Re: [PATCH] powernv: Avoid calling trace tlbie in kexec path.

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
>=20
> Rebooting into a new kernel with kexec fails in trace_tlbie() which is
> called from native_hpte_clear(). This happens if the running kernel has
> CONFIG_LOCKDEP enabled. With lockdep enabled, the tracepoints always
> execute few RCU checks regardless of whether tracing is on or off.
> We are already in the last phase of kexec sequence in real mode with
> HILE_BE set. At this point the RCU check ends up in RCU_LOCKDEP_WARN and
> causes kexec to fail.
>=20
> Fix this by not calling trace_tlbie() from native_hpte_clear().
>=20
> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>  arch/powerpc/mm/hash_native_64.c |   15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>=20
> diff --git a/arch/powerpc/mm/hash_native_64.c b/arch/powerpc/mm/hash_nati=
ve_64.c
> index 3848af1..640cf56 100644
> --- a/arch/powerpc/mm/hash_native_64.c
> +++ b/arch/powerpc/mm/hash_native_64.c
> @@ -47,7 +47,8 @@
>=20
>  DEFINE_RAW_SPINLOCK(native_tlbie_lock);
>=20
> -static inline void __tlbie(unsigned long vpn, int psize, int apsize, int=
 ssize)
> +static inline unsigned long  ___tlbie(unsigned long vpn, int psize,
> +						int apsize, int ssize)
>  {
>  	unsigned long va;
>  	unsigned int penc;
> @@ -100,7 +101,15 @@ static inline void __tlbie(unsigned long vpn, int ps=
ize, int apsize, int ssize)
>  			     : "memory");
>  		break;
>  	}
> -	trace_tlbie(0, 0, va, 0, 0, 0, 0);

Does it help if you use the _rcuidle variant instead, to turn off all=20
rcu checks for tracing __tlbie()?
	trace_tlbie_rcuidle(0, 0, va, 0, 0, 0, 0);


- Naveen

=