From 5a334c082fc91f0c342ba9c111b77cafb5266654 Mon Sep 17 00:00:00 2001 From: Michael Holzheu Date: Thu, 20 Dec 2012 17:30:52 +0100 Subject: [PATCH] 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 Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/debug.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c index ba500d8dc392..4e8215e0d4b6 100644 --- a/arch/s390/kernel/debug.c +++ b/arch/s390/kernel/debug.c @@ -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; } -- 2.30.2