linux-kernel - Re: [PATCH smp 0/2] Provide CSD lock timeout diagnostics

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Date:   Mon, 27 Jul 2020 16:53:43 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...nel.org, tglx@...utronix.de,
        bigeasy@...utronix.de, frederic@...nel.org
Subject: Re: [PATCH smp 0/2] Provide CSD lock timeout diagnostics

Hello!

This is version 2 of a sneak preview of a series providing diagnostics
to help track down problems that would result in excessive csd_unlock()
latencies:

1.	Add source and destination CPUs to __call_single_data.
	I freely admit that I found the union declaration a
	bit confusing!

2.	Provide CSD lock timeout diagnostics.

3.	Add "static" to a local variable.

Changes since v1:

o	Fix stack-out-of-bounds read in csd_lock_record located by syzbot.

o	Fix KASAN-detected use-after-free issue reported by Qian Cai.

o	Fix botched nr_cpu_ids comparison reported by Dan Carpenter.

o	Fix numerous issues reported by Peter Zijlstra, including
	annoying CPP macros, #ifdef consolidation, another use-after-free
	issue, memory-ordering/comment issues, {} code-style issues.

	This now has no effect unless CONFIG_CSD_LOCK_WAIT_DEBUG=y.
	It also uses NSEC_PER_MSEC instead of cubing 1000.
	Times are now printed in nanoseconds instead of decimal seconds.
	Switched to C-language Classic Comment style.
	Moved to x-mas tree variable-declaration order from alphabetic.
	Avoided two prints via "CPU-1".

o	This version still "handles" 32-bit VDSO build errors by
	prohibiting CONFIG_CSD_LOCK_WAIT_DEBUG=y in 32-bit builds.

						Thanx, Paul

------------------------------------------------------------------------

 include/linux/smp.h       |    3 +
 include/linux/smp_types.h |    3 +
 kernel/smp.c              |  136 +++++++++++++++++++++++++++++++++++++++++++++-
 lib/Kconfig.debug         |   11 +++
 4 files changed, 152 insertions(+), 1 deletion(-)