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 >
