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SubjectRe: [BUG] Lockdep warning with XFS on 2.6.22-rc6

* Satyam Sharma <satyam.sharma@gmail.com> wrote:

> [ Ok, so we know that XFS wants to lock inodes in ascending inode
> number order and not strictly the parent-first-child-second order that
> rest of the fs/ code does, so that makes it difficult to teach lockdep
> about this kind of lock ordering ... ]

hm, there's a recent API addition to lockdep that should help with this:
have you looked into the patch below, could it be used to solve the XFS
problem? Basically when you are one step deeper into a recursive locking
scenario you can use lock_set_subclass() on the held lock to reset it
one level higher.

this preserves lockdep checking but allows arbitrary deep locking.

Ingo

---------------------->
Subject: [patch] lockdep: lock_set_subclass - reset a held lock's subclass
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
this can be used to reset a held lock's subclass, for arbitrary-depth
iterated data structures such as trees or lists which have per-node
locks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/lockdep.h | 4 ++
kernel/lockdep.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 73 insertions(+)
Index: linux/include/linux/lockdep.h
===================================================================
--- linux.orig/include/linux/lockdep.h
+++ linux/include/linux/lockdep.h
@@ -243,6 +243,9 @@ extern void lock_acquire(struct lockdep_
extern void lock_release(struct lockdep_map *lock, int nested,
unsigned long ip);

+extern void lock_set_subclass(struct lockdep_map *lock, unsigned int subclass,
+ unsigned long ip);
+
# define INIT_LOCKDEP .lockdep_recursion = 0,

#define lockdep_depth(tsk) (debug_locks ? (tsk)->lockdep_depth : 0)
@@ -259,6 +262,7 @@ static inline void lockdep_on(void)

# define lock_acquire(l, s, t, r, c, i) do { } while (0)
# define lock_release(l, n, i) do { } while (0)
+# define lock_set_subclass(l, s, i) do { } while (0)
# define lockdep_init() do { } while (0)
# define lockdep_info() do { } while (0)
# define lockdep_init_map(lock, name, key, sub) do { (void)(key); } while (0)
Index: linux/kernel/lockdep.c
===================================================================
--- linux.orig/kernel/lockdep.c
+++ linux/kernel/lockdep.c
@@ -2278,6 +2278,55 @@ static int check_unlock(struct task_stru
return 1;
}

+static int
+__lock_set_subclass(struct lockdep_map *lock,
+ unsigned int subclass, unsigned long ip)
+{
+ struct task_struct *curr = current;
+ struct held_lock *hlock, *prev_hlock;
+ struct lock_class *class;
+ unsigned int depth;
+ int i;
+
+ depth = curr->lockdep_depth;
+ if (DEBUG_LOCKS_WARN_ON(!depth))
+ return 0;
+
+ prev_hlock = NULL;
+ for (i = depth-1; i >= 0; i--) {
+ hlock = curr->held_locks + i;
+ /*
+ * We must not cross into another context:
+ */
+ if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
+ break;
+ if (hlock->instance == lock)
+ goto found_it;
+ prev_hlock = hlock;
+ }
+ return print_unlock_inbalance_bug(curr, lock, ip);
+
+found_it:
+ class = register_lock_class(lock, subclass, 0);
+ hlock->class = class;
+
+ curr->lockdep_depth = i;
+ curr->curr_chain_key = hlock->prev_chain_key;
+
+ for (; i < depth; i++) {
+ hlock = curr->held_locks + i;
+ if (!__lock_acquire(hlock->instance,
+ hlock->class->subclass, hlock->trylock,
+ hlock->read, hlock->check, hlock->hardirqs_off,
+ hlock->acquire_ip))
+ return 0;
+ }
+
+ if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
+ return 0;
+ return 1;
+}
+
/*
* Remove the lock to the list of currently held locks in a
* potentially non-nested (out of order) manner. This is a
@@ -2473,6 +2522,26 @@ void lock_release(struct lockdep_map *lo

EXPORT_SYMBOL_GPL(lock_release);

+void
+lock_set_subclass(struct lockdep_map *lock,
+ unsigned int subclass, unsigned long ip)
+{
+ unsigned long flags;
+
+ if (unlikely(current->lockdep_recursion))
+ return;
+
+ raw_local_irq_save(flags);
+ current->lockdep_recursion = 1;
+ check_flags(flags);
+ if (__lock_set_subclass(lock, subclass, ip))
+ check_chain_key(current);
+ current->lockdep_recursion = 0;
+ raw_local_irq_restore(flags);
+}
+
+EXPORT_SYMBOL_GPL(lock_set_subclass);
+
/*
* Used by the testsuite, sanitize the validator state
* after a simulated failure:
-
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