Re: [PATCH 2/2] powerpc/book3s: mce: Use add_taint_no_warn() in machine_check_early().
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2017-04-11 10:35:20
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Mahesh J Salgaonkar [off-list ref] writes:
From: Mahesh Salgaonkar <redacted> machine_check_early() gets called in real mode. The very first time when add_taint() is called, it prints a warning which ends up calling opal call (that uses OPAL_CALL wrapper) for writing it to console. If we get a very first machine check while we are in opal we are doomed. OPAL_CALL overwrites the PACASAVEDMSR in r13 and in this case when we are done with MCE handling the original opal call will use this new MSR on it's way back to opal_return. This usually leads unexpected behaviour or kernel to panic. Instead use the add_taint_no_warn() that does not call printk. This is broken with current FW level. We got lucky so far for not getting very first MCE hit while in OPAL. But easily reproducible on Mambo. This should go to stable as well alongwith patch 1/2.
This is not a good way to fix a bug that needs to go back to stable. Changing generic code means I need to sync up with the right maintainer, get acks, etc. And then convince people that it should go to stable also. So you can please fix this a different way for stable? Can we just do the tainting later, once we're in virtual mode? cheers
quoted hunk ↗ jump to hunk
Fixes: 27ea2c420cad powerpc: Set the correct kernel taint on machine check errors. Signed-off-by: Mahesh Salgaonkar <redacted> --- arch/powerpc/kernel/traps.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index 62b587f..4a048dc 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c@@ -306,7 +306,7 @@ long machine_check_early(struct pt_regs *regs) __this_cpu_inc(irq_stat.mce_exceptions); - add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE); + add_taint_no_warn(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE); /* * See if platform is capable of handling machine check. (e.g. PowerNV