On Fri, Jun 26, 2020 at 05:44:09AM +0900, Stafford Horne wrote: > When booting on 32-bit machines (seen on OpenRISC) I saw this warning > with CONFIG_DEBUG_MUTEXES turned on.
> 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. Whoopsie, sorry about that. > Cc: Peter Zijlstra <pet...@infradead.org> > Signed-off-by: Stafford Horne <sho...@gmail.com> > --- > init/init_task.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/init/init_task.c b/init/init_task.c > index 15089d15010a..d2d2af018d0d 100644 > --- a/init/init_task.c > +++ b/init/init_task.c > @@ -64,6 +64,8 @@ unsigned long init_shadow_call_stack[SCS_SIZE / > sizeof(long)] > struct task_struct init_task > #ifdef CONFIG_ARCH_TASK_STRUCT_ON_STACK > __init_task_data > +#else > + __aligned(L1_CACHE_BYTES) > #endif Why make this conditional? task_struct_cachep (in kernel/fork.c) has max_t(int, L1_CACHE_BYTES, ARCH_MIN_TASKALIGN) alignment, so this really should be aligned on L1_CACHE_BYTES at least.
