c/0x60()
Modules linked in:
CPU: 1 PID: 3395 Comm: trinity-child1 Not tainted 3.11.0-rc4+ #487
Backtrace:
[<c0016ca8>] (dump_backtrace+0x0/0x110) from [<c0016e44>] (show_stack+0x18/0x1c)
 r6:c03dc0d4 r5:00000009 r4:00000000 r3:00400040
[<c0016e2c>] (show_stack+0x0/0x1c) from [<c03949ec>] (dump_stack+0x74/0x90)
[<c0394978>] (dump_stack+0x0/0x90) from [<c0037a68>] (warn_slowpath_common+0x6c/0x8c)
 r4:00000000 r3:deaef800
[<c00379fc>] (warn_slowpath_common+0x0/0x8c) from [<c0037aac>] (warn_slowpath_null+0x24/0x2c)
 r8:dd4eb718 r7:c03dc2a0 r6:dd629f70 r5:dd4eb700 r4:dd4af000
[<c0037a88>] (warn_slowpath_null+0x0/0x2c) from [<c01e4744>] (manager_alpha_blending_enabled_show+0x3c/0x60)
[<c01e4708>] (manager_alpha_blending_enabled_show+0x0/0x60) from [<c01e41c0>] (manager_attr_show+0x20/0x2c)
 r4:de090cd0
[<c01e41a0>] (manager_attr_show+0x0/0x2c) from [<c0126ee4>] (sysfs_read_file+0xc4/0x14c)
[<c0126e20>] (sysfs_read_file+0x0/0x14c) from [<c00cef2c>] (do_readv_writev+0x118/0x24c)
[<c00cee14>] (do_readv_writev+0x0/0x24c) from [<c00cf140>] (vfs_readv+0x68/0x78)
[<c00cf0d8>] (vfs_readv+0x0/0x78) from [<c00cf19c>] (SyS_readv+0x4c/0x74)
 r5:00000000 r4:dd5b7700
[<c00cf150>] (SyS_readv+0x0/0x74) from [<c0013340>] (ret_fast_syscall+0x0/0x48)

Looking at the code:

static ssize_t manager_alpha_blending_enabled_show(
                struct omap_overlay_manager *mgr, char *buf)
{
        struct omap_overlay_manager_info info;

        mgr->get_manager_info(mgr, &info);

        WARN_ON(!dss_has_feature(FEAT_ALPHA_FIXED_ZORDER));

-rw-r--r-- 1 root root 4096 Jan  1 00:01 manager0/alpha_blending_enabled
-rw-r--r-- 1 root root 4096 Jan  1 00:01 manager1/alpha_blending_enabled
-rw-r--r-- 1 root root 4096 Jan  1 00:01 manager2/alpha_blending_enabled

So, any program in userspace can open this sysfs file and on read cause
the kernel to print a warning and taint itself if there is no ZORDER
feature?  This is not good kernel programming guys.  Please audit your
other sysfs files for this bug, thanks.