When booting on 32-bit machines (seen on OpenRISC) I saw this warning
with CONFIG_DEBUG_MUTEXES turned on.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at kernel/locking/mutex.c:1242 __mutex_unlock_slowpath+0x328/0x3ec
DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current)
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 5.8.0-rc1-simple-smp-00005-g2864e2171db4-dirty #179
Call trace:
[<(ptrval)>] dump_stack+0x34/0x48
[<(ptrval)>] __warn+0x104/0x158
[<(ptrval)>] ? __mutex_unlock_slowpath+0x328/0x3ec
[<(ptrval)>] warn_slowpath_fmt+0x7c/0x94
[<(ptrval)>] __mutex_unlock_slowpath+0x328/0x3ec
[<(ptrval)>] mutex_unlock+0x18/0x28
[<(ptrval)>] __cpuhp_setup_state_cpuslocked.part.0+0x29c/0x2f4
[<(ptrval)>] ? page_alloc_cpu_dead+0x0/0x30
[<(ptrval)>] ? start_kernel+0x0/0x684
[<(ptrval)>] __cpuhp_setup_state+0x4c/0x5c
[<(ptrval)>] page_alloc_init+0x34/0x68
[<(ptrval)>] ? start_kernel+0x1a0/0x684
[<(ptrval)>] ? early_init_dt_scan_nodes+0x60/0x70
irq event stamp: 0
I traced this to kernel/locking/mutex.c storing 3 bits of MUTEX_FLAGS in
the task_struct pointer (mutex.owner). There is a comment saying that
task_structs are always aligned to L1_CACHE_BYTES. This is not true for
the init_task.
On 64-bit machines this is not a problem because symbol addresses are
naturally aligned to 64-bits providing 3 bits for MUTEX_FLAGS. Howerver,
for 32-bit machines the symbol address only has 2 bits available.
Fix this by setting init_task alignment to at least L1_CACHE_BYTES.
Signed-off-by: Stafford Horne <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
---
Changes since v1:
- Make alignment unconditional suggested by Peter
init/init_task.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/init/init_task.c b/init/init_task.c
index 15089d15010a..ab6173f8e6a8 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -65,6 +65,7 @@ struct task_struct init_task
#ifdef CONFIG_ARCH_TASK_STRUCT_ON_STACK
__init_task_data
#endif
+ __aligned(L1_CACHE_BYTES)
= {
#ifdef CONFIG_THREAD_INFO_IN_TASK
.thread_info = INIT_THREAD_INFO(init_task),
--
2.26.2
Hello,
Is there anyone willing to pick this up?
I guess I could send it in the OpenRISC queue, but it doesn't really seem like
the right thing.
-Stafford
On Sat, Jun 27, 2020 at 06:07:53AM +0900, Stafford Horne wrote:
> When booting on 32-bit machines (seen on OpenRISC) I saw this warning
> with CONFIG_DEBUG_MUTEXES turned on.
>
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 0 at kernel/locking/mutex.c:1242 __mutex_unlock_slowpath+0x328/0x3ec
> DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current)
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.8.0-rc1-simple-smp-00005-g2864e2171db4-dirty #179
> Call trace:
> [<(ptrval)>] dump_stack+0x34/0x48
> [<(ptrval)>] __warn+0x104/0x158
> [<(ptrval)>] ? __mutex_unlock_slowpath+0x328/0x3ec
> [<(ptrval)>] warn_slowpath_fmt+0x7c/0x94
> [<(ptrval)>] __mutex_unlock_slowpath+0x328/0x3ec
> [<(ptrval)>] mutex_unlock+0x18/0x28
> [<(ptrval)>] __cpuhp_setup_state_cpuslocked.part.0+0x29c/0x2f4
> [<(ptrval)>] ? page_alloc_cpu_dead+0x0/0x30
> [<(ptrval)>] ? start_kernel+0x0/0x684
> [<(ptrval)>] __cpuhp_setup_state+0x4c/0x5c
> [<(ptrval)>] page_alloc_init+0x34/0x68
> [<(ptrval)>] ? start_kernel+0x1a0/0x684
> [<(ptrval)>] ? early_init_dt_scan_nodes+0x60/0x70
> irq event stamp: 0
>
> I traced this to kernel/locking/mutex.c storing 3 bits of MUTEX_FLAGS in
> the task_struct pointer (mutex.owner). There is a comment saying that
> task_structs are always aligned to L1_CACHE_BYTES. This is not true for
> the init_task.
>
> On 64-bit machines this is not a problem because symbol addresses are
> naturally aligned to 64-bits providing 3 bits for MUTEX_FLAGS. Howerver,
> for 32-bit machines the symbol address only has 2 bits available.
>
> Fix this by setting init_task alignment to at least L1_CACHE_BYTES.
>
> Signed-off-by: Stafford Horne <[email protected]>
> Acked-by: Peter Zijlstra (Intel) <[email protected]>
> ---
> Changes since v1:
> - Make alignment unconditional suggested by Peter
>
> init/init_task.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/init/init_task.c b/init/init_task.c
> index 15089d15010a..ab6173f8e6a8 100644
> --- a/init/init_task.c
> +++ b/init/init_task.c
> @@ -65,6 +65,7 @@ struct task_struct init_task
> #ifdef CONFIG_ARCH_TASK_STRUCT_ON_STACK
> __init_task_data
> #endif
> + __aligned(L1_CACHE_BYTES)
> = {
> #ifdef CONFIG_THREAD_INFO_IN_TASK
> .thread_info = INIT_THREAD_INFO(init_task),
> --
> 2.26.2
>