Revert "lockdep: check that no locks held at freeze time"

This reverts commit 6aa97070.

Commit 6aa97070 ("lockdep: check that no locks held at freeze time")
causes problems with NFS root filesystems.  The failures were noticed on
OMAP2 and 3 boards during kernel init:

  [ BUG: swapper/0/1 still has locks held! ]
  3.9.0-rc3-00344-ga937536b #1 Not tainted
  -------------------------------------
  1 lock held by swapper/0/1:
   #0:  (&type->s_umount_key#13/1){+.+.+.}, at: [<c011e84c>] sget+0x248/0x574

  stack backtrace:
    rpc_wait_bit_killable
    __wait_on_bit
    out_of_line_wait_on_bit
    __rpc_execute
    rpc_run_task
    rpc_call_sync
    nfs_proc_get_root
    nfs_get_root
    nfs_fs_mount_common
    nfs_try_mount
    nfs_fs_mount
    mount_fs
    vfs_kern_mount
    do_mount
    sys_mount
    do_mount_root
    mount_root
    prepare_namespace
    kernel_init_freeable
    kernel_init

Although the rootfs mounts, the system is unstable.  Here's a transcript
from a PM test:

  http://www.pwsan.com/omap/testlogs/test_v3.9-rc3/20130317194234/pm/37xxevm/37xxevm_log.txt

Here's what the test log should look like:

  http://www.pwsan.com/omap/testlogs/test_v3.8/20130218214403/pm/37xxevm/37xxevm_log.txt

Mailing list discussion is here:

  http://lkml.org/lkml/2013/3/4/221

Deal with this for v3.9 by reverting the problem commit, until folks can
figure out the right long-term course of action.
Signed-off-by: NPaul Walmsley <paul@pwsan.com>
Cc: Mandeep Singh Baines <msb@chromium.org>
Cc: Jeff Layton <jlayton@redhat.com>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: <maciej.rutecki@gmail.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ben Chan <benchan@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/debug_locks.h

@@ -51,7 +51,7 @@ struct task_struct;
 extern void debug_show_all_locks(void);
 extern void debug_show_held_locks(struct task_struct *task);
 extern void debug_check_no_locks_freed(const void *from, unsigned long len);
-extern void debug_check_no_locks_held(void);
+extern void debug_check_no_locks_held(struct task_struct *task);
 #else
 static inline void debug_show_all_locks(void)
 {
@@ -67,7 +67,7 @@ debug_check_no_locks_freed(const void *from, unsigned long len)
 }
 
 static inline void
-debug_check_no_locks_held(void)
+debug_check_no_locks_held(struct task_struct *task)
 {
 }
 #endif

include/linux/freezer.h

@@ -3,7 +3,6 @@
 #ifndef FREEZER_H_INCLUDED
 #define FREEZER_H_INCLUDED
 
-#include <linux/debug_locks.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/atomic.h>
@@ -49,8 +48,6 @@ extern void thaw_kernel_threads(void);
 
 static inline bool try_to_freeze(void)
 {
-	if (!(current->flags & PF_NOFREEZE))
-		debug_check_no_locks_held();
 	might_sleep();
 	if (likely(!freezing(current)))
 		return false;

kernel/exit.c

@@ -835,7 +835,7 @@ void do_exit(long code)
 	/*
 	 * Make sure we are holding no locks:
 	 */
-	debug_check_no_locks_held();
+	debug_check_no_locks_held(tsk);
 	/*
 	 * We can do this unlocked here. The futex code uses this flag
 	 * just to verify whether the pi state cleanup has been done

kernel/lockdep.c

@@ -4088,7 +4088,7 @@ void debug_check_no_locks_freed(const void *mem_from, unsigned long mem_len)
 }
 EXPORT_SYMBOL_GPL(debug_check_no_locks_freed);
 
-static void print_held_locks_bug(void)
+static void print_held_locks_bug(struct task_struct *curr)
 {
 	if (!debug_locks_off())
 		return;
@@ -4097,21 +4097,22 @@ static void print_held_locks_bug(void)
 
 	printk("\n");
 	printk("=====================================\n");
-	printk("[ BUG: %s/%d still has locks held! ]\n",
-	       current->comm, task_pid_nr(current));
+	printk("[ BUG: lock held at task exit time! ]\n");
 	print_kernel_ident();
 	printk("-------------------------------------\n");
-	lockdep_print_held_locks(current);
+	printk("%s/%d is exiting with locks still held!\n",
+		curr->comm, task_pid_nr(curr));
+	lockdep_print_held_locks(curr);
+
 	printk("\nstack backtrace:\n");
 	dump_stack();
 }
 
-void debug_check_no_locks_held(void)
+void debug_check_no_locks_held(struct task_struct *task)
 {
-	if (unlikely(current->lockdep_depth > 0))
-		print_held_locks_bug();
+	if (unlikely(task->lockdep_depth > 0))
+		print_held_locks_bug(task);
 }
-EXPORT_SYMBOL_GPL(debug_check_no_locks_held);
 
 void debug_show_all_locks(void)
 {