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

On 11/23/2017 12:37 AM, Naveen N. Rao wrote:

Mahesh J Salgaonkar wrote:

quoted

From: Mahesh Salgaonkar <redacted>

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.

Fix this by not calling trace_tlbie() from native_hpte_clear().

Signed-off-by: Mahesh Salgaonkar <redacted>
Reported-by: Aneesh Kumar K.V <redacted>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/mm/hash_native_64.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/hash_native_64.c

b/arch/powerpc/mm/hash_native_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 @@

 DEFINE_RAW_SPINLOCK(native_tlbie_lock);

-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

psize, 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
rcu checks for tracing __tlbie()?
    trace_tlbie_rcuidle(0, 0, va, 0, 0, 0, 0);

It helps if tracepoint is not enabled. But with tracepoint enabled kexec
still fails. I think we should not have tracepoint in kexec path at all.
If someone enables it, kexec will definitely fail regardless of
CONFIG_LOCKDEP.

Thanks,
-Mahesh.