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SubjectRe: [PATCH -next] lockdep: skip debugobjects for lock_classes[] init
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On 3/2/19 8:02 PM, Qian Cai wrote:
> The linux-next commit a0b0fd53e1e6 ("locking/lockdep: Free lock classes
> that are no longer in use") let init_data_structures_once() call
> init_rcu_head(). As the result, smp_setup_processor_id() calls
> debug_object_init() before debug_objects_early_init() triggering errors
> below on arm64 and ppc64le. Since debug_objects_early_init() depends on
> smp_setup_processor_id(), so it is not straightforward to move the
> former earlier in start_kernel(). Hence, just skip all debugobjects
> creations in init_data_structures_once() as a good trade-off by losing
> track of some RCU list heads debugging.
>
> BUG: spinlock bad magic on CPU#0, swapper/0
> lock: obj_hash+0xc3048/0x100000, .magic: 00000000, .owner: <none>/-1,
> .owner_cpu: 0
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc8-next-20190301+ #1
> Call trace:
> dump_backtrace+0x0/0x450
> show_stack+0x20/0x2c
> dump_stack+0xe0/0x16c
> spin_bug+0x200/0x224
> do_raw_spin_lock+0x1bc/0x23c
> _raw_spin_lock_irqsave+0xac/0xd0
> __debug_object_init+0xf0/0x19dc
> debug_object_init+0x54/0x6c
> init_rcu_head+0x24/0x30
> init_data_structures_once+0xb0/0x41c
> register_lock_class+0x70c/0x1454
> __lock_acquire+0xc4/0x235c
> lock_acquire+0x508/0x668
> _raw_spin_lock+0x88/0xac
> vprintk_emit+0x33c/0x53c
> vprintk_default+0x54/0x7c
> vprintk_func+0x320/0x40c
> printk+0x64/0x8c
> smp_setup_processor_id+0x6c/0x84
> start_kernel+0x38/0x8f8
> ODEBUG: Out of memory. ODEBUG disabled
>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> kernel/locking/lockdep.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 21cb81fe6359..1309a6fe88ee 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -988,7 +988,6 @@ static void init_data_structures_once(void)
>
> initialization_happened = true;
>
> - init_rcu_head(&delayed_free.rcu_head);
> INIT_LIST_HEAD(&delayed_free.pf[0].zapped);
> INIT_LIST_HEAD(&delayed_free.pf[1].zapped);

Hi Qian,

Thanks for having reported this issue. Had you considered to follow an
approach similar to the patch below?

Thanks,

Bart.


[PATCH] locking/lockdep: Only call init_rcu_head() after RCU has been
initialized

init_data_structures_once() is called for the first time before RCU has
been initialized. Make sure that init_rcu_head() is called before the
RCU head is used and after RCU has been initialized.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
kernel/locking/lockdep.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 21cb81fe6359..c8c83e1e2664 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -980,15 +980,22 @@ static inline void check_data_structures(void) { }
*/
static void init_data_structures_once(void)
{
- static bool initialization_happened;
+ static bool ds_initialized, rcu_head_initialized;
int i;

- if (likely(initialization_happened))
+ if (likely(rcu_head_initialized))
return;

- initialization_happened = true;
+ if (system_state >= SYSTEM_SCHEDULING) {
+ init_rcu_head(&delayed_free.rcu_head);
+ rcu_head_initialized = true;
+ }
+
+ if (ds_initialized)
+ return;
+
+ ds_initialized = true;

- init_rcu_head(&delayed_free.rcu_head);
INIT_LIST_HEAD(&delayed_free.pf[0].zapped);
INIT_LIST_HEAD(&delayed_free.pf[1].zapped);

--
2.20.1
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