[PATCH] lockdep: fix ide/proc interaction

rmmod/3080 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
(proc_subdir_lock){--..}, at: [<c04a33b0>] remove_proc_entry+0x40/0x191

and this task is already holding:
(ide_lock){++..}, at: [<c05651a2>] ide_unregister_subdriver+0x39/0xc8
which would create a new lock dependency:
(ide_lock){++..} -> (proc_subdir_lock){--..}

but this new dependency connects a hard-irq-safe lock:
(ide_lock){++..}
... which became hard-irq-safe at:
[<c043c458>] lock_acquire+0x4b/0x6b
[<c06129d7>] _spin_lock_irqsave+0x22/0x32
[<c0567870>] ide_intr+0x17/0x1a9
[<c044eb31>] handle_IRQ_event+0x20/0x4d
[<c044ebf2>] __do_IRQ+0x94/0xef
[<c0406771>] do_IRQ+0x9e/0xbd

to a hard-irq-unsafe lock:
(proc_subdir_lock){--..}
... which became hard-irq-unsafe at:
... [<c043c458>] lock_acquire+0x4b/0x6b
[<c06126ab>] _spin_lock+0x19/0x28
[<c04a32f2>] xlate_proc_name+0x1b/0x99
[<c04a3547>] proc_create+0x46/0xdf
[<c04a3642>] create_proc_entry+0x62/0xa5
[<c07c1972>] proc_misc_init+0x1c/0x1d2
[<c07c1844>] proc_root_init+0x4c/0xe9
[<c07ad703>] start_kernel+0x294/0x3b3

Move ide_remove_proc_entries() out from under ide_lock; there is nothing
that indicates that this is needed.

In specific, the call to ide_add_proc_entries() is unprotected, and there
is nothing else in the file using the respective ->proc fields. Also the
lock order around destroy_proc_ide_interface() suggests this.

Alan sayeth:

proc_ide_write_settings walks the setting list under ide_setting_sem, read
ditto. remove_proc_entry is doing proc side housekeeping.

Looks fine to me, although that old code is such a mess anything could be
going on.

Signed-off-by: Peter Zijlstra <[e-mail]>
Cc: Alan Cox <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/ide/ide.c

···
  *	@drive: drive
  *
  *	Automatically remove all the driver specific settings for this
- *	drive. This function may sleep and must not be called from IRQ
- *	context. The caller must hold ide_setting_sem.
+ *	drive. This function may not be called from IRQ context. The
+ *	caller must hold ide_setting_sem.
  */
  
 static void auto_remove_settings (ide_drive_t *drive)
···
 {
 	unsigned long flags;
 	
-	down(&ide_setting_sem);
-	spin_lock_irqsave(&ide_lock, flags);
 #ifdef CONFIG_PROC_FS
 	ide_remove_proc_entries(drive->proc, driver->proc);
 #endif
+	down(&ide_setting_sem);
+	spin_lock_irqsave(&ide_lock, flags);
+	/*
+	 * ide_setting_sem protects the settings list
+	 * ide_lock protects the use of settings
+	 *
+	 * so we need to hold both, ide_settings_sem because we want to
+	 * modify the settings list, and ide_lock because we cannot take
+	 * a setting out that is being used.
+	 *
+	 * OTOH both ide_{read,write}_setting are only ever used under
+	 * ide_setting_sem.
+	 */
 	auto_remove_settings(drive);
 	spin_unlock_irqrestore(&ide_lock, flags);
 	up(&ide_setting_sem);