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

Mahesh Jagannath Salgaonkar wrote:

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

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Mahesh J Salgaonkar wrote:

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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 an=

d

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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>
---
=C2=A0arch/powerpc/mm/hash_native_64.c |=C2=A0=C2=A0 15 ++++++++++++---
=C2=A01 file changed, 12 insertions(+), 3 deletions(-)

[snip]

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@@ -100,7 +101,15 @@ static inline void __tlbie(unsigned long vpn,=20

int
psize, int apsize, int ssize)
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=

=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : "memory");

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=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 break;
=C2=A0=C2=A0=C2=A0=C2=A0 }
-=C2=A0=C2=A0=C2=A0 trace_tlbie(0, 0, va, 0, 0, 0, 0);

=20
Does it help if you use the _rcuidle variant instead, to turn off all
rcu checks for tracing __tlbie()?
=C2=A0=C2=A0=C2=A0=C2=A0trace_tlbie_rcuidle(0, 0, va, 0, 0, 0, 0);

=20
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.

Ok, thanks for confirming that other tracepoints don't interfere with=20
kexec. As Balbir points out, moving to TRACE_EVENT_CONDITION() with a=20
global in_kexec variable may be the other option, but is probably=20
overkill for a single tracepoint.

Acked-by: Naveen N. Rao <redacted>


Thanks,
Naveen

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