This is my proposal to print the NMI stack traces from an RCU stall safely.
Here's the gist of it.
Patch 1: move the trace_seq out of the tracing code. It's useful for other
purposes too. Like writing from an NMI context.
Patch 2: Add a per_cpu "printk_func" that printk calls. By default it calls
vprintk_def() which does what it has always done. This allows us to
override what printk() calls normally on a per cpu basis.
Patch 3: Have the NMI handler that dumps the stack trace just change the
printk_func to call a NMI safe printk function that writes to a per cpu
trace_seq. When all NMI handlers chimed in, the original caller prints
out the trace_seqs for each CPU from a printk safe context.
This is much less intrusive than the other versions out there.
Note, The biggest change was the moving of trace_seq code out of trace_output.c
and into the new trace_seq.c library.
Thoughts?
Steven Rostedt (Red Hat) (3):
trace_seq: Move the trace_seq code to lib/
printk: Add per_cpu printk func to allow printk to be diverted
x86/nmi: Perform a safe NMI stack trace on all CPUs
----
arch/x86/kernel/apic/hw_nmi.c | 66 ++++++++-
include/linux/percpu.h | 3 +
include/linux/printk.h | 2 +
include/linux/trace_seq.h | 68 ++--------
kernel/printk/printk.c | 38 ++++--
kernel/trace/trace.c | 24 ----
kernel/trace/trace_output.c | 268 -------------------------------------
kernel/trace/trace_output.h | 16 ---
lib/Makefile | 2 +-
lib/trace_seq.c | 303 ++++++++++++++++++++++++++++++++++++++++++
10 files changed, 412 insertions(+), 378 deletions(-)
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