Commit 5a334c08 authored Dec 20, 2012 by Michael Holzheu Committed by Martin Schwidefsky Jan 08, 2013

s390/debug: Fix s390dbf lockdep problem in debug_(un)register_view()



The debug_register/unregister_view() functions call debugfs_remove()
while holding the debug_info spinlock. Because debugfs_remove() takes
a mutex and therefore can sleep this is not allowed. To fix the problem
we give up the debug_info lock before calling debugfs_remove().

The following shows the lockdep message:

[ INFO: possible circular locking dependency detected ]
-------------------------------------------------------
rmmod/4379 is trying to acquire lock:
(&sb->s_type->i_mutex_key#2){+.+.+.}, at: [<00000000003acae2>] debugfs_remove+0x5e/0xa

but task is already holding lock:
(&(&rc->lock)->rlock){-.-...}, at: [<000000000010a5ae>] debug_unregister_view+0x3a/0xd

which lock already depends on the new lock.

-> #0 (&sb->s_type->i_mutex_key#2){+.+.+.}:
[<00000000001b1644>] validate_chain+0x880/0x1154
[<00000000001b4d6c>] __lock_acquire+0x414/0xc44
[<00000000001b5c16>] lock_acquire+0xbe/0x178
[<0000000000614016>] mutex_lock_nested+0x66/0x36c
[<00000000003acae2>] debugfs_remove+0x5e/0xac
[<000000000010a620>] debug_unregister_view+0xac/0xd0
[<000003ff8002f140>] qeth_core_exit+0x48/0xf08 [qeth]
[<00000000001c35a4>] SyS_delete_module+0x1a4/0x260
[<0000000000618134>] sysc_noemu+0x22/0x28
[<000003fffd4704da>] 0x3fffd4704da

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent 2a893f91

arch/s390/kernel/debug.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -1127,13 +1127,14 @@ debug_register_view(debug_info_t * id, struct debug_view *view)
		if (i == DEBUG_MAX_VIEWS) {
		pr_err("Registering view %s/%s would exceed the maximum "
		"number of views %i\n", id->name, view->name, i);
		debugfs_remove(pde);
		rc = -1;
		} else {
		id->views[i] = view;
		id->debugfs_entries[i] = pde;
		}
		spin_unlock_irqrestore(&id->lock, flags);
		if (rc)
		debugfs_remove(pde);
		out:
		return rc;
		}
		@@ -1146,9 +1147,9 @@ EXPORT_SYMBOL(debug_register_view);
		int
		debug_unregister_view(debug_info_t * id, struct debug_view *view)
		{
		int rc = 0;
		int i;
		struct dentry *dentry = NULL;
		unsigned long flags;
		int i, rc = 0;

		if (!id)
		goto out;
		@@ -1160,10 +1161,12 @@ debug_unregister_view(debug_info_t * id, struct debug_view *view)
		if (i == DEBUG_MAX_VIEWS)
		rc = -1;
		else {
		debugfs_remove(id->debugfs_entries[i]);
		dentry = id->debugfs_entries[i];
		id->views[i] = NULL;
		id->debugfs_entries[i] = NULL;
		}
		spin_unlock_irqrestore(&id->lock, flags);
		debugfs_remove(dentry);
		out:
		return rc;
		}