fbdev: fix recursive notifier and locking when fbdev console is blanked

fbdev: fix recursive notifier and locking when fbdev console is blanked

Fix infinite recursive notifier in the fbdev layer.  This causes recursive
locking.  Dmitry Baryshkov found the problem and confirmed that the patch
fixes the bug.

After doing
# echo 1 > /sys/class/graphics/fb0/blank
I got the following in my kernel log:

=============================================
[ INFO: possible recursive locking detected ]
2.6.27-rc6-00086-gda63874-dirty #97
---------------------------------------------
echo/1564 is trying to acquire lock:
 ((fb_notifier_list).rwsem){..--}, at: [<c005a384>] __blocking_notifier_call_chain+0x38/0x6c

but task is already holding lock:
 ((fb_notifier_list).rwsem){..--}, at: [<c005a384>] __blocking_notifier_call_chain+0x38/0x6c

other info that might help us debug this:
2 locks held by echo/1564:
 #0:  (&buffer->mutex){--..}, at: [<c00ddde0>] sysfs_write_file+0x30/0x80
 #1:  ((fb_notifier_list).rwsem){..--}, at: [<c005a384>] __blocking_notifier_call_chain+0x38/0x6c

stack backtrace:
[<c0029fe4>] (dump_stack+0x0/0x14) from [<c0060ce0>] (print_deadlock_bug+0xa4/0xd0)
[<c0060c3c>] (print_deadlock_bug+0x0/0xd0) from [<c0060e54>] (check_deadlock+0x148/0x17c)
 r6:c397a1e0 r5:c397a530 r4:c04fcf98
[<c0060d0c>] (check_deadlock+0x0/0x17c) from [<c00637e8>] (validate_chain+0x3c4/0x4f0)
[<c0063424>] (validate_chain+0x0/0x4f0) from [<c0063efc>] (__lock_acquire+0x5e8/0x6b4)
[<c0063914>] (__lock_acquire+0x0/0x6b4) from [<c006402c>] (lock_acquire+0x64/0x78)
[<c0063fc8>] (lock_acquire+0x0/0x78) from [<c0316ca8>] (down_read+0x4c/0x60)
 r7:00000009 r6:ffffffff r5:c0427a40 r4:c005a384
[<c0316c5c>] (down_read+0x0/0x60) from [<c005a384>] (__blocking_notifier_call_chain+0x38/0x6c)
 r5:c0427a40 r4:c0427a74
[<c005a34c>] (__blocking_notifier_call_chain+0x0/0x6c) from [<c005a3d8>] (blocking_notifier_call_chain+0x20/0x28)
 r8:00000009 r7:c086d640 r6:c3967940 r5:00000000 r4:c38984b8
[<c005a3b8>] (blocking_notifier_call_chain+0x0/0x28) from [<c014baa0>] (fb_notifier_call_chain+0x1c/0x24)
[<c014ba84>] (fb_notifier_call_chain+0x0/0x24) from [<c014c18c>] (fb_blank+0x64/0x70)
[<c014c128>] (fb_blank+0x0/0x70) from [<c0155978>] (fbcon_blank+0x114/0x1bc)
 r5:00000001 r4:c38984b8
[<c0155864>] (fbcon_blank+0x0/0x1bc) from [<c0170ea8>] (do_blank_screen+0x1e0/0x2a0)
[<c0170cc8>] (do_blank_screen+0x0/0x2a0) from [<c0154024>] (fbcon_fb_blanked+0x74/0x94)
 r5:c3967940 r4:00000001
[<c0153fb0>] (fbcon_fb_blanked+0x0/0x94) from [<c0154228>] (fbcon_event_notify+0x100/0x12c)
 r5:fffffffe r4:c39bc194
[<c0154128>] (fbcon_event_notify+0x0/0x12c) from [<c005a0d4>] (notifier_call_chain+0x38/0x7c)
[<c005a09c>] (notifier_call_chain+0x0/0x7c) from [<c005a3a0>] (__blocking_notifier_call_chain+0x54/0x6c)
 r8:c3b51ea0 r7:00000009 r6:ffffffff r5:c0427a40 r4:c0427a74
[<c005a34c>] (__blocking_notifier_call_chain+0x0/0x6c) from [<c005a3d8>] (blocking_notifier_call_chain+0x20/0x28)
 r8:00000001 r7:c3a7e000 r6:00000000 r5:00000000 r4:c38984b8
[<c005a3b8>] (blocking_notifier_call_chain+0x0/0x28) from [<c014baa0>] (fb_notifier_call_chain+0x1c/0x24)
[<c014ba84>] (fb_notifier_call_chain+0x0/0x24) from [<c014c18c>] (fb_blank+0x64/0x70)
[<c014c128>] (fb_blank+0x0/0x70) from [<c014e450>] (store_blank+0x54/0x7c)
 r5:c38984b8 r4:c3b51ec4
[<c014e3fc>] (store_blank+0x0/0x7c) from [<c017981c>] (dev_attr_store+0x28/0x2c)
 r8:00000001 r7:c042bf80 r6:c39eba10 r5:c3967c30 r4:c38e0140
[<c01797f4>] (dev_attr_store+0x0/0x2c) from [<c00ddaac>] (flush_write_buffer+0x54/0x68)
[<c00dda58>] (flush_write_buffer+0x0/0x68) from [<c00dde08>] (sysfs_write_file+0x58/0x80)
 r8:c3b51f78 r7:c3bcb070 r6:c39eba10 r5:00000001 r4:00000001
[<c00dddb0>] (sysfs_write_file+0x0/0x80) from [<c009de04>] (vfs_write+0xb8/0x148)
[<c009dd4c>] (vfs_write+0x0/0x148) from [<c009e384>] (sys_write+0x44/0x70)
 r7:00000004 r6:c3bcb070 r5:00000000 r4:00000000
[<c009e340>] (sys_write+0x0/0x70) from [<c0025d00>] (ret_fast_syscall+0x0/0x2c)
 r6:4001b000 r5:00000001 r4:401dc658

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Reported-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Testted-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>